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EQ2EMu
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Датотеке Дискусије 63 Захтеви за спајање 0 Вики
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EQ2EMu
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EQ2
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boost_1_72_0
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libs
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reference.html

reference.html 403 KB
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  7. <title>The Boost Parameter Library Reference Documentation</title>
    8. 

  8. <meta name="authors" content="David Abrahams  Daniel Wallin" />
    9. 

  9. <meta name="organization" content="BoostPro Computing" />
    10. 

  10. <meta name="date" content="2005-07-17" />
    11. 

  11. <meta name="copyright" content="Copyright David Abrahams, Daniel Wallin 2005-2009.  Distributed under the Boost Software License, Version 1.0.  (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)" />
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  15. <div class="document" id="the-boost-parameter-library-reference-documentation">
    16. 

  16. <h1 class="title">The Boost Parameter Library Reference Documentation</h1>
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  17. <table class="docinfo" frame="void" rules="none">
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  18. <col class="docinfo-name" />
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  19. <col class="docinfo-content" />
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  20. <tbody valign="top">
    21. 

  21. <tr><th class="docinfo-name">Authors:</th>
    22. 

  22. <td>David Abrahams
    23. 

  23. <br />Daniel Wallin</td></tr>
    24. 

  24. <tr><th class="docinfo-name">Contact:</th>
    25. 

  25. <td><a class="first reference external" href="mailto:dave&#64;boost-consulting.com">dave&#64;boost-consulting.com</a>, <a class="last reference external" href="mailto:daniel&#64;boostpro.com">daniel&#64;boostpro.com</a></td></tr>
    26. 

  26. <tr><th class="docinfo-name">Organization:</th>
    27. 

  27. <td><a class="first last reference external" href="http://www.boostpro.com">BoostPro Computing</a></td></tr>
    28. 

  28. <tr><th class="docinfo-name">Date:</th>
    29. 

  29. <td>2005-07-17</td></tr>
    30. 

  30. <tr><th class="docinfo-name">Copyright:</th>
    31. 

  31. <td>Copyright David Abrahams, Daniel Wallin
    32. 

  32. 2005-2009.  Distributed under the Boost Software License,
    33. 

  33. Version 1.0.  (See accompanying file LICENSE_1_0.txt
    34. 

  34. or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</td></tr>
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  35. </tbody>
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  37. <p><a class="reference external" href="../../../../index.htm"><img alt="Boost" src="../../../../boost.png" /></a></p>
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  38. <hr class="docutils" />
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  39. <div class="contents topic" id="contents">
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  40. <p class="topic-title first">Contents</p>
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  41. <ul class="auto-toc simple">
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  42. <li><a class="reference internal" href="#preliminaries" id="id31">1&nbsp;&nbsp;&nbsp;Preliminaries</a><ul class="auto-toc">
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  43. <li><a class="reference internal" href="#namespaces" id="id32">1.1&nbsp;&nbsp;&nbsp;Namespaces</a></li>
    44. 

  44. <li><a class="reference internal" href="#exceptions" id="id33">1.2&nbsp;&nbsp;&nbsp;Exceptions</a></li>
    45. 

  45. <li><a class="reference internal" href="#thread-safety" id="id34">1.3&nbsp;&nbsp;&nbsp;Thread Safety</a></li>
    46. 

  46. <li><a class="reference internal" href="#typography" id="id35">1.4&nbsp;&nbsp;&nbsp;Typography</a></li>
    47. 

  47. </ul>
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  48. </li>
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  49. <li><a class="reference internal" href="#terminology" id="id36">2&nbsp;&nbsp;&nbsp;Terminology</a></li>
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  50. <li><a class="reference internal" href="#concepts" id="id37">3&nbsp;&nbsp;&nbsp;Concepts</a><ul class="auto-toc">
    51. 

  51. <li><a class="reference internal" href="#argumentpack" id="id38">3.1&nbsp;&nbsp;&nbsp;<span class="concept">ArgumentPack</span></a></li>
    52. 

  52. <li><a class="reference internal" href="#id3" id="id39">3.2&nbsp;&nbsp;&nbsp;<span class="concept">ParameterSpec</span></a></li>
    53. 

  53. </ul>
    54. 

  54. </li>
    55. 

  55. <li><a class="reference internal" href="#class-templates" id="id40">4&nbsp;&nbsp;&nbsp;Class Templates</a><ul class="auto-toc">
    56. 

  56. <li><a class="reference internal" href="#id5" id="id41">4.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">keyword</tt></a></li>
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  57. <li><a class="reference internal" href="#id7" id="id42">4.2&nbsp;&nbsp;&nbsp;<tt class="docutils literal">template_keyword</tt></a></li>
    58. 

  58. <li><a class="reference internal" href="#id8" id="id43">4.3&nbsp;&nbsp;&nbsp;<tt class="docutils literal">parameters</tt></a></li>
    59. 

  59. <li><a class="reference internal" href="#optional-required" id="id44">4.4&nbsp;&nbsp;&nbsp;<tt class="docutils literal">optional</tt>, <tt class="docutils literal">required</tt></a></li>
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  60. <li><a class="reference internal" href="#id9" id="id45">4.5&nbsp;&nbsp;&nbsp;<tt class="docutils literal">deduced</tt></a></li>
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  61. </ul>
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  62. </li>
    63. 

  63. <li><a class="reference internal" href="#metafunctions" id="id46">5&nbsp;&nbsp;&nbsp;Metafunctions</a><ul class="auto-toc">
    64. 

  64. <li><a class="reference internal" href="#id10" id="id47">5.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">binding</tt></a></li>
    65. 

  65. <li><a class="reference internal" href="#id11" id="id48">5.2&nbsp;&nbsp;&nbsp;<tt class="docutils literal">lazy_binding</tt></a></li>
    66. 

  66. <li><a class="reference internal" href="#id13" id="id49">5.3&nbsp;&nbsp;&nbsp;<tt class="docutils literal">value_type</tt></a></li>
    67. 

  67. <li><a class="reference internal" href="#id14" id="id50">5.4&nbsp;&nbsp;&nbsp;<tt class="docutils literal">lazy_value_type</tt></a></li>
    68. 

  68. <li><a class="reference internal" href="#id16" id="id51">5.5&nbsp;&nbsp;&nbsp;<tt class="docutils literal">are_tagged_arguments</tt></a></li>
    69. 

  69. <li><a class="reference internal" href="#id17" id="id52">5.6&nbsp;&nbsp;&nbsp;<tt class="docutils literal">is_argument_pack</tt></a></li>
    70. 

  70. <li><a class="reference internal" href="#id18" id="id53">5.7&nbsp;&nbsp;&nbsp;<tt class="docutils literal"><span class="pre">result_of::compose</span></tt></a></li>
    71. 

  71. </ul>
    72. 

  72. </li>
    73. 

  73. <li><a class="reference internal" href="#function-templates" id="id54">6&nbsp;&nbsp;&nbsp;Function Templates</a><ul class="auto-toc">
    74. 

  74. <li><a class="reference internal" href="#id19" id="id55">6.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">compose</tt></a></li>
    75. 

  75. </ul>
    76. 

  76. </li>
    77. 

  77. <li><a class="reference internal" href="#code-generation-macros" id="id56">7&nbsp;&nbsp;&nbsp;Code Generation Macros</a><ul class="auto-toc">
    78. 

  78. <li><a class="reference internal" href="#boost-parameter-function-result-name-tag-namespace-arguments" id="id57">7.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_FUNCTION(result, name, tag_namespace, arguments)</tt></a></li>
    79. 

  79. <li><a class="reference internal" href="#boost-parameter-member-function-result-name-tag-namespace-arguments" id="id58">7.2&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_MEMBER_FUNCTION(result, name, tag_namespace, arguments)</tt></a></li>
    80. 

  80. <li><a class="reference internal" href="#boost-parameter-const-member-function-result-name-tag-ns-arguments" id="id59">7.3&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_CONST_MEMBER_FUNCTION(result, name, tag_ns, arguments)</tt></a></li>
    81. 

  81. <li><a class="reference internal" href="#boost-parameter-function-call-operator-result-tag-namespace-arguments" id="id60">7.4&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_FUNCTION_CALL_OPERATOR(result, tag_namespace, arguments)</tt></a></li>
    82. 

  82. <li><a class="reference internal" href="#boost-parameter-const-function-call-operator-result-tag-ns-arguments" id="id61">7.5&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)</tt></a></li>
    83. 

  83. <li><a class="reference internal" href="#boost-parameter-constructor-cls-impl-tag-namespace-arguments" id="id62">7.6&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_CONSTRUCTOR(cls, impl, tag_namespace, arguments)</tt></a></li>
    84. 

  84. <li><a class="reference internal" href="#boost-parameter-basic-function-result-name-tag-namespace-arguments" id="id63">7.7&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_FUNCTION(result, name, tag_namespace, arguments)</tt></a></li>
    85. 

  85. <li><a class="reference internal" href="#boost-parameter-basic-member-function-result-name-tag-ns-arguments" id="id64">7.8&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_MEMBER_FUNCTION(result, name, tag_ns, arguments)</tt></a></li>
    86. 

  86. <li><a class="reference internal" href="#boost-parameter-basic-const-member-function-result-name-tag-ns-args" id="id65">7.9&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION(result, name, tag_ns, args)</tt></a></li>
    87. 

  87. <li><a class="reference internal" href="#boost-parameter-basic-function-call-operator-result-tag-ns-arguments" id="id66">7.10&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)</tt></a></li>
    88. 

  88. <li><a class="reference internal" href="#boost-parameter-basic-const-function-call-operator-result-tag-ns-args" id="id67">7.11&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, args)</tt></a></li>
    89. 

  89. <li><a class="reference internal" href="#boost-parameter-no-spec-function-result-name" id="id68">7.12&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_FUNCTION(result, name)</tt></a></li>
    90. 

  90. <li><a class="reference internal" href="#boost-parameter-no-spec-member-function-result-name" id="id69">7.13&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION(result, name)</tt></a></li>
    91. 

  91. <li><a class="reference internal" href="#boost-parameter-no-spec-const-member-function-result-name" id="id70">7.14&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION(result, name)</tt></a></li>
    92. 

  92. <li><a class="reference internal" href="#boost-parameter-no-spec-function-call-operator-result" id="id71">7.15&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR(result)</tt></a></li>
    93. 

  93. <li><a class="reference internal" href="#boost-parameter-no-spec-const-function-call-operator-result" id="id72">7.16&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR(result)</tt></a></li>
    94. 

  94. <li><a class="reference internal" href="#boost-parameter-no-spec-constructor-cls-impl" id="id73">7.17&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR(cls, impl)</tt></a></li>
    95. 

  95. <li><a class="reference internal" href="#boost-parameter-no-spec-no-base-constructor-cls-impl" id="id74">7.18&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR(cls, impl)</tt></a></li>
    96. 

  96. <li><a class="reference internal" href="#boost-parameter-name-name" id="id75">7.19&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NAME(name)</tt></a></li>
    97. 

  97. <li><a class="reference internal" href="#boost-parameter-nested-keyword-tag-namespace-name-alias" id="id76">7.20&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NESTED_KEYWORD(tag_namespace, name, alias)</tt></a></li>
    98. 

  98. <li><a class="reference internal" href="#boost-parameter-template-keyword-name" id="id77">7.21&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_TEMPLATE_KEYWORD(name)</tt></a></li>
    99. 

  99. <li><a class="reference internal" href="#boost-parameter-fun-r-n-l-h-p" id="id78">7.22&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_FUN(r, n, l, h, p)</tt></a></li>
    100. 

  100. <li><a class="reference internal" href="#boost-parameter-keyword-n-k" id="id79">7.23&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_KEYWORD(n, k)</tt></a></li>
    101. 

  101. <li><a class="reference internal" href="#boost-parameter-match-p-a-x" id="id80">7.24&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_MATCH(p, a, x)</tt></a></li>
    102. 

  102. </ul>
    103. 

  103. </li>
    104. 

  104. <li><a class="reference internal" href="#configuration-macros" id="id81">8&nbsp;&nbsp;&nbsp;Configuration Macros</a><ul class="auto-toc">
    105. 

  105. <li><a class="reference internal" href="#id21" id="id82">8.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a></li>
    106. 

  106. <li><a class="reference internal" href="#id22" id="id83">8.2&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING</tt></a></li>
    107. 

  107. <li><a class="reference internal" href="#id23" id="id84">8.3&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a></li>
    108. 

  108. <li><a class="reference internal" href="#id24" id="id85">8.4&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_DISABLE_MP11_USAGE</tt></a></li>
    109. 

  109. <li><a class="reference internal" href="#id25" id="id86">8.5&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE</tt></a></li>
    110. 

  110. <li><a class="reference internal" href="#id26" id="id87">8.6&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_MAX_ARITY</tt></a></li>
    111. 

  111. <li><a class="reference internal" href="#id27" id="id88">8.7&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_COMPOSE_MAX_ARITY</tt></a></li>
    112. 

  112. <li><a class="reference internal" href="#id28" id="id89">8.8&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY</tt></a></li>
    113. 

  113. <li><a class="reference internal" href="#outside-of-this-library" id="id90">8.9&nbsp;&nbsp;&nbsp;...Outside Of This Library</a></li>
    114. 

  114. </ul>
    115. 

  115. </li>
    116. 

  116. <li><a class="reference internal" href="#tutorial" id="id91">9&nbsp;&nbsp;&nbsp;Tutorial</a></li>
    117. 

  117. </ul>
    118. 

  118. </div>
    119. 

  119. <hr class="docutils" />
    120. 

  120. <div class="section" id="preliminaries">
    121. 

  121. <h1><a class="toc-backref" href="#id31">1&nbsp;&nbsp;&nbsp;Preliminaries</a></h1>
    122. 

  122. <p>This section covers some basic information you'll need to know in order to
    123. 

  123. understand this reference.</p>
    124. 

  124. <div class="section" id="namespaces">
    125. 

  125. <h2><a class="toc-backref" href="#id32">1.1&nbsp;&nbsp;&nbsp;Namespaces</a></h2>
    126. 

  126. <p>In this document, all unqualified identifiers should be assumed to be defined
    127. 

  127. in namespace <tt class="docutils literal"><span class="pre">boost::parameter</span></tt> unless otherwise specified.</p>
    128. 

  128. </div>
    129. 

  129. <div class="section" id="exceptions">
    130. 

  130. <h2><a class="toc-backref" href="#id33">1.2&nbsp;&nbsp;&nbsp;Exceptions</a></h2>
    131. 

  131. <p>No operation described in this document throws an exception unless otherwise
    132. 

  132. specified.</p>
    133. 

  133. </div>
    134. 

  134. <div class="section" id="thread-safety">
    135. 

  135. <h2><a class="toc-backref" href="#id34">1.3&nbsp;&nbsp;&nbsp;Thread Safety</a></h2>
    136. 

  136. <p>All components of this library can be used safely from multiple threads
    137. 

  137. without synchronization.<a class="footnote-reference" href="#thread" id="id2"><sup>1</sup></a></p>
    138. 

  138. </div>
    139. 

  139. <div class="section" id="typography">
    140. 

  140. <h2><a class="toc-backref" href="#id35">1.4&nbsp;&nbsp;&nbsp;Typography</a></h2>
    141. 

  141. <p>Names written in <span class="concept">sans serif type</span> represent <a class="reference internal" href="#concepts">concepts</a>.</p>
    142. 

  142. <p>In code blocks, <em>italic type</em> represents unspecified text that satisfies the
    143. 

  143. requirements given in the detailed description that follows the code block.</p>
    144. 

  144. <p>In a specification of the tokens generated by a macro, <strong>bold type</strong> is used
    145. 

  145. to highlight the position of the expanded macro argument in the result.</p>
    146. 

  146. <p>The special character β represents the value of <a class="reference internal" href="#boost-parameter-max-arity"><tt class="docutils literal">BOOST_PARAMETER_MAX_ARITY</tt></a>.</p>
    147. 

  147. </div>
    148. 

  148. </div>
    149. 

  149. <hr class="docutils" />
    150. 

  150. <div class="section" id="terminology">
    151. 

  151. <h1><a class="toc-backref" href="#id36">2&nbsp;&nbsp;&nbsp;Terminology</a></h1>
    152. 

  152. <dl class="docutils" id="kw">
    153. 

  153. <dt>keyword</dt>
    154. 

  154. <dd>The name of a function parameter.</dd>
    155. 

  155. </dl>
    156. 

  156. <span class="target" id="keyword-tag-type"></span><dl class="docutils">
    157. 

  157. <dt>keyword tag type</dt>
    158. 

  158. <dd>A type used to uniquely identify a function parameter.  Typically its name
    159. 

  159. will be the same as that of the parameter.</dd>
    160. 

  160. </dl>
    161. 

  161. <span class="target" id="positional"></span><dl class="docutils">
    162. 

  162. <dt>positional argument</dt>
    163. 

  163. <dd>An argument passed with no explicit keyword.  Its parameter is determined
    164. 

  164. in the usual C++ way: by position with respect to a parameter list.</dd>
    165. 

  165. </dl>
    166. 

  166. <span class="target" id="tag-type"></span><dl class="docutils">
    167. 

  167. <dt>tag type</dt>
    168. 

  168. <dd>Shorthand for “<a class="reference internal" href="#keyword-tag-type">keyword tag type</a>.”</dd>
    169. 

  169. </dl>
    170. 

  170. <span class="target" id="keyword-object"></span><dl class="docutils">
    171. 

  171. <dt>keyword object</dt>
    172. 

  172. <dd>An instance of <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a><tt class="docutils literal">&lt;T&gt;</tt> for some <a class="reference internal" href="#tag-type">tag type</a> <tt class="docutils literal">T</tt>.</dd>
    173. 

  173. </dl>
    174. 

  174. <span class="target" id="tagged-reference"></span><dl class="docutils">
    175. 

  175. <dt>tagged reference</dt>
    176. 

  176. <dd><p class="first">An object whose type is associated with a <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> (the object's
    177. 

  177. <em>keyword</em>), and that holds a reference (to the object's <em>value</em>).</p>
    178. 

  178. <p class="last">As a shorthand, a “tagged reference to <tt class="docutils literal">x</tt>” means a tagged reference
    179. 

  179. whose <em>value</em> is <tt class="docutils literal">x</tt>.</p>
    180. 

  180. </dd>
    181. 

  181. </dl>
    182. 

  182. <span class="target" id="tagged-default"></span><dl class="docutils">
    183. 

  183. <dt>tagged default</dt>
    184. 

  184. <dd>A <a class="reference internal" href="#tagged-reference">tagged reference</a> whose <em>value</em> represents the value of a
    185. 

  185. default argument.</dd>
    186. 

  186. </dl>
    187. 

  187. <span class="target" id="tagged-lazy-default"></span><dl class="docutils">
    188. 

  188. <dt>tagged lazy default</dt>
    189. 

  189. <dd>A <a class="reference internal" href="#tagged-reference">tagged reference</a> whose <em>value</em>, when invoked with no arguments,
    190. 

  190. computes a default argument value.</dd>
    191. 

  191. </dl>
    192. 

  192. <span class="target" id="intended-argument-type"></span><dl class="docutils">
    193. 

  193. <dt>intended argument type</dt>
    194. 

  194. <dd>The <em>intended argument type</em> of a single-element <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> is the
    195. 

  195. type of its element's <em>value</em>.  The intended argument type of any other
    196. 

  196. type <tt class="docutils literal">X</tt> is <tt class="docutils literal">X</tt> itself.</dd>
    197. 

  197. </dl>
    198. 

  198. <div class="note">
    199. 

  199. <p class="first admonition-title">Note</p>
    200. 

  200. <p class="last">In this reference, we will use concept names (and other names) to describe
    201. 

  201. both types and objects, depending on context.  So for example, “an
    202. 

  202. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>” can refer to a type that models <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>
    203. 

  203. <em>or</em> an object of such a type.</p>
    204. 

  204. </div>
    205. 

  205. </div>
    206. 

  206. <hr class="docutils" />
    207. 

  207. <div class="section" id="concepts">
    208. 

  208. <h1><a class="toc-backref" href="#id37">3&nbsp;&nbsp;&nbsp;Concepts</a></h1>
    209. 

  209. <p>This section describes the generic type concepts used by the Parameter
    210. 

  210. library.</p>
    211. 

  211. <div class="section" id="argumentpack">
    212. 

  212. <h2><a class="toc-backref" href="#id38">3.1&nbsp;&nbsp;&nbsp;<span class="concept">ArgumentPack</span></a></h2>
    213. 

  213. <p>An <span class="concept">ArgumentPack</span> is a collection of <a class="reference internal" href="#tagged-reference">tagged reference</a>s to the actual
    214. 

  214. arguments passed to a function.  Every <span class="concept">ArgumentPack</span> is also a valid <a class="reference external" href="../../../mpl/doc/refmanual/forward-sequence.html">MPL
    215. 

  215. Forward Sequence</a> and <a class="reference external" href="../../../mpl/doc/refmanual/associative-sequence.html">MPL Associative Sequence</a> consisting of the <a class="reference internal" href="#keyword-tag-type">keyword tag type</a>s in its <a class="reference internal" href="#tagged-reference">tagged reference</a>s.  If <tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt>
    216. 

  216. is defined, then every <span class="concept">ArgumentPack</span> is also a valid <a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a> map whose
    217. 

  217. keys are <a class="reference internal" href="#keyword-tag-type">keyword tag type</a>s.  The <a class="reference external" href="../../test/singular.cpp">singular.cpp</a>, <a class="reference external" href="../../test/compose.cpp">compose.cpp</a>, and
    218. 

  218. <a class="reference external" href="../../test/mpl.cpp">mpl.cpp</a> test programs demonstrate this functionality.</p>
    219. 

  219. <div class="section" id="requirements">
    220. 

  220. <h3>Requirements</h3>
    221. 

  221. <p>In the table below,</p>
    222. 

  222. <ul class="simple">
    223. 

  223. <li><tt class="docutils literal">A</tt> is a model of <span class="concept">ArgumentPack</span></li>
    224. 

  224. <li><tt class="docutils literal">x</tt> is an instance of <tt class="docutils literal">A</tt></li>
    225. 

  225. <li><tt class="docutils literal">u</tt> is a <a class="reference internal" href="#keyword-object">keyword object</a> of type <tt class="docutils literal">K</tt></li>
    226. 

  226. <li><tt class="docutils literal">v</tt> is a <a class="reference internal" href="#tagged-default">tagged default</a> with <a class="reference internal" href="#tag-type">tag type</a> <tt class="docutils literal">L</tt> and <em>value</em> of type <tt class="docutils literal">D</tt></li>
    227. 

  227. <li><tt class="docutils literal">w</tt> is a <a class="reference internal" href="#tagged-lazy-default">tagged lazy default</a> with <a class="reference internal" href="#tag-type">tag type</a> <tt class="docutils literal">M</tt> and <em>value</em> of type <tt class="docutils literal">E const</tt></li>
    228. 

  228. <li><tt class="docutils literal">z</tt> is an <span class="concept">ArgumentPack</span> containing a single element (as created by <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a><tt class="docutils literal"><span class="pre">&lt;…&gt;::operator=</span></tt>)</li>
    229. 

  229. </ul>
    230. 

  230. <p>Any exceptions thrown from the invocation of <tt class="docutils literal">w</tt>'s <em>value</em>
    231. 

  231. will be propagated to the caller.</p>
    232. 

  232. <table border="1" class="docutils">
    233. 

  233. <caption><span class="concept">ArgumentPack</span> requirements</caption>
    234. 

  234. <colgroup>
    235. 

  235. <col width="14%" />
    236. 

  236. <col width="40%" />
    237. 

  237. <col width="19%" />
    238. 

  238. <col width="27%" />
    239. 

  239. </colgroup>
    240. 

  240. <thead valign="bottom">
    241. 

  241. <tr><th class="head">Expression</th>
    242. 

  242. <th class="head">Type</th>
    243. 

  243. <th class="head">Requirements</th>
    244. 

  244. <th class="head">Semantics/Notes</th>
    245. 

  245. </tr>
    246. 

  246. </thead>
    247. 

  247. <tbody valign="top">
    248. 

  248. <tr><td><tt class="docutils literal">x[u]</tt></td>
    249. 

  249. <td><tt class="docutils literal">binding&lt;A, <span class="pre">K&gt;::type</span></tt></td>
    250. 

  250. <td><tt class="docutils literal">x</tt> contains
    251. 

  251. an element <em>b</em>
    252. 

  252. whose <a class="reference internal" href="#kw">keyword</a> is
    253. 

  253. <tt class="docutils literal">K</tt></td>
    254. 

  254. <td>Returns <em>b</em>'s
    255. 

  255. <em>value</em> (by
    256. 

  256. reference).</td>
    257. 

  257. </tr>
    258. 

  258. <tr><td><tt class="docutils literal">x[u]</tt></td>
    259. 

  259. <td><tt class="docutils literal">binding&lt;A, L, <span class="pre">D&gt;::type</span></tt></td>
    260. 

  260. <td><em>none</em></td>
    261. 

  261. <td>If <tt class="docutils literal">x</tt> contains an
    262. 

  262. element <em>b</em> whose
    263. 

  263. <a class="reference internal" href="#kw">keyword</a> is the same as
    264. 

  264. <tt class="docutils literal">u</tt>'s, returns
    265. 

  265. <em>b</em>'s <em>value</em> (by
    266. 

  266. reference).
    267. 

  267. Otherwise, returns
    268. 

  268. <tt class="docutils literal">u</tt>'s <em>value</em>.</td>
    269. 

  269. </tr>
    270. 

  270. <tr><td><tt class="docutils literal">x[w]</tt></td>
    271. 

  271. <td><tt class="docutils literal">lazy_binding&lt;A, M, <span class="pre">E&gt;::type</span></tt></td>
    272. 

  272. <td><em>none</em></td>
    273. 

  273. <td>If <tt class="docutils literal">x</tt> contains an
    274. 

  274. element <em>b</em> whose
    275. 

  275. <a class="reference internal" href="#kw">keyword</a> is the same as
    276. 

  276. <tt class="docutils literal">w</tt>'s, returns
    277. 

  277. <em>b</em>'s <em>value</em> (by
    278. 

  278. reference).
    279. 

  279. Otherwise, invokes
    280. 

  280. <tt class="docutils literal">w</tt>'s <em>value</em>
    281. 

  281. and returns the
    282. 

  282. result.</td>
    283. 

  283. </tr>
    284. 

  284. <tr><td><tt class="docutils literal">x, z</tt></td>
    285. 

  285. <td>Model of <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a></td>
    286. 

  286. <td><em>none</em></td>
    287. 

  287. <td>Returns an
    288. 

  288. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>
    289. 

  289. containing all the
    290. 

  290. elements of both
    291. 

  291. <tt class="docutils literal">x</tt> and <tt class="docutils literal">z</tt>.</td>
    292. 

  292. </tr>
    293. 

  293. </tbody>
    294. 

  294. </table>
    295. 

  295. </div>
    296. 

  296. </div>
    297. 

  297. <div class="section" id="id3">
    298. 

  298. <span id="parameterspec"></span><h2><a class="toc-backref" href="#id39">3.2&nbsp;&nbsp;&nbsp;<span class="concept">ParameterSpec</span></a></h2>
    299. 

  299. <p>A <span class="concept">ParameterSpec</span> describes the type requirements for arguments corresponding
    300. 

  300. to a given <a class="reference internal" href="#kw">keyword</a> and indicates whether the argument is optional or
    301. 

  301. required.  The table below details the allowed forms and describes their
    302. 

  302. condition for satisfaction by an actual argument type. In each row,</p>
    303. 

  303. <ul class="simple" id="conditions">
    304. 

  304. <li><tt class="docutils literal">K</tt> is the <span class="concept">ParameterSpec</span>'s <a class="reference internal" href="#keyword-tag-type">keyword tag type</a></li>
    305. 

  305. <li><tt class="docutils literal">A</tt> is an <a class="reference internal" href="#intended-argument-type">intended argument type</a> associated with <tt class="docutils literal">K</tt>, if any</li>
    306. 

  306. <li><tt class="docutils literal">P</tt> is a model of <span class="concept">ArgumentPack</span> that contains <tt class="docutils literal">A</tt></li>
    307. 

  307. <li><tt class="docutils literal">F</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a></li>
    308. 

  308. </ul>
    309. 

  309. <table border="1" class="docutils">
    310. 

  310. <caption><span class="concept">ParameterSpec</span> allowed forms and conditions of satisfaction</caption>
    311. 

  311. <colgroup>
    312. 

  312. <col width="32%" />
    313. 

  313. <col width="14%" />
    314. 

  314. <col width="54%" />
    315. 

  315. </colgroup>
    316. 

  316. <thead valign="bottom">
    317. 

  317. <tr><th class="head">Type</th>
    318. 

  318. <th class="head"><tt class="docutils literal">A</tt>
    319. 

  319. required</th>
    320. 

  320. <th class="head">Condition <tt class="docutils literal">A</tt> must satisfy</th>
    321. 

  321. </tr>
    322. 

  322. </thead>
    323. 

  323. <tbody valign="top">
    324. 

  324. <tr><td><tt class="docutils literal">K</tt></td>
    325. 

  325. <td>no</td>
    326. 

  326. <td><em>n/a</em></td>
    327. 

  327. </tr>
    328. 

  328. <tr><td><a class="reference internal" href="#optional"><tt class="docutils literal">optional</tt></a><tt class="docutils literal">&lt;K,F&gt;</tt></td>
    329. 

  329. <td>no</td>
    330. 

  330. <td><tt class="docutils literal"><span class="pre">mpl::apply2&lt;F,A,P&gt;::type::value</span></tt> is
    331. 

  331. <tt class="docutils literal">true</tt>.</td>
    332. 

  332. </tr>
    333. 

  333. <tr><td><a class="reference internal" href="#required"><tt class="docutils literal">required</tt></a><tt class="docutils literal">&lt;K,F&gt;</tt></td>
    334. 

  334. <td>yes</td>
    335. 

  335. <td><tt class="docutils literal"><span class="pre">mpl::apply2&lt;F,A,P&gt;::type::value</span></tt> is
    336. 

  336. <tt class="docutils literal">true</tt>.</td>
    337. 

  337. </tr>
    338. 

  338. </tbody>
    339. 

  339. </table>
    340. 

  340. <p>The information in a <span class="concept">ParameterSpec</span> is used to <a class="reference external" href="index.html#controlling-overload-resolution">limit</a> the arguments that
    341. 

  341. will be matched by <a class="reference external" href="index.html#forwarding-functions">forwarding functions</a>.</p>
    342. 

  342. </div>
    343. 

  343. </div>
    344. 

  344. <hr class="docutils" />
    345. 

  345. <div class="section" id="class-templates">
    346. 

  346. <h1><a class="toc-backref" href="#id40">4&nbsp;&nbsp;&nbsp;Class Templates</a></h1>
    347. 

  347. <div class="section" id="id5">
    348. 

  348. <span id="keyword"></span><h2><a class="toc-backref" href="#id41">4.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">keyword</tt></a></h2>
    349. 

  349. <p>The type of every <a class="reference internal" href="#keyword-object">keyword object</a> is a specialization of <tt class="docutils literal">keyword</tt>.</p>
    350. 

  350. <table class="docutils field-list" frame="void" rules="none">
    351. 

  351. <col class="field-name" />
    352. 

  352. <col class="field-body" />
    353. 

  353. <tbody valign="top">
    354. 

  354. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/keyword.hpp">boost/parameter/keyword.hpp</a></td>
    355. 

  355. </tr>
    356. 

  356. </tbody>
    357. 

  357. </table>
    358. 

  358. <pre class="literal-block">
    359. 

  359. template &lt;typename Tag&gt;
    360. 

  360. struct keyword
    361. 

  361. {
    362. 

  362.     typedef Tag tag;
    363. 

  363. 

  364.     template &lt;typename T&gt;
    365. 

  365.     constexpr typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    366. 

  366.         typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    367. 

  367.             <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_scalar.html">boost::is_scalar</a>&lt;T&gt;
    368. 

  368.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for scalar types.
    369. 

  369.           , <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    370. 

  370.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    371. 

  371.                     typename Tag::qualifier
    372. 

  372.                   , boost::parameter::in_reference
    373. 

  373.                 &gt;
    374. 

  374.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;in&quot; references.
    375. 

  375.               , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    376. 

  376.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    377. 

  377.                         typename Tag::qualifier
    378. 

  378.                       , boost::parameter::forward_reference
    379. 

  379.                     &gt;
    380. 

  380.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;forward&quot; references.
    381. 

  381.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for all other reference categories.
    382. 

  382.                 &gt;
    383. 

  383.             &gt;
    384. 

  384.         &gt;::type
    385. 

  385.       , <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>
    386. 

  386.     &gt;::type
    387. 

  387.         <a class="reference internal" href="#assignment-operator"><tt class="docutils literal">operator=</tt></a>(T const&amp; value) const;
    388. 

  388. 

  389.     template &lt;typename T&gt;
    390. 

  390.     constexpr typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    391. 

  391.         typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    392. 

  392.             typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    393. 

  393.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    394. 

  394.                     typename Tag::qualifier
    395. 

  395.                   , boost::parameter::out_reference
    396. 

  396.                 &gt;
    397. 

  397.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // The reference category is &quot;out&quot;.
    398. 

  398.               , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    399. 

  399.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    400. 

  400.                         typename Tag::qualifier
    401. 

  401.                       , boost::parameter::forward_reference
    402. 

  402.                     &gt;
    403. 

  403.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // The reference category is &quot;forward&quot;.
    404. 

  404.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // The reference category is neither &quot;out&quot; nor &quot;forward&quot;.
    405. 

  405.                 &gt;
    406. 

  406.             &gt;::type
    407. 

  407.           , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    408. 

  408.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_const.html">boost::is_const</a>&lt;T&gt;
    409. 

  409.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for reference-to-const types.
    410. 

  410.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for referece-to-mutable types.
    411. 

  411.             &gt;
    412. 

  412.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for references neither &quot;out&quot; nor &quot;forward&quot;.
    413. 

  413.         &gt;::type
    414. 

  414.       , <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>
    415. 

  415.     &gt;::type
    416. 

  416.         <a class="reference internal" href="#assignment-operator"><tt class="docutils literal">operator=</tt></a>(T&amp; value) const;
    417. 

  417. 

  418.     template &lt;typename T&gt;
    419. 

  419.     constexpr typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    420. 

  420.         typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    421. 

  421.             <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_scalar.html">boost::is_scalar</a>&lt;T&gt;
    422. 

  422.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for scalar types.
    423. 

  423.           , <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    424. 

  424.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    425. 

  425.                     typename Tag::qualifier
    426. 

  426.                   , boost::parameter::in_reference
    427. 

  427.                 &gt;
    428. 

  428.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;in&quot; references.
    429. 

  429.               , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    430. 

  430.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    431. 

  431.                         typename Tag::qualifier
    432. 

  432.                       , boost::parameter::forward_reference
    433. 

  433.                     &gt;
    434. 

  434.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;forward&quot; references.
    435. 

  435.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for all other reference categories.
    436. 

  436.                 &gt;
    437. 

  437.             &gt;
    438. 

  438.         &gt;::type
    439. 

  439.       , <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>
    440. 

  440.     &gt;::type
    441. 

  441.         <a class="reference internal" href="#assignment-operator"><tt class="docutils literal">operator=</tt></a>(T const&amp;&amp; value) const;
    442. 

  442. 

  443.     template &lt;typename T&gt;
    444. 

  444.     constexpr typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    445. 

  445.         typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    446. 

  446.             <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_scalar.html">boost::is_scalar</a>&lt;T&gt;
    447. 

  447.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for scalar types.
    448. 

  448.           , <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    449. 

  449.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    450. 

  450.                     typename Tag::qualifier
    451. 

  451.                   , boost::parameter::consume_reference
    452. 

  452.                 &gt;
    453. 

  453.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;consume&quot; references.
    454. 

  454.               , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    455. 

  455.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    456. 

  456.                         typename Tag::qualifier
    457. 

  457.                       , boost::parameter::forward_reference
    458. 

  458.                     &gt;
    459. 

  459.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;forward&quot; references.
    460. 

  460.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for all other reference categories.
    461. 

  461.                 &gt;
    462. 

  462.             &gt;
    463. 

  463.         &gt;::type
    464. 

  464.       , <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>
    465. 

  465.     &gt;::type
    466. 

  466.         <a class="reference internal" href="#assignment-operator"><tt class="docutils literal">operator=</tt></a>(T&amp;&amp; value) const;
    467. 

  467. 

  468.     template &lt;typename T&gt;
    469. 

  469.     constexpr typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    470. 

  470.         typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    471. 

  471.             <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_scalar.html">boost::is_scalar</a>&lt;T&gt;
    472. 

  472.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for scalar types.
    473. 

  473.           , <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    474. 

  474.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    475. 

  475.                     typename Tag::qualifier
    476. 

  476.                   , boost::parameter::in_reference
    477. 

  477.                 &gt;
    478. 

  478.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;in&quot; references.
    479. 

  479.               , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    480. 

  480.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    481. 

  481.                         typename Tag::qualifier
    482. 

  482.                       , boost::parameter::forward_reference
    483. 

  483.                     &gt;
    484. 

  484.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;forward&quot; references.
    485. 

  485.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for all other reference categories.
    486. 

  486.                 &gt;
    487. 

  487.             &gt;
    488. 

  488.         &gt;::type
    489. 

  489.       , <em>tagged default</em>
    490. 

  490.     &gt;::type
    491. 

  491.         <a class="reference internal" href="#bitwise-or-operator"><tt class="docutils literal">operator|</tt></a>(T const&amp; x) const;
    492. 

  492. 

  493.     template &lt;typename T&gt;
    494. 

  494.     constexpr typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    495. 

  495.         typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    496. 

  496.             typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    497. 

  497.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    498. 

  498.                     typename Tag::qualifier
    499. 

  499.                   , boost::parameter::out_reference
    500. 

  500.                 &gt;
    501. 

  501.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // The reference category is &quot;out&quot;.
    502. 

  502.               , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    503. 

  503.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    504. 

  504.                         typename Tag::qualifier
    505. 

  505.                       , boost::parameter::forward_reference
    506. 

  506.                     &gt;
    507. 

  507.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // The reference category is &quot;forward&quot;.
    508. 

  508.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // The reference category is neither &quot;out&quot; nor &quot;forward&quot;.
    509. 

  509.                 &gt;
    510. 

  510.             &gt;::type
    511. 

  511.           , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    512. 

  512.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_const.html">boost::is_const</a>&lt;T&gt;
    513. 

  513.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for reference-to-const types.
    514. 

  514.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for referece-to-mutable types.
    515. 

  515.             &gt;
    516. 

  516.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for references neither &quot;out&quot; nor &quot;forward&quot;.
    517. 

  517.         &gt;::type
    518. 

  518.       , <em>tagged default</em>
    519. 

  519.     &gt;::type
    520. 

  520.         <a class="reference internal" href="#bitwise-or-operator"><tt class="docutils literal">operator|</tt></a>(T&amp; x) const;
    521. 

  521. 

  522.     template &lt;typename T&gt;
    523. 

  523.     constexpr typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    524. 

  524.         typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    525. 

  525.             <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_scalar.html">boost::is_scalar</a>&lt;T&gt;
    526. 

  526.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for scalar types.
    527. 

  527.           , <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    528. 

  528.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    529. 

  529.                     typename Tag::qualifier
    530. 

  530.                   , boost::parameter::in_reference
    531. 

  531.                 &gt;
    532. 

  532.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;in&quot; references.
    533. 

  533.               , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    534. 

  534.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    535. 

  535.                         typename Tag::qualifier
    536. 

  536.                       , boost::parameter::forward_reference
    537. 

  537.                     &gt;
    538. 

  538.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;forward&quot; references.
    539. 

  539.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for all other reference categories.
    540. 

  540.                 &gt;
    541. 

  541.             &gt;
    542. 

  542.         &gt;::type
    543. 

  543.       , <em>tagged default</em>
    544. 

  544.     &gt;::type
    545. 

  545.         <a class="reference internal" href="#bitwise-or-operator"><tt class="docutils literal">operator|</tt></a>(T const&amp;&amp; x) const;
    546. 

  546. 

  547.     template &lt;typename T&gt;
    548. 

  548.     constexpr typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    549. 

  549.         typename <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    550. 

  550.             <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_scalar.html">boost::is_scalar</a>&lt;T&gt;
    551. 

  551.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for scalar types.
    552. 

  552.           , <a class="reference external" href="../../../mpl/doc/refmanual/eval-if.html">boost::mpl::eval_if</a>&lt;
    553. 

  553.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    554. 

  554.                     typename Tag::qualifier
    555. 

  555.                   , boost::parameter::consume_reference
    556. 

  556.                 &gt;
    557. 

  557.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;consume&quot; references.
    558. 

  558.               , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    559. 

  559.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    560. 

  560.                         typename Tag::qualifier
    561. 

  561.                       , boost::parameter::forward_reference
    562. 

  562.                     &gt;
    563. 

  563.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> // Enable this overload for &quot;forward&quot; references.
    564. 

  564.                   , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // Disable this overload for all other reference categories.
    565. 

  565.                 &gt;
    566. 

  566.             &gt;
    567. 

  567.         &gt;::type
    568. 

  568.       , <em>tagged default</em>
    569. 

  569.     &gt;::type constexpr
    570. 

  570.         <a class="reference internal" href="#bitwise-or-operator"><tt class="docutils literal">operator|</tt></a>(T&amp;&amp; value) const;
    571. 

  571. 

  572.     template &lt;typename F&gt;
    573. 

  573.     constexpr <em>tagged lazy default</em> <a class="reference internal" href="#logical-or-operator"><tt class="docutils literal">operator||</tt></a>(F const&amp;) const;
    574. 

  574. 

  575.     template &lt;typename F&gt;
    576. 

  576.     constexpr <em>tagged lazy default</em> <a class="reference internal" href="#logical-or-operator"><tt class="docutils literal">operator||</tt></a>(F&amp;) const;
    577. 

  577. 

  578.     static keyword&lt;Tag&gt; const&amp; instance;
    579. 

  579. 

  580.     static keyword&lt;Tag&gt;&amp; <a class="reference internal" href="#get">get</a>();
    581. 

  581. };
    582. 

  582. </pre>
    583. 

  583. <p id="assignment-operator"><tt class="docutils literal">operator=</tt></p>
    584. 

  584. <table class="docutils field-list" frame="void" rules="none">
    585. 

  585. <col class="field-name" />
    586. 

  586. <col class="field-body" />
    587. 

  587. <tbody valign="top">
    588. 

  588. <tr class="field"><th class="field-name">Synopsis:</th><td class="field-body"></td>
    589. 

  589. </tr>
    590. 

  590. </tbody>
    591. 

  591. </table>
    592. 

  592. <pre class="literal-block">
    593. 

  593. template &lt;typename T&gt;
    594. 

  594. constexpr <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> operator=(T const&amp; value) const;
    595. 

  595. 

  596. template &lt;typename T&gt;
    597. 

  597. constexpr <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> operator=(T&amp; value) const;
    598. 

  598. 

  599. template &lt;typename T&gt;
    600. 

  600. constexpr <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> operator=(T const&amp;&amp; value) const;
    601. 

  601. 

  602. template &lt;typename T&gt;
    603. 

  603. constexpr <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> operator=(T&amp;&amp; value) const;
    604. 

  604. </pre>
    605. 

  605. <table class="docutils field-list" frame="void" rules="none">
    606. 

  606. <col class="field-name" />
    607. 

  607. <col class="field-body" />
    608. 

  608. <tbody valign="top">
    609. 

  609. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">one of the following:</td>
    610. 

  610. </tr>
    611. 

  611. </tbody>
    612. 

  612. </table>
    613. 

  613. <ul class="simple">
    614. 

  614. <li>The nested <tt class="docutils literal">qualifier</tt> type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">forward_reference</tt>.</li>
    615. 

  615. <li>To use the <tt class="docutils literal">const</tt> lvalue reference overload, <tt class="docutils literal">T</tt> must be scalar, or
    616. 

  616. the nested <tt class="docutils literal">qualifier</tt> type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">in_reference</tt>.</li>
    617. 

  617. <li>To use the mutable lvalue reference overload, the nested <tt class="docutils literal">qualifier</tt>
    618. 

  618. type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">out_reference</tt> or <tt class="docutils literal">in_out_reference</tt>, and
    619. 

  619. <tt class="docutils literal">T</tt> must not be <tt class="docutils literal">const</tt>-qualified.</li>
    620. 

  620. <li>To use the <tt class="docutils literal">const</tt> rvalue reference overload for non-scalar <tt class="docutils literal">T</tt>, the
    621. 

  621. nested <tt class="docutils literal">qualifier</tt> type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">in_reference</tt>.</li>
    622. 

  622. <li>To use the mutable rvalue reference overload for non-scalar <tt class="docutils literal">T</tt>, the
    623. 

  623. nested <tt class="docutils literal">qualifier</tt> type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">consume_reference</tt> or
    624. 

  624. <tt class="docutils literal">move_from_reference</tt>.</li>
    625. 

  625. </ul>
    626. 

  626. <table class="docutils field-list" frame="void" rules="none">
    627. 

  627. <col class="field-name" />
    628. 

  628. <col class="field-body" />
    629. 

  629. <tbody valign="top">
    630. 

  630. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">an <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>  containing a single <a class="reference internal" href="#tagged-reference">tagged reference</a> to
    631. 

  631. <tt class="docutils literal">value</tt> with <a class="reference internal" href="#kw">keyword</a> <tt class="docutils literal">Tag</tt></td>
    632. 

  632. </tr>
    633. 

  633. </tbody>
    634. 

  634. </table>
    635. 

  635. <p id="bitwise-or-operator"><tt class="docutils literal">operator|</tt></p>
    636. 

  636. <table class="docutils field-list" frame="void" rules="none">
    637. 

  637. <col class="field-name" />
    638. 

  638. <col class="field-body" />
    639. 

  639. <tbody valign="top">
    640. 

  640. <tr class="field"><th class="field-name">Synopsis:</th><td class="field-body"></td>
    641. 

  641. </tr>
    642. 

  642. </tbody>
    643. 

  643. </table>
    644. 

  644. <pre class="literal-block">
    645. 

  645. template &lt;typename T&gt;
    646. 

  646. constexpr <em>tagged default</em> operator|(T const&amp; x) const;
    647. 

  647. 

  648. template &lt;typename T&gt;
    649. 

  649. constexpr <em>tagged default</em> operator|(T&amp; x) const;
    650. 

  650. 

  651. template &lt;typename T&gt;
    652. 

  652. constexpr <em>tagged default</em> operator|(T const&amp;&amp; x) const;
    653. 

  653. 

  654. template &lt;typename T&gt;
    655. 

  655. constexpr <em>tagged default</em> operator|(T&amp;&amp; x) const;
    656. 

  656. </pre>
    657. 

  657. <table class="docutils field-list" frame="void" rules="none">
    658. 

  658. <col class="field-name" />
    659. 

  659. <col class="field-body" />
    660. 

  660. <tbody valign="top">
    661. 

  661. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">one of the following:</td>
    662. 

  662. </tr>
    663. 

  663. </tbody>
    664. 

  664. </table>
    665. 

  665. <ul class="simple">
    666. 

  666. <li>The nested <tt class="docutils literal">qualifier</tt> type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">forward_reference</tt>.</li>
    667. 

  667. <li>To use the <tt class="docutils literal">const</tt> lvalue reference overload, <tt class="docutils literal">T</tt> must be scalar, or
    668. 

  668. the nested <tt class="docutils literal">qualifier</tt> type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">in_reference</tt>.</li>
    669. 

  669. <li>To use the mutable lvalue reference overload, the nested <tt class="docutils literal">qualifier</tt>
    670. 

  670. type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">out_reference</tt> or <tt class="docutils literal">in_out_reference</tt>, and
    671. 

  671. <tt class="docutils literal">T</tt> must not be <tt class="docutils literal">const</tt>-qualified.</li>
    672. 

  672. <li>To use the <tt class="docutils literal">const</tt> rvalue reference overload for non-scalar <tt class="docutils literal">T</tt>, the
    673. 

  673. nested <tt class="docutils literal">qualifier</tt> type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">in_reference</tt>.</li>
    674. 

  674. <li>To use the mutable rvalue reference overload for non-scalar <tt class="docutils literal">T</tt>, the
    675. 

  675. nested <tt class="docutils literal">qualifier</tt> type of <tt class="docutils literal">Tag</tt> must be <tt class="docutils literal">consume_reference</tt> or
    676. 

  676. <tt class="docutils literal">move_from_reference</tt>.</li>
    677. 

  677. </ul>
    678. 

  678. <table class="docutils field-list" frame="void" rules="none">
    679. 

  679. <col class="field-name" />
    680. 

  680. <col class="field-body" />
    681. 

  681. <tbody valign="top">
    682. 

  682. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">a <a class="reference internal" href="#tagged-default">tagged default</a> with <em>value</em> <tt class="docutils literal">x</tt> and <a class="reference internal" href="#kw">keyword</a> <tt class="docutils literal">Tag</tt>.</td>
    683. 

  683. </tr>
    684. 

  684. </tbody>
    685. 

  685. </table>
    686. 

  686. <p id="logical-or-operator"><tt class="docutils literal">operator||</tt></p>
    687. 

  687. <table class="docutils field-list" frame="void" rules="none">
    688. 

  688. <col class="field-name" />
    689. 

  689. <col class="field-body" />
    690. 

  690. <tbody valign="top">
    691. 

  691. <tr class="field"><th class="field-name">Synopsis:</th><td class="field-body"></td>
    692. 

  692. </tr>
    693. 

  693. </tbody>
    694. 

  694. </table>
    695. 

  695. <pre class="literal-block">
    696. 

  696. template &lt;typename F&gt;
    697. 

  697. constexpr <em>tagged lazy default</em> operator||(F const&amp; g) const;
    698. 

  698. 

  699. template &lt;typename F&gt;
    700. 

  700. constexpr <em>tagged lazy default</em> operator||(F&amp; g) const;
    701. 

  701. </pre>
    702. 

  702. <table class="docutils field-list" frame="void" rules="none">
    703. 

  703. <col class="field-name" />
    704. 

  704. <col class="field-body" />
    705. 

  705. <tbody valign="top">
    706. 

  706. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal">g()</tt> must be valid, with type
    707. 

  707. <a class="reference external" href="../../../utility/utility.htm#result_of"><tt class="docutils literal"><span class="pre">boost::result_of</span></tt></a><tt class="docutils literal"><span class="pre">&lt;F()&gt;::type</span></tt>.<a class="footnote-reference" href="#no-result-of" id="id6"><sup>2</sup></a></td>
    708. 

  708. </tr>
    709. 

  709. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">a <a class="reference internal" href="#tagged-lazy-default">tagged lazy default</a> with <em>value</em> <tt class="docutils literal">g</tt> and <a class="reference internal" href="#kw">keyword</a> <tt class="docutils literal">Tag</tt>.</td>
    710. 

  710. </tr>
    711. 

  711. </tbody>
    712. 

  712. </table>
    713. 

  713. <p id="instance"><tt class="docutils literal">instance</tt></p>
    714. 

  714. <table class="docutils field-list" frame="void" rules="none">
    715. 

  715. <col class="field-name" />
    716. 

  716. <col class="field-body" />
    717. 

  717. <tbody valign="top">
    718. 

  718. <tr class="field"><th class="field-name">Synopsis:</th><td class="field-body"></td>
    719. 

  719. </tr>
    720. 

  720. </tbody>
    721. 

  721. </table>
    722. 

  722. <pre class="literal-block">
    723. 

  723. static keyword&lt;Tag&gt; const&amp; instance;
    724. 

  724. </pre>
    725. 

  725. <table class="docutils field-list" frame="void" rules="none">
    726. 

  726. <col class="field-name" />
    727. 

  727. <col class="field-body" />
    728. 

  728. <tbody valign="top">
    729. 

  729. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">a “singleton instance”: the same object will be returned on each
    730. 

  730. invocation of <tt class="docutils literal">instance</tt>.</td>
    731. 

  731. </tr>
    732. 

  732. <tr class="field"><th class="field-name">Thread Safety:</th><td class="field-body"><tt class="docutils literal">instance</tt> can be accessed from multiple threads simultaneously.</td>
    733. 

  733. </tr>
    734. 

  734. </tbody>
    735. 

  735. </table>
    736. 

  736. <p id="get"><tt class="docutils literal">get</tt></p>
    737. 

  737. <table class="docutils field-list" frame="void" rules="none">
    738. 

  738. <col class="field-name" />
    739. 

  739. <col class="field-body" />
    740. 

  740. <tbody valign="top">
    741. 

  741. <tr class="field"><th class="field-name">Synopsis:</th><td class="field-body"></td>
    742. 

  742. </tr>
    743. 

  743. </tbody>
    744. 

  744. </table>
    745. 

  745. <pre class="literal-block">
    746. 

  746. static keyword&lt;Tag&gt;&amp; get();
    747. 

  747. </pre>
    748. 

  748. <div class="admonition-deprecated admonition">
    749. 

  749. <p class="first admonition-title">Deprecated</p>
    750. 

  750. <p class="last">This function has been deprecated in favor of <tt class="docutils literal">instance</tt>.</p>
    751. 

  751. </div>
    752. 

  752. <table class="docutils field-list" frame="void" rules="none">
    753. 

  753. <col class="field-name" />
    754. 

  754. <col class="field-body" />
    755. 

  755. <tbody valign="top">
    756. 

  756. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">a “singleton instance”: the same object will be returned on each
    757. 

  757. invocation of <tt class="docutils literal">get()</tt>.</td>
    758. 

  758. </tr>
    759. 

  759. <tr class="field"><th class="field-name">Thread Safety:</th><td class="field-body"><tt class="docutils literal">get()</tt> can be called from multiple threads simultaneously.</td>
    760. 

  760. </tr>
    761. 

  761. </tbody>
    762. 

  762. </table>
    763. 

  763. </div>
    764. 

  764. <div class="section" id="id7">
    765. 

  765. <span id="template-keyword"></span><h2><a class="toc-backref" href="#id42">4.2&nbsp;&nbsp;&nbsp;<tt class="docutils literal">template_keyword</tt></a></h2>
    766. 

  766. <p>This class template encapsulates a named template parameter.  Every type
    767. 

  767. generated by the <a class="reference internal" href="#boost-parameter-template-keyword"><tt class="docutils literal">BOOST_PARAMETER_TEMPLATE_KEYWORD</tt></a> macro is a specialization
    768. 

  768. of <tt class="docutils literal">template_keyword</tt>.</p>
    769. 

  769. <table class="docutils field-list" frame="void" rules="none">
    770. 

  770. <col class="field-name" />
    771. 

  771. <col class="field-body" />
    772. 

  772. <tbody valign="top">
    773. 

  773. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/template_keyword.hpp">boost/parameter/template_keyword.hpp</a></td>
    774. 

  774. </tr>
    775. 

  775. </tbody>
    776. 

  776. </table>
    777. 

  777. <pre class="literal-block">
    778. 

  778. template &lt;typename Tag, typename T&gt;
    779. 

  779. struct template_keyword
    780. 

  780. {
    781. 

  781.     typedef Tag key_type;
    782. 

  782.     typedef T value_type;
    783. 

  783.     typedef <em>implementation defined</em> reference;
    784. 

  784. };
    785. 

  785. </pre>
    786. 

  786. <p>The <a class="reference external" href="../../test/ntp.cpp">test/ntp.cpp</a> test program demonstrates proper usage of this class template.</p>
    787. 

  787. </div>
    788. 

  788. <div class="section" id="id8">
    789. 

  789. <span id="parameters"></span><h2><a class="toc-backref" href="#id43">4.3&nbsp;&nbsp;&nbsp;<tt class="docutils literal">parameters</tt></a></h2>
    790. 

  790. <p>Provides an interface for assembling the actual arguments to a <cite>forwarding
    791. 

  791. function</cite> into an <span class="concept">ArgumentPack</span>, in which any <a class="reference internal" href="#positional">positional</a> arguments will be
    792. 

  792. tagged according to the corresponding template argument to <tt class="docutils literal">parameters</tt>.</p>
    793. 

  793. <table class="docutils field-list" frame="void" rules="none">
    794. 

  794. <col class="field-name" />
    795. 

  795. <col class="field-body" />
    796. 

  796. <tbody valign="top">
    797. 

  797. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/parameters.hpp">boost/parameter/parameters.hpp</a></td>
    798. 

  798. </tr>
    799. 

  799. </tbody>
    800. 

  800. </table>
    801. 

  801. <pre class="literal-block">
    802. 

  802. template &lt;typename ...PSpec&gt;
    803. 

  803. struct parameters
    804. 

  804. {
    805. 

  805.     template &lt;typename ...Args&gt;
    806. 

  806.     struct <a class="reference internal" href="#match"><tt class="docutils literal">match</tt></a>
    807. 

  807.     {
    808. 

  808.         typedef … type;
    809. 

  809.     };
    810. 

  810. 

  811.     template &lt;typename ...Args&gt;
    812. 

  812.     <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> <a class="reference internal" href="#function-call-operator"><tt class="docutils literal">operator()</tt></a>(Args&amp;&amp;... args) const;
    813. 

  813. };
    814. 

  814. </pre>
    815. 

  815. <table class="docutils field-list" frame="void" rules="none">
    816. 

  816. <col class="field-name" />
    817. 

  817. <col class="field-body" />
    818. 

  818. <tbody valign="top">
    819. 

  819. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">Each element in the <tt class="docutils literal">PSpec</tt> parameter pack must be a model of
    820. 

  820. <a class="reference internal" href="#parameterspec"><span class="concept">ParameterSpec</span></a>.</td>
    821. 

  821. </tr>
    822. 

  822. </tbody>
    823. 

  823. </table>
    824. 

  824. <div class="note">
    825. 

  825. <p class="first admonition-title">Note</p>
    826. 

  826. <p>In this section, <tt class="docutils literal">R</tt> ## <em>i</em> and <tt class="docutils literal">K</tt> ## <em>i</em> are defined as
    827. 

  827. follows, for any argument type <tt class="docutils literal">A</tt> ## <em>i</em>:</p>
    828. 

  828. <div class="last line-block">
    829. 

  829. <div class="line">let <tt class="docutils literal">D0</tt> the set [d0, …, d ## <em>j</em>] of all <strong>deduced</strong></div>
    830. 

  830. <div class="line"><em>parameter specs</em> in the <tt class="docutils literal">PSpec</tt> parameter pack</div>
    831. 

  831. <div class="line"><tt class="docutils literal">R</tt> ## <em>i</em> is the <a class="reference internal" href="#intended-argument-type">intended argument type</a> of <tt class="docutils literal">A</tt> ## <em>i</em></div>
    832. 

  832. <div class="line"><br /></div>
    833. 

  833. <div class="line">if <tt class="docutils literal">A</tt> ## <em>i</em> is a result type of <tt class="docutils literal"><span class="pre">keyword&lt;T&gt;::</span></tt> <a class="reference internal" href="#assignment-operator"><tt class="docutils literal">operator=</tt></a></div>
    834. 

  834. <div class="line">then</div>
    835. 

  835. <div class="line-block">
    836. 

  836. <div class="line"><tt class="docutils literal">K</tt> ## <em>i</em> is <tt class="docutils literal">T</tt></div>
    837. 

  837. </div>
    838. 

  838. <div class="line">else</div>
    839. 

  839. <div class="line-block">
    840. 

  840. <div class="line">if some <tt class="docutils literal">A</tt> ## <em>j</em> where <em>j</em> ≤ <em>i</em> is a result type of</div>
    841. 

  841. <div class="line"><tt class="docutils literal"><span class="pre">keyword&lt;T&gt;::</span></tt> <a class="reference internal" href="#assignment-operator"><tt class="docutils literal">operator=</tt></a></div>
    842. 

  842. <div class="line"><em>or</em> some <tt class="docutils literal">P</tt> ## <em>j</em> in <em>j</em> ≤ <em>i</em> is <strong>deduced</strong></div>
    843. 

  843. <div class="line">then</div>
    844. 

  844. <div class="line-block">
    845. 

  845. <div class="line">if some <em>parameter spec</em> <tt class="docutils literal">d</tt> ## <em>j</em> in <tt class="docutils literal">D</tt> ## <em>i</em></div>
    846. 

  846. <div class="line">matches <tt class="docutils literal">A</tt> ## <em>i</em></div>
    847. 

  847. <div class="line">then</div>
    848. 

  848. <div class="line-block">
    849. 

  849. <div class="line"><tt class="docutils literal">K</tt> ## <em>i</em> is the <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> of <tt class="docutils literal">d</tt> ## <em>j</em>.</div>
    850. 

  850. <div class="line"><tt class="docutils literal">D</tt><sub>i+1</sub> is <tt class="docutils literal">D</tt> ## <em>i</em> - [ <tt class="docutils literal">d</tt> ## <em>j</em>]</div>
    851. 

  851. </div>
    852. 

  852. </div>
    853. 

  853. <div class="line">else</div>
    854. 

  854. <div class="line-block">
    855. 

  855. <div class="line"><tt class="docutils literal">K</tt> ## <em>i</em> is the <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> of <tt class="docutils literal">P</tt> ## <em>i</em>.</div>
    856. 

  856. </div>
    857. 

  857. </div>
    858. 

  858. </div>
    859. 

  859. </div>
    860. 

  860. <dl class="docutils" id="match">
    861. 

  861. <dt><tt class="docutils literal">match</tt></dt>
    862. 

  862. <dd>A <a class="reference external" href="../../../mpl/doc/refmanual/metafunction.html">Metafunction</a> used to remove a <a class="reference external" href="index.html#forwarding-functions">forwarding function</a> from overload
    863. 

  863. resolution.</dd>
    864. 

  864. </dl>
    865. 

  865. <table class="docutils field-list" frame="void" rules="none">
    866. 

  866. <col class="field-name" />
    867. 

  867. <col class="field-body" />
    868. 

  868. <tbody valign="top">
    869. 

  869. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">if all elements in <tt class="docutils literal"><span class="pre">Params...</span></tt> are <em>satisfied</em> (see below), then
    870. 

  870. <tt class="docutils literal"><span class="pre">parameters&lt;Params...&gt;</span></tt>.  Otherwise, <tt class="docutils literal"><span class="pre">match&lt;Args...&gt;::type</span></tt> is not
    871. 

  871. defined.</td>
    872. 

  872. </tr>
    873. 

  873. </tbody>
    874. 

  874. </table>
    875. 

  875. <p>Each element <tt class="docutils literal">P</tt> in <tt class="docutils literal"><span class="pre">Params...</span></tt> is <strong>satisfied</strong> if either:</p>
    876. 

  876. <ul>
    877. 

  877. <li><p class="first"><tt class="docutils literal">P</tt> is the <em>unspecified</em> default</p>
    878. 

  878. </li>
    879. 

  879. <li><p class="first"><strong>or</strong>, <tt class="docutils literal">P</tt> is a <em>keyword tag type</em></p>
    880. 

  880. </li>
    881. 

  881. <li><dl class="first docutils">
    882. 

  882. <dt><strong>or</strong>, <tt class="docutils literal">P</tt> is <a class="reference internal" href="#optional"><tt class="docutils literal">optional</tt></a> <tt class="docutils literal">&lt;X,F&gt;</tt> and either</dt>
    883. 

  883. <dd><ul class="first last">
    884. 

  884. <li><p class="first"><tt class="docutils literal">X</tt> is not <tt class="docutils literal">K</tt> ## <em>i</em> for any <em>i</em>,</p>
    885. 

  885. </li>
    886. 

  886. <li><dl class="first docutils">
    887. 

  887. <dt><strong>or</strong> <tt class="docutils literal">X</tt> is some <tt class="docutils literal">K</tt> ## <em>i</em>  and <tt class="docutils literal"><span class="pre">mpl::apply&lt;F,R</span></tt> ## <em>i</em></dt>
    888. 

  888. <dd><p class="first last"><tt class="docutils literal"><span class="pre">&gt;::type::value</span></tt> is <tt class="docutils literal">true</tt></p>
    889. 

  889. </dd>
    890. 

  890. </dl>
    891. 

  891. </li>
    892. 

  892. </ul>
    893. 

  893. </dd>
    894. 

  894. </dl>
    895. 

  895. </li>
    896. 

  896. <li><dl class="first docutils">
    897. 

  897. <dt><strong>or</strong>, <tt class="docutils literal">P</tt> is <a class="reference internal" href="#required"><tt class="docutils literal">required</tt></a> <tt class="docutils literal">&lt;X,F&gt;</tt>, and</dt>
    898. 

  898. <dd><ul class="first last simple">
    899. 

  899. <li><tt class="docutils literal">X</tt> is some <tt class="docutils literal">K</tt> ## <em>i</em>, <strong>and</strong></li>
    900. 

  900. <li><tt class="docutils literal"><span class="pre">mpl::apply&lt;F,R</span></tt> ## <em>i</em> <tt class="docutils literal"><span class="pre">&gt;::type::value</span></tt> is <tt class="docutils literal">true</tt></li>
    901. 

  901. </ul>
    902. 

  902. </dd>
    903. 

  903. </dl>
    904. 

  904. </li>
    905. 

  905. </ul>
    906. 

  906. <p id="function-call-operator"><tt class="docutils literal">operator()</tt></p>
    907. 

  907. <table class="docutils field-list" frame="void" rules="none">
    908. 

  908. <col class="field-name" />
    909. 

  909. <col class="field-body" />
    910. 

  910. <tbody valign="top">
    911. 

  911. <tr class="field"><th class="field-name">Synopsis:</th><td class="field-body"></td>
    912. 

  912. </tr>
    913. 

  913. </tbody>
    914. 

  914. </table>
    915. 

  915. <pre class="literal-block">
    916. 

  916. template &lt;typename ...Args&gt;
    917. 

  917. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> operator()(Args&amp;&amp;... args) const;
    918. 

  918. </pre>
    919. 

  919. <table class="docutils field-list" frame="void" rules="none">
    920. 

  920. <col class="field-name" />
    921. 

  921. <col class="field-body" />
    922. 

  922. <tbody valign="top">
    923. 

  923. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">An <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> containing, for each <tt class="docutils literal">a</tt> ## <em>i</em>,</p>
    924. 

  924. <ul class="last">
    925. 

  925. <li><p class="first">if <tt class="docutils literal">a</tt> ## <em>i</em>  is a single-element <span class="concept">ArgumentPack</span>, its element</p>
    926. 

  926. </li>
    927. 

  927. <li><dl class="first docutils">
    928. 

  928. <dt>Otherwise, a <a class="reference internal" href="#tagged-reference">tagged reference</a> with <a class="reference internal" href="#kw">keyword</a> <tt class="docutils literal">K</tt> ## <em>i</em> and <em>value</em></dt>
    929. 

  929. <dd><p class="first last"><tt class="docutils literal">a</tt> ## <em>i</em></p>
    930. 

  930. </dd>
    931. 

  931. </dl>
    932. 

  932. </li>
    933. 

  933. </ul>
    934. 

  934. </td>
    935. 

  935. </tr>
    936. 

  936. </tbody>
    937. 

  937. </table>
    938. 

  938. </div>
    939. 

  939. <div class="section" id="optional-required">
    940. 

  940. <span id="required"></span><span id="optional"></span><h2><a class="toc-backref" href="#id44">4.4&nbsp;&nbsp;&nbsp;<tt class="docutils literal">optional</tt>, <tt class="docutils literal">required</tt></a></h2>
    941. 

  941. <p>These templates describe the requirements on a function parameter.</p>
    942. 

  942. <p><tt class="docutils literal">optional</tt> is defined in: <a class="reference external" href="../../../../boost/parameter/optional.hpp">boost/parameter/optional.hpp</a></p>
    943. 

  943. <p><tt class="docutils literal">required</tt> is defined in: <a class="reference external" href="../../../../boost/parameter/required.hpp">boost/parameter/required.hpp</a></p>
    944. 

  944. <p>Both headers are included by: <a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></p>
    945. 

  945. <table class="docutils field-list" frame="void" rules="none">
    946. 

  946. <col class="field-name" />
    947. 

  947. <col class="field-body" />
    948. 

  948. <tbody valign="top">
    949. 

  949. <tr class="field"><th class="field-name" colspan="2">Specializations model:</th></tr>
    950. 

  950. <tr class="field"><td>&nbsp;</td><td class="field-body"><a class="reference internal" href="#parameterspec"><span class="concept">ParameterSpec</span></a></td>
    951. 

  951. </tr>
    952. 

  952. </tbody>
    953. 

  953. </table>
    954. 

  954. <pre class="literal-block">
    955. 

  955. template &lt;typename Tag, typename Predicate = <em>unspecified</em>&gt;
    956. 

  956. struct optional;
    957. 

  957. 

  958. template &lt;typename Tag, typename Predicate = <em>unspecified</em>&gt;
    959. 

  959. struct required;
    960. 

  960. </pre>
    961. 

  961. <p>The default value of <tt class="docutils literal">Predicate</tt> is an unspecified <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction
    962. 

  962. Class</a> that returns <tt class="docutils literal"><span class="pre">mpl::true_</span></tt> for any argument.  If
    963. 

  963. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> is defined, then the default value of
    964. 

  964. <tt class="docutils literal">Predicate</tt> is also a <a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a>-style quoted metafunction that returns
    965. 

  965. <tt class="docutils literal"><span class="pre">mp11::mp_true</span></tt> for any argument.</p>
    966. 

  966. </div>
    967. 

  967. <div class="section" id="id9">
    968. 

  968. <span id="deduced"></span><h2><a class="toc-backref" href="#id45">4.5&nbsp;&nbsp;&nbsp;<tt class="docutils literal">deduced</tt></a></h2>
    969. 

  969. <p>This template is used to wrap the <em>keyword tag</em> argument to
    970. 

  970. <tt class="docutils literal">optional</tt> or <tt class="docutils literal">required</tt>.</p>
    971. 

  971. <table class="docutils field-list" frame="void" rules="none">
    972. 

  972. <col class="field-name" />
    973. 

  973. <col class="field-body" />
    974. 

  974. <tbody valign="top">
    975. 

  975. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/deduced.hpp">boost/parameter/deduced.hpp</a></td>
    976. 

  976. </tr>
    977. 

  977. <tr class="field"><th class="field-name">Included by:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    978. 

  978. </tr>
    979. 

  979. </tbody>
    980. 

  980. </table>
    981. 

  981. <pre class="literal-block">
    982. 

  982. template &lt;typename Tag&gt;
    983. 

  983. struct deduced;
    984. 

  984. </pre>
    985. 

  985. <table class="docutils field-list" frame="void" rules="none">
    986. 

  986. <col class="field-name" />
    987. 

  987. <col class="field-body" />
    988. 

  988. <tbody valign="top">
    989. 

  989. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">nothing</td>
    990. 

  990. </tr>
    991. 

  991. </tbody>
    992. 

  992. </table>
    993. 

  993. </div>
    994. 

  994. </div>
    995. 

  995. <hr class="docutils" />
    996. 

  996. <div class="section" id="metafunctions">
    997. 

  997. <h1><a class="toc-backref" href="#id46">5&nbsp;&nbsp;&nbsp;Metafunctions</a></h1>
    998. 

  998. <p>A <a class="reference external" href="../../../mpl/doc/refmanual/metafunction.html">Metafunction</a> is conceptually a function that operates on, and returns,
    999. 

  999. C++ types.</p>
    1000. 

  1000. <div class="section" id="id10">
    1001. 

  1001. <span id="binding"></span><h2><a class="toc-backref" href="#id47">5.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">binding</tt></a></h2>
    1002. 

  1002. <p>Returns the result type of indexing an argument pack with a
    1003. 

  1003. <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> or with a <a class="reference internal" href="#tagged-default">tagged default</a>.</p>
    1004. 

  1004. <table class="docutils field-list" frame="void" rules="none">
    1005. 

  1005. <col class="field-name" />
    1006. 

  1006. <col class="field-body" />
    1007. 

  1007. <tbody valign="top">
    1008. 

  1008. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/binding.hpp">boost/parameter/binding.hpp</a></td>
    1009. 

  1009. </tr>
    1010. 

  1010. </tbody>
    1011. 

  1011. </table>
    1012. 

  1012. <pre class="literal-block">
    1013. 

  1013. template &lt;typename A, typename K, typename D = void_&gt;
    1014. 

  1014. struct binding
    1015. 

  1015. {
    1016. 

  1016.     typedef … type;
    1017. 

  1017. };
    1018. 

  1018. </pre>
    1019. 

  1019. <table class="docutils field-list" frame="void" rules="none">
    1020. 

  1020. <col class="field-name" />
    1021. 

  1021. <col class="field-body" />
    1022. 

  1022. <tbody valign="top">
    1023. 

  1023. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal">A</tt> must be a model of <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>.</td>
    1024. 

  1024. </tr>
    1025. 

  1025. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">the reference type of the <a class="reference internal" href="#tagged-reference">tagged reference</a> in <tt class="docutils literal">A</tt> having
    1026. 

  1026. <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> <tt class="docutils literal">K</tt>, if any.  If no such <a class="reference internal" href="#tagged-reference">tagged reference</a> exists,
    1027. 

  1027. returns <tt class="docutils literal">D</tt>.</td>
    1028. 

  1028. </tr>
    1029. 

  1029. </tbody>
    1030. 

  1030. </table>
    1031. 

  1031. </div>
    1032. 

  1032. <div class="section" id="id11">
    1033. 

  1033. <span id="lazy-binding"></span><h2><a class="toc-backref" href="#id48">5.2&nbsp;&nbsp;&nbsp;<tt class="docutils literal">lazy_binding</tt></a></h2>
    1034. 

  1034. <p>Returns the result type of indexing an argument pack with a
    1035. 

  1035. <a class="reference internal" href="#tagged-lazy-default">tagged lazy default</a>.</p>
    1036. 

  1036. <table class="docutils field-list" frame="void" rules="none">
    1037. 

  1037. <col class="field-name" />
    1038. 

  1038. <col class="field-body" />
    1039. 

  1039. <tbody valign="top">
    1040. 

  1040. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/binding.hpp">boost/parameter/binding.hpp</a></td>
    1041. 

  1041. </tr>
    1042. 

  1042. </tbody>
    1043. 

  1043. </table>
    1044. 

  1044. <pre class="literal-block">
    1045. 

  1045. template &lt;typename A, typename K, typename F&gt;
    1046. 

  1046. struct lazy_binding
    1047. 

  1047. {
    1048. 

  1048.     typedef … type;
    1049. 

  1049. };
    1050. 

  1050. </pre>
    1051. 

  1051. <table class="docutils field-list" frame="void" rules="none">
    1052. 

  1052. <col class="field-name" />
    1053. 

  1053. <col class="field-body" />
    1054. 

  1054. <tbody valign="top">
    1055. 

  1055. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal">A</tt> must be a model of <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>.</td>
    1056. 

  1056. </tr>
    1057. 

  1057. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">the reference type of the <a class="reference internal" href="#tagged-reference">tagged reference</a> in <tt class="docutils literal">A</tt> having
    1058. 

  1058. <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> <tt class="docutils literal">K</tt>, if any.  If no such <a class="reference internal" href="#tagged-reference">tagged reference</a> exists,
    1059. 

  1059. returns <a class="reference external" href="../../../utility/utility.htm#result_of"><tt class="docutils literal"><span class="pre">boost::result_of</span></tt></a><tt class="docutils literal"><span class="pre">&lt;F()&gt;::type</span></tt>.<a class="footnote-reference" href="#no-result-of" id="id12"><sup>2</sup></a></td>
    1060. 

  1060. </tr>
    1061. 

  1061. </tbody>
    1062. 

  1062. </table>
    1063. 

  1063. </div>
    1064. 

  1064. <div class="section" id="id13">
    1065. 

  1065. <span id="value-type"></span><h2><a class="toc-backref" href="#id49">5.3&nbsp;&nbsp;&nbsp;<tt class="docutils literal">value_type</tt></a></h2>
    1066. 

  1066. <p>Returns the result type of indexing an argument pack with a
    1067. 

  1067. <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> or with a <a class="reference internal" href="#tagged-default">tagged default</a>.</p>
    1068. 

  1068. <table class="docutils field-list" frame="void" rules="none">
    1069. 

  1069. <col class="field-name" />
    1070. 

  1070. <col class="field-body" />
    1071. 

  1071. <tbody valign="top">
    1072. 

  1072. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/value_type.hpp">boost/parameter/value_type.hpp</a></td>
    1073. 

  1073. </tr>
    1074. 

  1074. </tbody>
    1075. 

  1075. </table>
    1076. 

  1076. <pre class="literal-block">
    1077. 

  1077. template &lt;typename A, typename K, typename D = void_&gt;
    1078. 

  1078. struct value_type
    1079. 

  1079. {
    1080. 

  1080.     typedef … type;
    1081. 

  1081. };
    1082. 

  1082. </pre>
    1083. 

  1083. <table class="docutils field-list" frame="void" rules="none">
    1084. 

  1084. <col class="field-name" />
    1085. 

  1085. <col class="field-body" />
    1086. 

  1086. <tbody valign="top">
    1087. 

  1087. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><p class="first"><tt class="docutils literal">A</tt> must be a model of <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>.</p>
    1088. 

  1088. </td>
    1089. 

  1089. </tr>
    1090. 

  1090. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">the (possibly const-qualified) type of the <a class="reference internal" href="#tagged-reference">tagged reference</a> in
    1091. 

  1091. <tt class="docutils literal">A</tt> having <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> <tt class="docutils literal">K</tt>, if any.  If no such
    1092. 

  1092. <a class="reference internal" href="#tagged-reference">tagged reference</a> exists, returns <tt class="docutils literal">D</tt>.  Equivalent to:</p>
    1093. 

  1093. <pre class="literal-block">
    1094. 

  1094. typename <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/remove_reference.html">boost::remove_reference</a>&lt;
    1095. 

  1095.     typename <a class="reference internal" href="#binding"><tt class="docutils literal">binding</tt></a>&lt;A, K, D&gt;::type
    1096. 

  1096. &gt;::type
    1097. 

  1097. </pre>
    1098. 

  1098. <p class="last">… when <tt class="docutils literal">D</tt> is not a reference type.</p>
    1099. 

  1099. </td>
    1100. 

  1100. </tr>
    1101. 

  1101. </tbody>
    1102. 

  1102. </table>
    1103. 

  1103. </div>
    1104. 

  1104. <div class="section" id="id14">
    1105. 

  1105. <span id="lazy-value-type"></span><h2><a class="toc-backref" href="#id50">5.4&nbsp;&nbsp;&nbsp;<tt class="docutils literal">lazy_value_type</tt></a></h2>
    1106. 

  1106. <p>Returns the result type of indexing an argument pack with a
    1107. 

  1107. <a class="reference internal" href="#tagged-lazy-default">tagged lazy default</a>.</p>
    1108. 

  1108. <table class="docutils field-list" frame="void" rules="none">
    1109. 

  1109. <col class="field-name" />
    1110. 

  1110. <col class="field-body" />
    1111. 

  1111. <tbody valign="top">
    1112. 

  1112. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/value_type.hpp">boost/parameter/value_type.hpp</a></td>
    1113. 

  1113. </tr>
    1114. 

  1114. </tbody>
    1115. 

  1115. </table>
    1116. 

  1116. <pre class="literal-block">
    1117. 

  1117. template &lt;typename A, typename K, typename F&gt;
    1118. 

  1118. struct lazy_value_type
    1119. 

  1119. {
    1120. 

  1120.     typedef … type;
    1121. 

  1121. };
    1122. 

  1122. </pre>
    1123. 

  1123. <table class="docutils field-list" frame="void" rules="none">
    1124. 

  1124. <col class="field-name" />
    1125. 

  1125. <col class="field-body" />
    1126. 

  1126. <tbody valign="top">
    1127. 

  1127. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal">A</tt> must be a model of <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>.</td>
    1128. 

  1128. </tr>
    1129. 

  1129. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">the (possibly const-qualified) type of the <a class="reference internal" href="#tagged-reference">tagged reference</a> in
    1130. 

  1130. <tt class="docutils literal">A</tt> having <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> <tt class="docutils literal">K</tt>, if any.  If no such
    1131. 

  1131. <a class="reference internal" href="#tagged-reference">tagged reference</a> exists, returns
    1132. 

  1132. <a class="reference external" href="../../../utility/utility.htm#result_of"><tt class="docutils literal"><span class="pre">boost::result_of</span></tt></a><tt class="docutils literal"><span class="pre">&lt;F()&gt;::type</span></tt>.<a class="footnote-reference" href="#no-result-of" id="id15"><sup>2</sup></a></td>
    1133. 

  1133. </tr>
    1134. 

  1134. </tbody>
    1135. 

  1135. </table>
    1136. 

  1136. </div>
    1137. 

  1137. <div class="section" id="id16">
    1138. 

  1138. <span id="are-tagged-arguments"></span><h2><a class="toc-backref" href="#id51">5.5&nbsp;&nbsp;&nbsp;<tt class="docutils literal">are_tagged_arguments</tt></a></h2>
    1139. 

  1139. <table class="docutils field-list" frame="void" rules="none">
    1140. 

  1140. <col class="field-name" />
    1141. 

  1141. <col class="field-body" />
    1142. 

  1142. <tbody valign="top">
    1143. 

  1143. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/are_tagged_arguments.hpp">boost/parameter/are_tagged_arguments.hpp</a></td>
    1144. 

  1144. </tr>
    1145. 

  1145. </tbody>
    1146. 

  1146. </table>
    1147. 

  1147. <pre class="literal-block">
    1148. 

  1148. template &lt;typename T0, typename ...Pack&gt;
    1149. 

  1149. struct are_tagged_arguments
    1150. 

  1150.     // : <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> if T0 and all elements in Pack are
    1151. 

  1151.     // tagged reference types, <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> otherwise.
    1152. 

  1152. {
    1153. 

  1153. };
    1154. 

  1154. </pre>
    1155. 

  1155. <table class="docutils field-list" frame="void" rules="none">
    1156. 

  1156. <col class="field-name" />
    1157. 

  1157. <col class="field-body" />
    1158. 

  1158. <tbody valign="top">
    1159. 

  1159. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">mpl::true_</span></tt> if <tt class="docutils literal">T0</tt> and all elements in parameter pack <tt class="docutils literal">Pack</tt> are
    1160. 

  1160. <a class="reference internal" href="#tagged-reference">tagged reference</a> types, <tt class="docutils literal"><span class="pre">mpl::false_</span></tt> otherwise.</td>
    1161. 

  1161. </tr>
    1162. 

  1162. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    1163. 

  1163. </tr>
    1164. 

  1164. </tbody>
    1165. 

  1165. </table>
    1166. 

  1166. <p>When implementing a Boost.Parameter-enabled constructor for a container that
    1167. 

  1167. conforms to the C++ standard, one needs to remember that the standard requires
    1168. 

  1168. the presence of other constructors that are typically defined as templates,
    1169. 

  1169. such as range constructors.  To avoid overload ambiguities between the two
    1170. 

  1170. constructors, use this metafunction in conjunction with <tt class="docutils literal">disable_if</tt> to
    1171. 

  1171. define the range constructor.</p>
    1172. 

  1172. <pre class="literal-block">
    1173. 

  1173. template &lt;typename B&gt;
    1174. 

  1174. class frontend : public B
    1175. 

  1175. {
    1176. 

  1176.     struct _enabler
    1177. 

  1177.     {
    1178. 

  1178.     };
    1179. 

  1179. 

  1180.  public:
    1181. 

  1181.     <a class="reference internal" href="#boost-parameter-no-spec-constructor"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR</tt></a>(frontend, (B))
    1182. 

  1182. 

  1183.     template &lt;typename Iterator&gt;
    1184. 

  1184.     frontend(
    1185. 

  1185.         Iterator itr
    1186. 

  1186.       , Iterator itr_end
    1187. 

  1187.       , typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>&lt;
    1188. 

  1188.             are_tagged_arguments&lt;Iterator&gt;
    1189. 

  1189.           , _enabler
    1190. 

  1190.         &gt;::type = _enabler()
    1191. 

  1191.     ) : B(itr, itr_end)
    1192. 

  1192.     {
    1193. 

  1193.     }
    1194. 

  1194. };
    1195. 

  1195. </pre>
    1196. 

  1196. </div>
    1197. 

  1197. <div class="section" id="id17">
    1198. 

  1198. <span id="is-argument-pack"></span><h2><a class="toc-backref" href="#id52">5.6&nbsp;&nbsp;&nbsp;<tt class="docutils literal">is_argument_pack</tt></a></h2>
    1199. 

  1199. <table class="docutils field-list" frame="void" rules="none">
    1200. 

  1200. <col class="field-name" />
    1201. 

  1201. <col class="field-body" />
    1202. 

  1202. <tbody valign="top">
    1203. 

  1203. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/is_argument_pack.hpp">boost/parameter/is_argument_pack.hpp</a></td>
    1204. 

  1204. </tr>
    1205. 

  1205. </tbody>
    1206. 

  1206. </table>
    1207. 

  1207. <pre class="literal-block">
    1208. 

  1208. template &lt;typename T&gt;
    1209. 

  1209. struct is_argument_pack
    1210. 

  1210.     // : <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a> if T is a model of <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>,
    1211. 

  1211.     // <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> otherwise.
    1212. 

  1212. {
    1213. 

  1213. };
    1214. 

  1214. </pre>
    1215. 

  1215. <table class="docutils field-list" frame="void" rules="none">
    1216. 

  1216. <col class="field-name" />
    1217. 

  1217. <col class="field-body" />
    1218. 

  1218. <tbody valign="top">
    1219. 

  1219. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">mpl::true_</span></tt> if <tt class="docutils literal">T</tt> is a model of <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, <tt class="docutils literal"><span class="pre">mpl::false_</span></tt>
    1220. 

  1220. otherwise.</td>
    1221. 

  1221. </tr>
    1222. 

  1222. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    1223. 

  1223. </tr>
    1224. 

  1224. </tbody>
    1225. 

  1225. </table>
    1226. 

  1226. <p>To avoid overload ambiguities between a constructor that takes in an
    1227. 

  1227. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> and a templated conversion constructor, use this
    1228. 

  1228. metafunction in conjunction with <tt class="docutils literal">enable_if</tt>.</p>
    1229. 

  1229. <pre class="literal-block">
    1230. 

  1230. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a0)
    1231. 

  1231. 

  1232. template &lt;typename T&gt;
    1233. 

  1233. class backend0
    1234. 

  1234. {
    1235. 

  1235.     struct _enabler
    1236. 

  1236.     {
    1237. 

  1237.     };
    1238. 

  1238. 

  1239.     T a0;
    1240. 

  1240. 

  1241.  public:
    1242. 

  1242.     template &lt;typename ArgPack&gt;
    1243. 

  1243.     explicit backend0(
    1244. 

  1244.         ArgPack const&amp; args
    1245. 

  1245.       , typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    1246. 

  1246.             is_argument_pack&lt;ArgPack&gt;
    1247. 

  1247.           , _enabler
    1248. 

  1248.         &gt;::type = _enabler()
    1249. 

  1249.     ) : a0(args[_a0])
    1250. 

  1250.     {
    1251. 

  1251.     }
    1252. 

  1252. 

  1253.     template &lt;typename U&gt;
    1254. 

  1254.     backend0(
    1255. 

  1255.         backend0&lt;U&gt; const&amp; copy
    1256. 

  1256.       , typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    1257. 

  1257.             <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_convertible.html">boost::is_convertible</a>&lt;U,T&gt;
    1258. 

  1258.           , _enabler
    1259. 

  1259.         &gt;::type = _enabler()
    1260. 

  1260.     ) : a0(copy.get_a0())
    1261. 

  1261.     {
    1262. 

  1262.     }
    1263. 

  1263. 

  1264.     T const&amp; get_a0() const
    1265. 

  1265.     {
    1266. 

  1266.         return this-&gt;a0;
    1267. 

  1267.     }
    1268. 

  1268. };
    1269. 

  1269. </pre>
    1270. 

  1270. </div>
    1271. 

  1271. <div class="section" id="id18">
    1272. 

  1272. <span id="result-of-compose"></span><h2><a class="toc-backref" href="#id53">5.7&nbsp;&nbsp;&nbsp;<tt class="docutils literal"><span class="pre">result_of::compose</span></tt></a></h2>
    1273. 

  1273. <p>Returns the result type of the <a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a> function.</p>
    1274. 

  1274. <table class="docutils field-list" frame="void" rules="none">
    1275. 

  1275. <col class="field-name" />
    1276. 

  1276. <col class="field-body" />
    1277. 

  1277. <tbody valign="top">
    1278. 

  1278. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/compose.hpp">boost/parameter/compose.hpp</a></td>
    1279. 

  1279. </tr>
    1280. 

  1280. </tbody>
    1281. 

  1281. </table>
    1282. 

  1282. <pre class="literal-block">
    1283. 

  1283. template &lt;typename ...TaggedArgs&gt;
    1284. 

  1284. struct compose
    1285. 

  1285.   : <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    1286. 

  1286.         <a class="reference internal" href="#are-tagged-arguments"><tt class="docutils literal">are_tagged_arguments</tt></a>&lt;T0,Pack...&gt;
    1287. 

  1287.       , <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>
    1288. 

  1288.     &gt;
    1289. 

  1289. {
    1290. 

  1290. };
    1291. 

  1291. 

  1292. template &lt;&gt;
    1293. 

  1293. struct compose&lt;&gt;
    1294. 

  1294. {
    1295. 

  1295.     typedef <em>empty</em> <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type;
    1296. 

  1296. };
    1297. 

  1297. </pre>
    1298. 

  1298. <table class="docutils field-list" frame="void" rules="none">
    1299. 

  1299. <col class="field-name" />
    1300. 

  1300. <col class="field-body" />
    1301. 

  1301. <tbody valign="top">
    1302. 

  1302. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">All elements in <tt class="docutils literal">TaggedArgs</tt> must be <a class="reference internal" href="#tagged-reference">tagged reference</a> types, if
    1303. 

  1303. specified.</td>
    1304. 

  1304. </tr>
    1305. 

  1305. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">the result type of the <a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a> function.</td>
    1306. 

  1306. </tr>
    1307. 

  1307. </tbody>
    1308. 

  1308. </table>
    1309. 

  1309. </div>
    1310. 

  1310. </div>
    1311. 

  1311. <hr class="docutils" />
    1312. 

  1312. <div class="section" id="function-templates">
    1313. 

  1313. <h1><a class="toc-backref" href="#id54">6&nbsp;&nbsp;&nbsp;Function Templates</a></h1>
    1314. 

  1314. <div class="section" id="id19">
    1315. 

  1315. <span id="compose"></span><h2><a class="toc-backref" href="#id55">6.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">compose</tt></a></h2>
    1316. 

  1316. <table class="docutils field-list" frame="void" rules="none">
    1317. 

  1317. <col class="field-name" />
    1318. 

  1318. <col class="field-body" />
    1319. 

  1319. <tbody valign="top">
    1320. 

  1320. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/compose.hpp">boost/parameter/compose.hpp</a></td>
    1321. 

  1321. </tr>
    1322. 

  1322. </tbody>
    1323. 

  1323. </table>
    1324. 

  1324. <pre class="literal-block">
    1325. 

  1325. template &lt;typename ...Pack&gt;
    1326. 

  1326. constexpr typename <a class="reference internal" href="#result-of-compose"><tt class="docutils literal"><span class="pre">result_of::compose</span></tt></a>&lt;Pack...&gt;::type
    1327. 

  1327.     compose(Pack const&amp;... args);
    1328. 

  1328. </pre>
    1329. 

  1329. <p>This function facilitates easier variadic argument composition.  It is used by
    1330. 

  1330. the <a class="reference internal" href="#boost-parameter-no-spec-function"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_FUNCTION</tt></a>,
    1331. 

  1331. <a class="reference internal" href="#boost-parameter-no-spec-member-function"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION</tt></a>,
    1332. 

  1332. <a class="reference internal" href="#boost-parameter-no-spec-const-member-function"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION</tt></a>,
    1333. 

  1333. <a class="reference internal" href="#boost-parameter-no-spec-function-call-operator"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR</tt></a>,
    1334. 

  1334. <a class="reference internal" href="#boost-parameter-no-spec-const-function-call-operator"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR</tt></a>,
    1335. 

  1335. <a class="reference internal" href="#boost-parameter-no-spec-constructor"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR</tt></a>, and
    1336. 

  1336. <a class="reference internal" href="#boost-parameter-no-spec-no-base-constructor"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR</tt></a> code generation macros.  You
    1337. 

  1337. can use it to write your own code generation macros if the ones provided by
    1338. 

  1338. this library do not suffice.</p>
    1339. 

  1339. <p>Unlike the <a class="reference internal" href="#tagged-reference">tagged reference</a> comma operator, the <tt class="docutils literal">compose()</tt> function is
    1340. 

  1340. variadic, as mentioned before.  However, the <a class="reference internal" href="#tagged-reference">tagged reference</a> comma operator
    1341. 

  1341. can be invoked indefinitely and therefore does not limit the size of the
    1342. 

  1342. resulting <span class="concept">ArgumentPack</span>, while the <tt class="docutils literal">compose()</tt> function cannot take in more
    1343. 

  1343. than <a class="reference internal" href="#boost-parameter-compose-max-arity"><tt class="docutils literal">BOOST_PARAMETER_COMPOSE_MAX_ARITY</tt></a> arguments for compilers that do not
    1344. 

  1344. support perfect forwarding.</p>
    1345. 

  1345. <table class="docutils field-list" frame="void" rules="none">
    1346. 

  1346. <col class="field-name" />
    1347. 

  1347. <col class="field-body" />
    1348. 

  1348. <tbody valign="top">
    1349. 

  1349. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">All elements in <tt class="docutils literal">args</tt> must be <a class="reference internal" href="#tagged-reference">tagged reference</a> objects, if
    1350. 

  1350. specified.</td>
    1351. 

  1351. </tr>
    1352. 

  1352. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">an <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> containing all elements in <tt class="docutils literal">args</tt>, if
    1353. 

  1353. specified; an empty <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> otherwise.</td>
    1354. 

  1354. </tr>
    1355. 

  1355. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    1356. 

  1356. </tr>
    1357. 

  1357. </tbody>
    1358. 

  1358. </table>
    1359. 

  1359. <pre class="literal-block">
    1360. 

  1360. BOOST_PARAMETER_NAME(index)
    1361. 

  1361. BOOST_PARAMETER_NAME(name)
    1362. 

  1362. 

  1363. template &lt;typename ArgumentPack&gt;
    1364. 

  1364. int print_name_and_index(ArgumentPack const&amp; args)
    1365. 

  1365. {
    1366. 

  1366.     std::cout &lt;&lt; &quot;index = &quot; &lt;&lt; args[_index];
    1367. 

  1367.     std::cout &lt;&lt; &quot;name = &quot; &lt;&lt; args[_name];
    1368. 

  1368.     std::cout &lt;&lt; &quot;; &quot; &lt;&lt; std::endl;
    1369. 

  1369.     return 0;
    1370. 

  1370. }
    1371. 

  1371. 

  1372. int y = print_name_and_index(compose(_index = 3, _name = &quot;jones&quot;));
    1373. 

  1373. </pre>
    1374. 

  1374. <p>The <a class="reference external" href="../../test/compose.cpp">compose.cpp</a> test program shows more examples using this function.</p>
    1375. 

  1375. </div>
    1376. 

  1376. </div>
    1377. 

  1377. <hr class="docutils" />
    1378. 

  1378. <div class="section" id="code-generation-macros">
    1379. 

  1379. <h1><a class="toc-backref" href="#id56">7&nbsp;&nbsp;&nbsp;Code Generation Macros</a></h1>
    1380. 

  1380. <p>Macros in this section can be used to ease the writing of code
    1381. 

  1381. using the Parameter library by eliminating repetitive boilerplate.</p>
    1382. 

  1382. <div class="section" id="boost-parameter-function-result-name-tag-namespace-arguments">
    1383. 

  1383. <span id="boost-parameter-function"></span><h2><a class="toc-backref" href="#id57">7.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_FUNCTION(result, name, tag_namespace, arguments)</tt></a></h2>
    1384. 

  1384. <table class="docutils field-list" frame="void" rules="none">
    1385. 

  1385. <col class="field-name" />
    1386. 

  1386. <col class="field-body" />
    1387. 

  1387. <tbody valign="top">
    1388. 

  1388. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    1389. 

  1389. </tr>
    1390. 

  1390. </tbody>
    1391. 

  1391. </table>
    1392. 

  1392. <p>Generates a function that can take in positional arguments, composed
    1393. 

  1393. arguments, named arguments, and deduced arguments.</p>
    1394. 

  1394. <table class="docutils field-list" frame="void" rules="none">
    1395. 

  1395. <col class="field-name" />
    1396. 

  1396. <col class="field-body" />
    1397. 

  1397. <tbody valign="top">
    1398. 

  1398. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    1399. 

  1399. </tr>
    1400. 

  1400. </tbody>
    1401. 

  1401. </table>
    1402. 

  1402. <p>The return type of each of the following function templates falls under a
    1403. 

  1403. different value category.</p>
    1404. 

  1404. <pre class="literal-block">
    1405. 

  1405. template &lt;std::size_t N&gt;
    1406. 

  1406. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    1407. 

  1407. {
    1408. 

  1408.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    1409. 

  1409. }
    1410. 

  1410. 

  1411. template &lt;std::size_t N&gt;
    1412. 

  1412. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    1413. 

  1413. {
    1414. 

  1414.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    1415. 

  1415. }
    1416. 

  1416. 

  1417. template &lt;std::size_t N&gt;
    1418. 

  1418. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    1419. 

  1419. {
    1420. 

  1420.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    1421. 

  1421.     return lset;
    1422. 

  1422. }
    1423. 

  1423. 

  1424. template &lt;std::size_t N&gt;
    1425. 

  1425. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    1426. 

  1426. {
    1427. 

  1427.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    1428. 

  1428.     return clset;
    1429. 

  1429. }
    1430. 

  1430. </pre>
    1431. 

  1431. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    1432. 

  1432. to return the correct value category when passed in an object returned by one
    1433. 

  1433. of the functions defined above.  Assume that
    1434. 

  1434. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    1435. 

  1435. <pre class="literal-block">
    1436. 

  1436. enum invoked
    1437. 

  1437. {
    1438. 

  1438.     passed_by_lvalue_reference_to_const
    1439. 

  1439.   , passed_by_lvalue_reference
    1440. 

  1440.   , passed_by_rvalue_reference_to_const
    1441. 

  1441.   , passed_by_rvalue_reference
    1442. 

  1442. };
    1443. 

  1443. 

  1444. struct U
    1445. 

  1445. {
    1446. 

  1446.     template &lt;std::size_t N&gt;
    1447. 

  1447.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    1448. 

  1448.     {
    1449. 

  1449.         return passed_by_lvalue_reference_to_const;
    1450. 

  1450.     }
    1451. 

  1451. 

  1452.     template &lt;std::size_t N&gt;
    1453. 

  1453.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    1454. 

  1454.     {
    1455. 

  1455.         return passed_by_lvalue_reference;
    1456. 

  1456.     }
    1457. 

  1457. 

  1458.     template &lt;std::size_t N&gt;
    1459. 

  1459.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    1460. 

  1460.     {
    1461. 

  1461.         return passed_by_rvalue_reference_to_const;
    1462. 

  1462.     }
    1463. 

  1463. 

  1464.     template &lt;std::size_t N&gt;
    1465. 

  1465.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    1466. 

  1466.     {
    1467. 

  1467.         return passed_by_rvalue_reference;
    1468. 

  1468.     }
    1469. 

  1469. };
    1470. 

  1470. </pre>
    1471. 

  1471. <p>Define the named parameters that will comprise the argument specification that
    1472. 

  1472. this macro will use.  Ensure that all their tag types are in the same
    1473. 

  1473. namespace, which is <tt class="docutils literal">kw</tt> in this case.  The identifiers with leading
    1474. 

  1474. underscores can be passed to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    1475. 

  1475. same argument to which the corresponding named parameter (without underscores)
    1476. 

  1476. is bound, as will be shown later.</p>
    1477. 

  1477. <pre class="literal-block">
    1478. 

  1478. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw) in(lrc))
    1479. 

  1479. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw) in_out(lr))
    1480. 

  1480. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw) in(rrc))
    1481. 

  1481. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw) consume(rr))
    1482. 

  1482. </pre>
    1483. 

  1483. <p>Use the macro as a substitute for a normal function header.  Enclose the
    1484. 

  1484. return type <tt class="docutils literal">bool</tt> in parentheses.  For each parameter, also enclose the
    1485. 

  1485. expected value type in parentheses.  Since the value types are mutually
    1486. 

  1486. exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    1487. 

  1487. clause.  Otherwise, just as with a normal function, the order in which you
    1488. 

  1488. specify the parameters determines their position.  Also, just as with a normal
    1489. 

  1489. function, optional parameters have default values, whereas required parameters
    1490. 

  1490. do not.  Within the function body, either simply use the parameter name or
    1491. 

  1491. pass the matching identifier with the leading underscore to the bracket
    1492. 

  1492. operator of <tt class="docutils literal">args</tt> to extract the corresponding argument.  Note that the
    1493. 

  1493. second method doesn't require <tt class="docutils literal"><span class="pre">std::forward</span></tt> to preserve value categories.</p>
    1494. 

  1494. <pre class="literal-block">
    1495. 

  1495. BOOST_PARAMETER_FUNCTION((bool), evaluate, kw,
    1496. 

  1496.     (deduced
    1497. 

  1497.         (required
    1498. 

  1498.             (lrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;1&gt;))
    1499. 

  1499.             (lr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;2&gt;))
    1500. 

  1500.         )
    1501. 

  1501.         (optional
    1502. 

  1502.             (rrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;3&gt;), rvalue_const_bitset&lt;2&gt;())
    1503. 

  1503.             (rr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;4&gt;), rvalue_bitset&lt;3&gt;())
    1504. 

  1504.         )
    1505. 

  1505.     )
    1506. 

  1506. )
    1507. 

  1507. {
    1508. 

  1508.     BOOST_TEST_EQ(
    1509. 

  1509.         passed_by_lvalue_reference_to_const
    1510. 

  1510.       , U::evaluate_category&lt;0&gt;(lrc)
    1511. 

  1511.     );
    1512. 

  1512.     BOOST_TEST_EQ(
    1513. 

  1513.         passed_by_lvalue_reference
    1514. 

  1514.       , U::evaluate_category&lt;1&gt;(lr)
    1515. 

  1515.     );
    1516. 

  1516.     BOOST_TEST_EQ(
    1517. 

  1517.         passed_by_rvalue_reference_to_const
    1518. 

  1518.       , U::evaluate_category&lt;2&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;rrc0_type&gt;(rrc0))
    1519. 

  1519.     );
    1520. 

  1520.     BOOST_TEST_EQ(
    1521. 

  1521.         passed_by_rvalue_reference
    1522. 

  1522.       , U::evaluate_category&lt;3&gt;(args[_rr0])
    1523. 

  1523.     );
    1524. 

  1524. 

  1525.     return true;
    1526. 

  1526. }
    1527. 

  1527. </pre>
    1528. 

  1528. <p>The following function calls are legal.</p>
    1529. 

  1529. <pre class="literal-block">
    1530. 

  1530. evaluate(  // positional arguments
    1531. 

  1531.     lvalue_const_bitset&lt;0&gt;()
    1532. 

  1532.   , lvalue_bitset&lt;1&gt;()
    1533. 

  1533.   , rvalue_const_bitset&lt;2&gt;()
    1534. 

  1534.   , rvalue_bitset&lt;3&gt;()
    1535. 

  1535. );
    1536. 

  1536. evaluate(  // positional arguments
    1537. 

  1537.     lvalue_const_bitset&lt;0&gt;()
    1538. 

  1538.   , lvalue_bitset&lt;1&gt;()
    1539. 

  1539. );
    1540. 

  1540. evaluate((  // composed arguments
    1541. 

  1541.     _rr0 = rvalue_bitset&lt;3&gt;()
    1542. 

  1542.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    1543. 

  1543.   , _lr0 = lvalue_bitset&lt;1&gt;()
    1544. 

  1544.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    1545. 

  1545. ));
    1546. 

  1546. evaluate(  // named arguments
    1547. 

  1547.     _rr0 = rvalue_bitset&lt;3&gt;()
    1548. 

  1548.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    1549. 

  1549.   , _lr0 = lvalue_bitset&lt;1&gt;()
    1550. 

  1550.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    1551. 

  1551. );
    1552. 

  1552. evaluate(  // named arguments
    1553. 

  1553.     _lr0 = lvalue_bitset&lt;1&gt;()
    1554. 

  1554.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    1555. 

  1555. );
    1556. 

  1556. </pre>
    1557. 

  1557. <p>Because the parameters were wrapped in a <tt class="docutils literal">(deduced …)</tt> clause, the following
    1558. 

  1558. function calls are also legal.</p>
    1559. 

  1559. <pre class="literal-block">
    1560. 

  1560. evaluate(  // deduced arguments
    1561. 

  1561.     rvalue_bitset&lt;3&gt;()
    1562. 

  1562.   , lvalue_const_bitset&lt;0&gt;()
    1563. 

  1563.   , lvalue_bitset&lt;1&gt;()
    1564. 

  1564.   , rvalue_const_bitset&lt;2&gt;()
    1565. 

  1565. );
    1566. 

  1566. evaluate(  // deduced arguments
    1567. 

  1567.     lvalue_bitset&lt;1&gt;()
    1568. 

  1568.   , lvalue_const_bitset&lt;0&gt;()
    1569. 

  1569. );
    1570. 

  1570. </pre>
    1571. 

  1571. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a>, <a class="reference external" href="../../test/preprocessor_deduced.cpp">preprocessor_deduced.cpp</a>, and
    1572. 

  1572. <a class="reference external" href="../../test/preprocessor_eval_category.cpp">preprocessor_eval_category.cpp</a> test programs demonstrate proper usage of this
    1573. 

  1573. macro.</p>
    1574. 

  1574. <p><strong>Macro parameters:</strong></p>
    1575. 

  1575. <ul class="simple">
    1576. 

  1576. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    1577. 

  1577. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    1578. 

  1578. generated forwarding functions.</li>
    1579. 

  1579. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    1580. 

  1580. function resides.</li>
    1581. 

  1581. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    1582. 

  1582. <em>argument-specifiers</em>, as defined below.</li>
    1583. 

  1583. </ul>
    1584. 

  1584. <p><strong>Argument specifiers syntax:</strong></p>
    1585. 

  1585. <pre class="literal-block">
    1586. 

  1586. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    1587. 

  1587. 

  1588. specifier-group0 ::= <em>specifier-group1</em> |
    1589. 

  1589.     (
    1590. 

  1590.         '<strong>(</strong>' '<strong>deduced</strong>'
    1591. 

  1591.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    1592. 

  1592.         '<strong>)</strong>'
    1593. 

  1593.     )
    1594. 

  1594. 

  1595. specifier-group1 ::=
    1596. 

  1596.     (
    1597. 

  1597.         '<strong>(</strong>' '<strong>optional</strong>'
    1598. 

  1598.             <em>optional-specifier</em> {<em>optional-specifier</em>}
    1599. 

  1599.         '<strong>)</strong>'
    1600. 

  1600.     ) | (
    1601. 

  1601.         '<strong>(</strong>' '<strong>required</strong>'
    1602. 

  1602.             <em>required-specifier</em> {<em>required-specifier</em>}
    1603. 

  1603.         '<strong>)</strong>'
    1604. 

  1604.     )
    1605. 

  1605. 

  1606. optional-specifier ::=
    1607. 

  1607.     '<strong>(</strong>'
    1608. 

  1608.         <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> '<strong>,</strong>' <em>default-value</em>
    1609. 

  1609.     ')'
    1610. 

  1610. 

  1611. required-specifier ::=
    1612. 

  1612.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    1613. 

  1613. 

  1614. restriction ::=
    1615. 

  1615.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    1616. 

  1616.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    1617. 

  1617.     '<strong>*</strong>'
    1618. 

  1618. </pre>
    1619. 

  1619. <ul class="simple">
    1620. 

  1620. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    1621. 

  1621. <li><tt class="docutils literal"><span class="pre">default-value</span></tt> is any valid C++ expression; if necessary, user code can
    1622. 

  1622. compute it in terms of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>, where <tt class="docutils literal"><span class="pre">previous-name</span></tt>
    1623. 

  1623. is the <tt class="docutils literal"><span class="pre">argument-name</span></tt> in a previous <tt class="docutils literal"><span class="pre">specifier-group0</span></tt> or
    1624. 

  1624. <tt class="docutils literal"><span class="pre">specifier-group1</span></tt>.  <em>This expression will be invoked exactly once.</em></li>
    1625. 

  1625. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    1626. 

  1626. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    1627. 

  1627. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    1628. 

  1628. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    1629. 

  1629. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    1630. 

  1630. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    1631. 

  1631. Metafunction Class</a> whose first argument will be the type of the
    1632. 

  1632. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    1633. 

  1633. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.  If
    1634. 

  1634. <tt class="docutils literal">restriction</tt> uses this form, then the type of the generated name
    1635. 

  1635. <tt class="docutils literal"><span class="pre">argument-name</span> ## _type</tt> will be computed in terms of the <strong>target
    1636. 

  1636. type</strong>, and the generated reference <tt class="docutils literal"><span class="pre">argument-name</span></tt> (but not its
    1637. 

  1637. corresponding entry in <tt class="docutils literal">args</tt>) will be cast to that type.</li>
    1638. 

  1638. </ul>
    1639. 

  1639. <p><strong>Approximate expansion:</strong></p>
    1640. 

  1640. <p>Where:</p>
    1641. 

  1641. <ul class="simple">
    1642. 

  1642. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    1643. 

  1643. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    1644. 

  1644. </ul>
    1645. 

  1645. <pre class="literal-block">
    1646. 

  1646. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    1647. 

  1647. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    1648. 

  1648. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    1649. 

  1649. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    1650. 

  1650. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    1651. 

  1651. template &lt;typename Args&gt;
    1652. 

  1652. using boost_param_result_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    1653. 

  1653. 

  1654. // If <strong>result</strong> is a simple return type:
    1655. 

  1655. template &lt;typename Args&gt;
    1656. 

  1656. struct boost_param_result_ ## __LINE__ ## <strong>name</strong>
    1657. 

  1657. {
    1658. 

  1658.     typedef <strong>result</strong> type;
    1659. 

  1659. };
    1660. 

  1660. 

  1661. struct boost_param_params_ ## __LINE__ ## <strong>name</strong>
    1662. 

  1662.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    1663. 

  1663.         <em>list of parameter specifications, based on arguments</em>
    1664. 

  1664.     &gt;
    1665. 

  1665. {
    1666. 

  1666. };
    1667. 

  1667. 

  1668. typedef boost_param_params_ ## __LINE__ ## <strong>name</strong>
    1669. 

  1669.     boost_param_parameters_ ## __LINE__ ## <strong>name</strong>;
    1670. 

  1670. 

  1671. template &lt;typename Args&gt;
    1672. 

  1672. typename boost_param_result_ ## __LINE__ ## <strong>name</strong>&lt;Args&gt;::type
    1673. 

  1673.     boost_param_impl ## __LINE__ ## <strong>name</strong>(Args const&amp;);
    1674. 

  1674. 

  1675. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    1676. 

  1676. <strong>result</strong> <strong>name</strong>(
    1677. 

  1677.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    1678. 

  1678.   , typename boost_param_parameters_ ## __LINE__ ## <strong>name</strong>
    1679. 

  1679.     ::match&lt;A0, …, A ## <strong>n</strong>&gt;::type
    1680. 

  1680.     = boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()
    1681. 

  1681. )
    1682. 

  1682. {
    1683. 

  1683.     return boost_param_impl ## __LINE__ ## <strong>name</strong>(
    1684. 

  1684.         boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()(
    1685. 

  1685.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    1686. 

  1686.           , …
    1687. 

  1687.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    1688. 

  1688.         )
    1689. 

  1689.     );
    1690. 

  1690. }
    1691. 

  1691. 

  1692. <span class="vellipsis">⋮</span>
    1693. 

  1693. 

  1694. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    1695. 

  1695. <strong>result</strong> <strong>name</strong>(
    1696. 

  1696.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    1697. 

  1697.   , typename boost_param_parameters_ ## __LINE__ ## <strong>name</strong>
    1698. 

  1698.     ::match&lt;A0, …, A ## <strong>m</strong>&gt;::type
    1699. 

  1699.     = boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()
    1700. 

  1700. )
    1701. 

  1701. {
    1702. 

  1702.     return boost_param_impl ## __LINE__ ## <strong>name</strong>(
    1703. 

  1703.         boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()(
    1704. 

  1704.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    1705. 

  1705.           , …
    1706. 

  1706.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    1707. 

  1707.         )
    1708. 

  1708.     );
    1709. 

  1709. }
    1710. 

  1710. 

  1711. template &lt;
    1712. 

  1712.     typename ResultType
    1713. 

  1713.   , typename Args
    1714. 

  1714.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    1715. 

  1715.   , …
    1716. 

  1716.   , typename <em>argument name</em> ## <strong>n</strong> ## _type
    1717. 

  1717. &gt;
    1718. 

  1718. ResultType
    1719. 

  1719.     boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    1720. 

  1720.         (ResultType(*)())
    1721. 

  1721.       , Args const&amp; args
    1722. 

  1722.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    1723. 

  1723.       , …
    1724. 

  1724.       , <em>argument name</em> ## <strong>n</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>m</strong>
    1725. 

  1725.     );
    1726. 

  1726. 

  1727. <span class="vellipsis">⋮</span>
    1728. 

  1728. 

  1729. template &lt;
    1730. 

  1730.     typename ResultType
    1731. 

  1731.   , typename Args
    1732. 

  1732.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    1733. 

  1733.   , …
    1734. 

  1734.   , typename <em>argument name</em> ## <strong>m</strong> ## _type
    1735. 

  1735. &gt;
    1736. 

  1736. ResultType
    1737. 

  1737.     boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    1738. 

  1738.         (ResultType(*)())
    1739. 

  1739.       , Args const&amp; args
    1740. 

  1740.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    1741. 

  1741.       , …
    1742. 

  1742.       , <em>argument name</em> ## <strong>m</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>m</strong>
    1743. 

  1743.     );
    1744. 

  1744. 

  1745. template &lt;typename Args&gt;
    1746. 

  1746. typename boost_param_result_ ## __LINE__ ## <strong>name</strong>&lt;Args&gt;::type
    1747. 

  1747.     boost_param_impl ## __LINE__ ## <strong>name</strong>(Args const&amp; args)
    1748. 

  1748. {
    1749. 

  1749.     return boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    1750. 

  1750.         static_cast&lt;
    1751. 

  1751.             typename boost_param_result_ ## __LINE__ ## <strong>name</strong>&lt;
    1752. 

  1752.                 Args
    1753. 

  1753.             &gt;::type(*)()
    1754. 

  1754.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    1755. 

  1755.       , args
    1756. 

  1756.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    1757. 

  1757.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    1758. 

  1758.                 Args
    1759. 

  1759.               , <em>keyword tag type of required parameter</em> ## <strong>0</strong>
    1760. 

  1760.             &gt;::type
    1761. 

  1761.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>0</strong>])
    1762. 

  1762.       , …
    1763. 

  1763.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    1764. 

  1764.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    1765. 

  1765.                 Args
    1766. 

  1766.               , <em>keyword tag type of required parameter</em> ## <strong>n</strong>
    1767. 

  1767.             &gt;::type
    1768. 

  1768.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>n</strong>])
    1769. 

  1769.     );
    1770. 

  1770. }
    1771. 

  1771. 

  1772. template &lt;
    1773. 

  1773.     typename ResultType
    1774. 

  1774.   , typename Args
    1775. 

  1775.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    1776. 

  1776.   , …
    1777. 

  1777.   , typename <em>argument name</em> ## <strong>n</strong> ## _type
    1778. 

  1778. &gt;
    1779. 

  1779. ResultType
    1780. 

  1780.     boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    1781. 

  1781.         (ResultType(*)())
    1782. 

  1782.       , Args const&amp; args
    1783. 

  1783.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    1784. 

  1784.       , …
    1785. 

  1785.       , <em>argument name</em> ## <strong>n</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>n</strong>
    1786. 

  1786.     )
    1787. 

  1787. {
    1788. 

  1788.     return boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    1789. 

  1789.         static_cast&lt;ResultType(*)()&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    1790. 

  1790.       , (args, <em>keyword object of optional parameter</em> ## <strong>n + 1</strong> =
    1791. 

  1791.             <em>default value of optional parameter</em> ## <strong>n + 1</strong>
    1792. 

  1792.         )
    1793. 

  1793.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>0</strong> ## _type&gt;(
    1794. 

  1794.             <em>argument name</em> ## <strong>0</strong>
    1795. 

  1795.         )
    1796. 

  1796.       , …
    1797. 

  1797.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>n</strong> ## _type&gt;(
    1798. 

  1798.             <em>argument name</em> ## <strong>n</strong>
    1799. 

  1799.         )
    1800. 

  1800.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    1801. 

  1801.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    1802. 

  1802.                 Args
    1803. 

  1803.               , <em>keyword tag type of optional parameter</em> ## <strong>n + 1</strong>
    1804. 

  1804.             &gt;::type
    1805. 

  1805.         &gt;(<em>default value of optional parameter</em> ## <strong>n + 1</strong>)
    1806. 

  1806.     );
    1807. 

  1807. }
    1808. 

  1808. 

  1809. <span class="vellipsis">⋮</span>
    1810. 

  1810. 

  1811. template &lt;
    1812. 

  1812.     typename ResultType
    1813. 

  1813.   , typename Args
    1814. 

  1814.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    1815. 

  1815.   , …
    1816. 

  1816.   , typename <em>argument name</em> ## <strong>m</strong> ## _type
    1817. 

  1817. &gt;
    1818. 

  1818. ResultType
    1819. 

  1819.     boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    1820. 

  1820.         (ResultType(*)())
    1821. 

  1821.       , Args const&amp; args
    1822. 

  1822.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    1823. 

  1823.       , …
    1824. 

  1824.       , <em>argument name</em> ## <strong>m</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>m</strong>
    1825. 

  1825.     )
    1826. 

  1826. </pre>
    1827. 

  1827. </div>
    1828. 

  1828. <div class="section" id="boost-parameter-member-function-result-name-tag-namespace-arguments">
    1829. 

  1829. <span id="boost-parameter-member-function"></span><h2><a class="toc-backref" href="#id58">7.2&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_MEMBER_FUNCTION(result, name, tag_namespace, arguments)</tt></a></h2>
    1830. 

  1830. <table class="docutils field-list" frame="void" rules="none">
    1831. 

  1831. <col class="field-name" />
    1832. 

  1832. <col class="field-body" />
    1833. 

  1833. <tbody valign="top">
    1834. 

  1834. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    1835. 

  1835. </tr>
    1836. 

  1836. </tbody>
    1837. 

  1837. </table>
    1838. 

  1838. <p>Generates a member function that can take in positional arguments, composed
    1839. 

  1839. arguments, named arguments, and deduced arguments.</p>
    1840. 

  1840. <table class="docutils field-list" frame="void" rules="none">
    1841. 

  1841. <col class="field-name" />
    1842. 

  1842. <col class="field-body" />
    1843. 

  1843. <tbody valign="top">
    1844. 

  1844. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    1845. 

  1845. </tr>
    1846. 

  1846. </tbody>
    1847. 

  1847. </table>
    1848. 

  1848. <p>The return type of each of the following function templates falls under a
    1849. 

  1849. different value category.</p>
    1850. 

  1850. <pre class="literal-block">
    1851. 

  1851. template &lt;std::size_t N&gt;
    1852. 

  1852. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    1853. 

  1853. {
    1854. 

  1854.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    1855. 

  1855. }
    1856. 

  1856. 

  1857. template &lt;std::size_t N&gt;
    1858. 

  1858. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    1859. 

  1859. {
    1860. 

  1860.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    1861. 

  1861. }
    1862. 

  1862. 

  1863. template &lt;std::size_t N&gt;
    1864. 

  1864. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    1865. 

  1865. {
    1866. 

  1866.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    1867. 

  1867.     return lset;
    1868. 

  1868. }
    1869. 

  1869. 

  1870. template &lt;std::size_t N&gt;
    1871. 

  1871. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    1872. 

  1872. {
    1873. 

  1873.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    1874. 

  1874.     return clset;
    1875. 

  1875. }
    1876. 

  1876. </pre>
    1877. 

  1877. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    1878. 

  1878. to return the correct value category when passed in an object returned by one
    1879. 

  1879. of the functions defined above.  Assume that
    1880. 

  1880. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    1881. 

  1881. <pre class="literal-block">
    1882. 

  1882. enum invoked
    1883. 

  1883. {
    1884. 

  1884.     passed_by_lvalue_reference_to_const
    1885. 

  1885.   , passed_by_lvalue_reference
    1886. 

  1886.   , passed_by_rvalue_reference_to_const
    1887. 

  1887.   , passed_by_rvalue_reference
    1888. 

  1888. };
    1889. 

  1889. 

  1890. struct U
    1891. 

  1891. {
    1892. 

  1892.     template &lt;std::size_t N&gt;
    1893. 

  1893.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    1894. 

  1894.     {
    1895. 

  1895.         return passed_by_lvalue_reference_to_const;
    1896. 

  1896.     }
    1897. 

  1897. 

  1898.     template &lt;std::size_t N&gt;
    1899. 

  1899.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    1900. 

  1900.     {
    1901. 

  1901.         return passed_by_lvalue_reference;
    1902. 

  1902.     }
    1903. 

  1903. 

  1904.     template &lt;std::size_t N&gt;
    1905. 

  1905.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    1906. 

  1906.     {
    1907. 

  1907.         return passed_by_rvalue_reference_to_const;
    1908. 

  1908.     }
    1909. 

  1909. 

  1910.     template &lt;std::size_t N&gt;
    1911. 

  1911.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    1912. 

  1912.     {
    1913. 

  1913.         return passed_by_rvalue_reference;
    1914. 

  1914.     }
    1915. 

  1915. };
    1916. 

  1916. </pre>
    1917. 

  1917. <p>Define the named parameters that will comprise the argument specification that
    1918. 

  1918. this macro will use.  Ensure that all their tag types are in the same
    1919. 

  1919. namespace, which is <tt class="docutils literal">kw</tt> in this case.  The identifiers with leading
    1920. 

  1920. underscores can be passed to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    1921. 

  1921. same argument to which the corresponding named parameter (without underscores)
    1922. 

  1922. is bound, as will be shown later.</p>
    1923. 

  1923. <pre class="literal-block">
    1924. 

  1924. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw) in(lrc))
    1925. 

  1925. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw) in_out(lr))
    1926. 

  1926. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw) in(rrc))
    1927. 

  1927. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw) consume(rr))
    1928. 

  1928. </pre>
    1929. 

  1929. <p>Use the macro as a substitute for a normal <tt class="docutils literal">static</tt> member function
    1930. 

  1930. header.  Enclose the return type <tt class="docutils literal">bool</tt> in parentheses.  For each parameter,
    1931. 

  1931. also enclose the expected value type in parentheses.  Since the value types
    1932. 

  1932. are mutually exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    1933. 

  1933. clause.  Otherwise, just as with a normal function, the order in which you
    1934. 

  1934. specify the parameters determines their position.  Also, just as with a normal
    1935. 

  1935. function, optional parameters have default values, whereas required parameters
    1936. 

  1936. do not.  Within the function body, either simply use the parameter name or
    1937. 

  1937. pass the matching identifier with the leading underscore to the bracket
    1938. 

  1938. operator of <tt class="docutils literal">args</tt> to extract the corresponding argument.  Note that the
    1939. 

  1939. second method doesn't require <tt class="docutils literal"><span class="pre">std::forward</span></tt> to preserve value categories.</p>
    1940. 

  1940. <pre class="literal-block">
    1941. 

  1941. struct B
    1942. 

  1942. {
    1943. 

  1943.     BOOST_PARAMETER_MEMBER_FUNCTION((bool), static evaluate, kw,
    1944. 

  1944.         (deduced
    1945. 

  1945.             (required
    1946. 

  1946.                 (lrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;1&gt;))
    1947. 

  1947.                 (lr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;2&gt;))
    1948. 

  1948.             )
    1949. 

  1949.             (optional
    1950. 

  1950.                 (rrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;3&gt;), rvalue_const_bitset&lt;2&gt;())
    1951. 

  1951.                 (rr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;4&gt;), rvalue_bitset&lt;3&gt;())
    1952. 

  1952.             )
    1953. 

  1953.         )
    1954. 

  1954.     )
    1955. 

  1955.     {
    1956. 

  1956.         BOOST_TEST_EQ(
    1957. 

  1957.             passed_by_lvalue_reference_to_const
    1958. 

  1958.           , U::evaluate_category&lt;0&gt;(lrc)
    1959. 

  1959.         );
    1960. 

  1960.         BOOST_TEST_EQ(
    1961. 

  1961.             passed_by_lvalue_reference
    1962. 

  1962.           , U::evaluate_category&lt;1&gt;(lr)
    1963. 

  1963.         );
    1964. 

  1964.         BOOST_TEST_EQ(
    1965. 

  1965.             passed_by_rvalue_reference_to_const
    1966. 

  1966.           , U::evaluate_category&lt;2&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;rrc0_type&gt;(rrc0))
    1967. 

  1967.         );
    1968. 

  1968.         BOOST_TEST_EQ(
    1969. 

  1969.             passed_by_rvalue_reference
    1970. 

  1970.           , U::evaluate_category&lt;3&gt;(args[_rr0])
    1971. 

  1971.         );
    1972. 

  1972. 

  1973.         return true;
    1974. 

  1974.     }
    1975. 

  1975. };
    1976. 

  1976. </pre>
    1977. 

  1977. <p>The following function calls are legal.</p>
    1978. 

  1978. <pre class="literal-block">
    1979. 

  1979. B::evaluate(  // positional arguments
    1980. 

  1980.     lvalue_const_bitset&lt;0&gt;()
    1981. 

  1981.   , lvalue_bitset&lt;1&gt;()
    1982. 

  1982.   , rvalue_const_bitset&lt;2&gt;()
    1983. 

  1983.   , rvalue_bitset&lt;3&gt;()
    1984. 

  1984. );
    1985. 

  1985. B::evaluate(  // positional arguments
    1986. 

  1986.     lvalue_const_bitset&lt;0&gt;()
    1987. 

  1987.   , lvalue_bitset&lt;1&gt;()
    1988. 

  1988. );
    1989. 

  1989. B::evaluate((  // composed arguments
    1990. 

  1990.     _rr0 = rvalue_bitset&lt;3&gt;()
    1991. 

  1991.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    1992. 

  1992.   , _lr0 = lvalue_bitset&lt;1&gt;()
    1993. 

  1993.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    1994. 

  1994. ));
    1995. 

  1995. B::evaluate(  // named arguments
    1996. 

  1996.     _rr0 = rvalue_bitset&lt;3&gt;()
    1997. 

  1997.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    1998. 

  1998.   , _lr0 = lvalue_bitset&lt;1&gt;()
    1999. 

  1999.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    2000. 

  2000. );
    2001. 

  2001. B::evaluate(  // named arguments
    2002. 

  2002.     _lr0 = lvalue_bitset&lt;1&gt;()
    2003. 

  2003.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    2004. 

  2004. );
    2005. 

  2005. </pre>
    2006. 

  2006. <p>Because the parameters were wrapped in a <tt class="docutils literal">(deduced …)</tt> clause, the following
    2007. 

  2007. function calls are also legal.</p>
    2008. 

  2008. <pre class="literal-block">
    2009. 

  2009. B::evaluate(  // deduced arguments
    2010. 

  2010.     rvalue_bitset&lt;3&gt;()
    2011. 

  2011.   , lvalue_const_bitset&lt;0&gt;()
    2012. 

  2012.   , lvalue_bitset&lt;1&gt;()
    2013. 

  2013.   , rvalue_const_bitset&lt;2&gt;()
    2014. 

  2014. );
    2015. 

  2015. B::evaluate(  // deduced arguments
    2016. 

  2016.     lvalue_bitset&lt;1&gt;()
    2017. 

  2017.   , lvalue_const_bitset&lt;0&gt;()
    2018. 

  2018. );
    2019. 

  2019. </pre>
    2020. 

  2020. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> and <a class="reference external" href="../../test/preprocessor_eval_category.cpp">preprocessor_eval_category.cpp</a> test programs
    2021. 

  2021. demonstrate proper usage of this macro.</p>
    2022. 

  2022. <p><strong>Macro parameters:</strong></p>
    2023. 

  2023. <ul class="simple">
    2024. 

  2024. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    2025. 

  2025. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    2026. 

  2026. generated forwarding functions.  <tt class="docutils literal">name</tt> may be qualified by the
    2027. 

  2027. <tt class="docutils literal">static</tt> keyword to declare the member function and its helpers as not
    2028. 

  2028. associated with any object of the enclosing type.</li>
    2029. 

  2029. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    2030. 

  2030. function resides.</li>
    2031. 

  2031. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    2032. 

  2032. <em>argument-specifiers</em>, as defined below.</li>
    2033. 

  2033. </ul>
    2034. 

  2034. <p><strong>Argument specifiers syntax:</strong></p>
    2035. 

  2035. <pre class="literal-block">
    2036. 

  2036. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    2037. 

  2037. 

  2038. specifier-group0 ::= <em>specifier-group1</em> |
    2039. 

  2039.     (
    2040. 

  2040.         '<strong>(</strong>' '<strong>deduced</strong>'
    2041. 

  2041.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    2042. 

  2042.         '<strong>)</strong>'
    2043. 

  2043.     )
    2044. 

  2044. 

  2045. specifier-group1 ::=
    2046. 

  2046.     (
    2047. 

  2047.         '<strong>(</strong>' '<strong>optional</strong>'
    2048. 

  2048.             <em>optional-specifier</em> {<em>optional-specifier</em>}
    2049. 

  2049.         '<strong>)</strong>'
    2050. 

  2050.     ) | (
    2051. 

  2051.         '<strong>(</strong>' '<strong>required</strong>'
    2052. 

  2052.             <em>required-specifier</em> {<em>required-specifier</em>}
    2053. 

  2053.         '<strong>)</strong>'
    2054. 

  2054.     )
    2055. 

  2055. 

  2056. optional-specifier ::=
    2057. 

  2057.     '<strong>(</strong>'
    2058. 

  2058.         <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> '<strong>,</strong>' <em>default-value</em>
    2059. 

  2059.     ')'
    2060. 

  2060. 

  2061. required-specifier ::=
    2062. 

  2062.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    2063. 

  2063. 

  2064. restriction ::=
    2065. 

  2065.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    2066. 

  2066.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    2067. 

  2067.     '<strong>*</strong>'
    2068. 

  2068. </pre>
    2069. 

  2069. <ul class="simple">
    2070. 

  2070. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    2071. 

  2071. <li><tt class="docutils literal"><span class="pre">default-value</span></tt> is any valid C++ expression; if necessary, user code can
    2072. 

  2072. compute it in terms of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>, where <tt class="docutils literal"><span class="pre">previous-name</span></tt>
    2073. 

  2073. is the <tt class="docutils literal"><span class="pre">argument-name</span></tt> in a previous <tt class="docutils literal"><span class="pre">specifier-group0</span></tt> or
    2074. 

  2074. <tt class="docutils literal"><span class="pre">specifier-group1</span></tt>.  <em>This expression will be invoked exactly once.</em></li>
    2075. 

  2075. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    2076. 

  2076. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    2077. 

  2077. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    2078. 

  2078. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    2079. 

  2079. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    2080. 

  2080. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    2081. 

  2081. Metafunction Class</a> whose first argument will be the type of the
    2082. 

  2082. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    2083. 

  2083. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.  If
    2084. 

  2084. <tt class="docutils literal">restriction</tt> uses this form, then the type of the generated name
    2085. 

  2085. <tt class="docutils literal"><span class="pre">argument-name</span> ## _type</tt> will be computed in terms of the <strong>target
    2086. 

  2086. type</strong>, and the generated reference <tt class="docutils literal"><span class="pre">argument-name</span></tt> (but not its
    2087. 

  2087. corresponding entry in <tt class="docutils literal">args</tt>) will be cast to that type.</li>
    2088. 

  2088. </ul>
    2089. 

  2089. <p><strong>Approximate expansion:</strong></p>
    2090. 

  2090. <p>Where:</p>
    2091. 

  2091. <ul class="simple">
    2092. 

  2092. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    2093. 

  2093. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    2094. 

  2094. </ul>
    2095. 

  2095. <pre class="literal-block">
    2096. 

  2096. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    2097. 

  2097. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    2098. 

  2098. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    2099. 

  2099. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    2100. 

  2100. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    2101. 

  2101. template &lt;typename Args&gt;
    2102. 

  2102. using boost_param_result_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    2103. 

  2103. 

  2104. // If <strong>result</strong> is a simple return type:
    2105. 

  2105. template &lt;typename Args&gt;
    2106. 

  2106. struct boost_param_result_ ## __LINE__ ## <strong>name</strong>
    2107. 

  2107. {
    2108. 

  2108.     typedef <strong>result</strong> type;
    2109. 

  2109. };
    2110. 

  2110. 

  2111. struct boost_param_params_ ## __LINE__ ## <strong>name</strong>
    2112. 

  2112.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    2113. 

  2113.         <em>list of parameter specifications, based on arguments</em>
    2114. 

  2114.     &gt;
    2115. 

  2115. {
    2116. 

  2116. };
    2117. 

  2117. 

  2118. typedef boost_param_params_ ## __LINE__ ## <strong>name</strong>
    2119. 

  2119.     boost_param_parameters_ ## __LINE__ ## <strong>name</strong>;
    2120. 

  2120. 

  2121. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    2122. 

  2122. <strong>result</strong> <strong>name</strong>(
    2123. 

  2123.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    2124. 

  2124.   , typename boost_param_parameters_ ## __LINE__ ## <strong>name</strong>
    2125. 

  2125.     ::match&lt;A0, …, A ## <strong>n</strong>&gt;::type
    2126. 

  2126.     = boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()
    2127. 

  2127. )
    2128. 

  2128. {
    2129. 

  2129.     return this-&gt;boost_param_impl ## __LINE__ ## <strong>name</strong>(
    2130. 

  2130.         boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()(
    2131. 

  2131.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    2132. 

  2132.           , …
    2133. 

  2133.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    2134. 

  2134.         )
    2135. 

  2135.     );
    2136. 

  2136. }
    2137. 

  2137. 

  2138. <span class="vellipsis">⋮</span>
    2139. 

  2139. 

  2140. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    2141. 

  2141. <strong>result</strong> <strong>name</strong>(
    2142. 

  2142.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    2143. 

  2143.   , typename boost_param_parameters_ ## __LINE__ ## <strong>name</strong>
    2144. 

  2144.     ::match&lt;A0, …, A ## <strong>m</strong>&gt;::type
    2145. 

  2145.     = boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()
    2146. 

  2146. )
    2147. 

  2147. {
    2148. 

  2148.     return this-&gt;boost_param_impl ## __LINE__ ## <strong>name</strong>(
    2149. 

  2149.         boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()(
    2150. 

  2150.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    2151. 

  2151.           , …
    2152. 

  2152.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    2153. 

  2153.         )
    2154. 

  2154.     );
    2155. 

  2155. }
    2156. 

  2156. 

  2157. template &lt;typename Args&gt;
    2158. 

  2158. typename boost_param_result_ ## __LINE__ ## <strong>name</strong>&lt;Args&gt;::type
    2159. 

  2159.     boost_param_impl ## __LINE__ ## <strong>name</strong>(Args const&amp; args)
    2160. 

  2160. {
    2161. 

  2161.     return this-&gt;boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    2162. 

  2162.         static_cast&lt;
    2163. 

  2163.             typename boost_param_result_ ## __LINE__ ## <strong>name</strong>&lt;
    2164. 

  2164.                 Args
    2165. 

  2165.             &gt;::type(*)()
    2166. 

  2166.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    2167. 

  2167.       , args
    2168. 

  2168.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2169. 

  2169.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2170. 

  2170.                 Args
    2171. 

  2171.               , <em>keyword tag type of required parameter</em> ## <strong>0</strong>
    2172. 

  2172.             &gt;::type
    2173. 

  2173.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>0</strong>])
    2174. 

  2174.       , …
    2175. 

  2175.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2176. 

  2176.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2177. 

  2177.                 Args
    2178. 

  2178.               , <em>keyword tag type of required parameter</em> ## <strong>n</strong>
    2179. 

  2179.             &gt;::type
    2180. 

  2180.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>n</strong>])
    2181. 

  2181.     );
    2182. 

  2182. }
    2183. 

  2183. 

  2184. template &lt;
    2185. 

  2185.     typename ResultType
    2186. 

  2186.   , typename Args
    2187. 

  2187.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    2188. 

  2188.   , …
    2189. 

  2189.   , typename <em>argument name</em> ## <strong>n</strong> ## _type
    2190. 

  2190. &gt;
    2191. 

  2191. ResultType
    2192. 

  2192.     boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    2193. 

  2193.         (ResultType(*)())
    2194. 

  2194.       , Args const&amp; args
    2195. 

  2195.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    2196. 

  2196.       , …
    2197. 

  2197.       , <em>argument name</em> ## <strong>n</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>n</strong>
    2198. 

  2198.     )
    2199. 

  2199. {
    2200. 

  2200.     return this-&gt;boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    2201. 

  2201.         static_cast&lt;ResultType(*)()&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    2202. 

  2202.       , (args, <em>keyword object of optional parameter</em> ## <strong>n + 1</strong> =
    2203. 

  2203.             <em>default value of optional parameter</em> ## <strong>n + 1</strong>
    2204. 

  2204.         )
    2205. 

  2205.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>0</strong> ## _type&gt;(
    2206. 

  2206.             <em>argument name</em> ## <strong>0</strong>
    2207. 

  2207.         )
    2208. 

  2208.       , …
    2209. 

  2209.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>n</strong> ## _type&gt;(
    2210. 

  2210.             <em>argument name</em> ## <strong>n</strong>
    2211. 

  2211.         )
    2212. 

  2212.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2213. 

  2213.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2214. 

  2214.                 Args
    2215. 

  2215.               , <em>keyword tag type of optional parameter</em> ## <strong>n + 1</strong>
    2216. 

  2216.             &gt;::type
    2217. 

  2217.         &gt;(<em>default value of optional parameter</em> ## <strong>n + 1</strong>)
    2218. 

  2218.     );
    2219. 

  2219. }
    2220. 

  2220. 

  2221. <span class="vellipsis">⋮</span>
    2222. 

  2222. 

  2223. template &lt;
    2224. 

  2224.     typename ResultType
    2225. 

  2225.   , typename Args
    2226. 

  2226.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    2227. 

  2227.   , …
    2228. 

  2228.   , typename <em>argument name</em> ## <strong>m</strong> ## _type
    2229. 

  2229. &gt;
    2230. 

  2230. ResultType
    2231. 

  2231.     boost_param_dispatch_0boost_ ## __LINE__ ## <strong>name</strong>(
    2232. 

  2232.         (ResultType(*)())
    2233. 

  2233.       , Args const&amp; args
    2234. 

  2234.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    2235. 

  2235.       , …
    2236. 

  2236.       , <em>argument name</em> ## <strong>m</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>m</strong>
    2237. 

  2237.     )
    2238. 

  2238. </pre>
    2239. 

  2239. </div>
    2240. 

  2240. <div class="section" id="boost-parameter-const-member-function-result-name-tag-ns-arguments">
    2241. 

  2241. <span id="boost-parameter-const-member-function"></span><h2><a class="toc-backref" href="#id59">7.3&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_CONST_MEMBER_FUNCTION(result, name, tag_ns, arguments)</tt></a></h2>
    2242. 

  2242. <table class="docutils field-list" frame="void" rules="none">
    2243. 

  2243. <col class="field-name" />
    2244. 

  2244. <col class="field-body" />
    2245. 

  2245. <tbody valign="top">
    2246. 

  2246. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    2247. 

  2247. </tr>
    2248. 

  2248. </tbody>
    2249. 

  2249. </table>
    2250. 

  2250. <p>Generates a member function that can take in positional arguments, composed
    2251. 

  2251. arguments, named arguments, and deduced arguments.</p>
    2252. 

  2252. <table class="docutils field-list" frame="void" rules="none">
    2253. 

  2253. <col class="field-name" />
    2254. 

  2254. <col class="field-body" />
    2255. 

  2255. <tbody valign="top">
    2256. 

  2256. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    2257. 

  2257. </tr>
    2258. 

  2258. </tbody>
    2259. 

  2259. </table>
    2260. 

  2260. <p>The return type of each of the following function templates falls under a
    2261. 

  2261. different value category.</p>
    2262. 

  2262. <pre class="literal-block">
    2263. 

  2263. template &lt;std::size_t N&gt;
    2264. 

  2264. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    2265. 

  2265. {
    2266. 

  2266.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    2267. 

  2267. }
    2268. 

  2268. 

  2269. template &lt;std::size_t N&gt;
    2270. 

  2270. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    2271. 

  2271. {
    2272. 

  2272.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    2273. 

  2273. }
    2274. 

  2274. 

  2275. template &lt;std::size_t N&gt;
    2276. 

  2276. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    2277. 

  2277. {
    2278. 

  2278.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    2279. 

  2279.     return lset;
    2280. 

  2280. }
    2281. 

  2281. 

  2282. template &lt;std::size_t N&gt;
    2283. 

  2283. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    2284. 

  2284. {
    2285. 

  2285.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    2286. 

  2286.     return clset;
    2287. 

  2287. }
    2288. 

  2288. </pre>
    2289. 

  2289. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    2290. 

  2290. to return the correct value category when passed in an object returned by one
    2291. 

  2291. of the functions defined above.  Assume that
    2292. 

  2292. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    2293. 

  2293. <pre class="literal-block">
    2294. 

  2294. enum invoked
    2295. 

  2295. {
    2296. 

  2296.     passed_by_lvalue_reference_to_const
    2297. 

  2297.   , passed_by_lvalue_reference
    2298. 

  2298.   , passed_by_rvalue_reference_to_const
    2299. 

  2299.   , passed_by_rvalue_reference
    2300. 

  2300. };
    2301. 

  2301. 

  2302. struct U
    2303. 

  2303. {
    2304. 

  2304.     template &lt;std::size_t N&gt;
    2305. 

  2305.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    2306. 

  2306.     {
    2307. 

  2307.         return passed_by_lvalue_reference_to_const;
    2308. 

  2308.     }
    2309. 

  2309. 

  2310.     template &lt;std::size_t N&gt;
    2311. 

  2311.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    2312. 

  2312.     {
    2313. 

  2313.         return passed_by_lvalue_reference;
    2314. 

  2314.     }
    2315. 

  2315. 

  2316.     template &lt;std::size_t N&gt;
    2317. 

  2317.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    2318. 

  2318.     {
    2319. 

  2319.         return passed_by_rvalue_reference_to_const;
    2320. 

  2320.     }
    2321. 

  2321. 

  2322.     template &lt;std::size_t N&gt;
    2323. 

  2323.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    2324. 

  2324.     {
    2325. 

  2325.         return passed_by_rvalue_reference;
    2326. 

  2326.     }
    2327. 

  2327. };
    2328. 

  2328. </pre>
    2329. 

  2329. <p>Define the named parameters that will comprise the argument specification that
    2330. 

  2330. this macro will use.  Ensure that all their tag types are in the same
    2331. 

  2331. namespace, which is <tt class="docutils literal">kw</tt> in this case.  The identifiers with leading
    2332. 

  2332. underscores can be passed to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    2333. 

  2333. same argument to which the corresponding named parameter (without underscores)
    2334. 

  2334. is bound, as will be shown later.</p>
    2335. 

  2335. <pre class="literal-block">
    2336. 

  2336. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw) in(lrc))
    2337. 

  2337. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw) in_out(lr))
    2338. 

  2338. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw) in(rrc))
    2339. 

  2339. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw) consume(rr))
    2340. 

  2340. </pre>
    2341. 

  2341. <p>Use the macro as a substitute for a normal <tt class="docutils literal">const</tt> member function
    2342. 

  2342. header.  Enclose the return type <tt class="docutils literal">bool</tt> in parentheses.  For each parameter,
    2343. 

  2343. also enclose the expected value type in parentheses.  Since the value types
    2344. 

  2344. are mutually exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    2345. 

  2345. clause.  Otherwise, just as with a normal function, the order in which you
    2346. 

  2346. specify the parameters determines their position.  Also, just as with a normal
    2347. 

  2347. function, optional parameters have default values, whereas required parameters
    2348. 

  2348. do not.  Within the function body, either simply use the parameter name or
    2349. 

  2349. pass the matching identifier with the leading underscore to the bracket
    2350. 

  2350. operator of <tt class="docutils literal">args</tt> to extract the corresponding argument.  Note that the
    2351. 

  2351. second method doesn't require <tt class="docutils literal"><span class="pre">std::forward</span></tt> to preserve value categories.</p>
    2352. 

  2352. <pre class="literal-block">
    2353. 

  2353. struct B
    2354. 

  2354. {
    2355. 

  2355.     B()
    2356. 

  2356.     {
    2357. 

  2357.     }
    2358. 

  2358. 

  2359.     BOOST_PARAMETER_CONST_MEMBER_FUNCTION((bool), evaluate, kw,
    2360. 

  2360.         (deduced
    2361. 

  2361.             (required
    2362. 

  2362.                 (lrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;1&gt;))
    2363. 

  2363.                 (lr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;2&gt;))
    2364. 

  2364.             )
    2365. 

  2365.             (optional
    2366. 

  2366.                 (rrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;3&gt;), rvalue_const_bitset&lt;2&gt;())
    2367. 

  2367.                 (rr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;4&gt;), rvalue_bitset&lt;3&gt;())
    2368. 

  2368.             )
    2369. 

  2369.         )
    2370. 

  2370.     )
    2371. 

  2371.     {
    2372. 

  2372.         BOOST_TEST_EQ(
    2373. 

  2373.             passed_by_lvalue_reference_to_const
    2374. 

  2374.           , U::evaluate_category&lt;0&gt;(lrc)
    2375. 

  2375.         );
    2376. 

  2376.         BOOST_TEST_EQ(
    2377. 

  2377.             passed_by_lvalue_reference
    2378. 

  2378.           , U::evaluate_category&lt;1&gt;(lr)
    2379. 

  2379.         );
    2380. 

  2380.         BOOST_TEST_EQ(
    2381. 

  2381.             passed_by_rvalue_reference_to_const
    2382. 

  2382.           , U::evaluate_category&lt;2&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;rrc0_type&gt;(rrc0))
    2383. 

  2383.         );
    2384. 

  2384.         BOOST_TEST_EQ(
    2385. 

  2385.             passed_by_rvalue_reference
    2386. 

  2386.           , U::evaluate_category&lt;3&gt;(args[_rr0])
    2387. 

  2387.         );
    2388. 

  2388. 

  2389.         return true;
    2390. 

  2390.     }
    2391. 

  2391. };
    2392. 

  2392. </pre>
    2393. 

  2393. <p>The following function calls are legal.</p>
    2394. 

  2394. <pre class="literal-block">
    2395. 

  2395. B const b = B();
    2396. 

  2396. b.evaluate(  // positional arguments
    2397. 

  2397.     lvalue_const_bitset&lt;0&gt;()
    2398. 

  2398.   , lvalue_bitset&lt;1&gt;()
    2399. 

  2399.   , rvalue_const_bitset&lt;2&gt;()
    2400. 

  2400.   , rvalue_bitset&lt;3&gt;()
    2401. 

  2401. );
    2402. 

  2402. b.evaluate(  // positional arguments
    2403. 

  2403.     lvalue_const_bitset&lt;0&gt;()
    2404. 

  2404.   , lvalue_bitset&lt;1&gt;()
    2405. 

  2405. );
    2406. 

  2406. b.evaluate((  // composed arguments
    2407. 

  2407.     _rr0 = rvalue_bitset&lt;3&gt;()
    2408. 

  2408.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    2409. 

  2409.   , _lr0 = lvalue_bitset&lt;1&gt;()
    2410. 

  2410.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    2411. 

  2411. ));
    2412. 

  2412. b.evaluate(  // named arguments
    2413. 

  2413.     _rr0 = rvalue_bitset&lt;3&gt;()
    2414. 

  2414.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    2415. 

  2415.   , _lr0 = lvalue_bitset&lt;1&gt;()
    2416. 

  2416.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    2417. 

  2417. );
    2418. 

  2418. b.evaluate(  // named arguments
    2419. 

  2419.     _lr0 = lvalue_bitset&lt;1&gt;()
    2420. 

  2420.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    2421. 

  2421. );
    2422. 

  2422. </pre>
    2423. 

  2423. <p>Because the parameters were wrapped in a <tt class="docutils literal">(deduced …)</tt> clause, the following
    2424. 

  2424. function calls are also legal.</p>
    2425. 

  2425. <pre class="literal-block">
    2426. 

  2426. b.evaluate(  // deduced arguments
    2427. 

  2427.     rvalue_bitset&lt;3&gt;()
    2428. 

  2428.   , lvalue_const_bitset&lt;0&gt;()
    2429. 

  2429.   , lvalue_bitset&lt;1&gt;()
    2430. 

  2430.   , rvalue_const_bitset&lt;2&gt;()
    2431. 

  2431. );
    2432. 

  2432. b.evaluate(  // deduced arguments
    2433. 

  2433.     lvalue_bitset&lt;1&gt;()
    2434. 

  2434.   , lvalue_const_bitset&lt;0&gt;()
    2435. 

  2435. );
    2436. 

  2436. </pre>
    2437. 

  2437. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> test program demonstrates proper usage of this macro.</p>
    2438. 

  2438. <p><strong>Macro parameters:</strong></p>
    2439. 

  2439. <ul class="simple">
    2440. 

  2440. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    2441. 

  2441. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    2442. 

  2442. generated forwarding functions.</li>
    2443. 

  2443. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    2444. 

  2444. function resides.</li>
    2445. 

  2445. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    2446. 

  2446. <em>argument-specifiers</em>, as defined below.</li>
    2447. 

  2447. </ul>
    2448. 

  2448. <p><strong>Argument specifiers syntax:</strong></p>
    2449. 

  2449. <pre class="literal-block">
    2450. 

  2450. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    2451. 

  2451. 

  2452. specifier-group0 ::= <em>specifier-group1</em> |
    2453. 

  2453.     (
    2454. 

  2454.         '<strong>(</strong>' '<strong>deduced</strong>'
    2455. 

  2455.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    2456. 

  2456.         '<strong>)</strong>'
    2457. 

  2457.     )
    2458. 

  2458. 

  2459. specifier-group1 ::=
    2460. 

  2460.     (
    2461. 

  2461.         '<strong>(</strong>' '<strong>optional</strong>'
    2462. 

  2462.             <em>optional-specifier</em> {<em>optional-specifier</em>}
    2463. 

  2463.         '<strong>)</strong>'
    2464. 

  2464.     ) | (
    2465. 

  2465.         '<strong>(</strong>' '<strong>required</strong>'
    2466. 

  2466.             <em>required-specifier</em> {<em>required-specifier</em>}
    2467. 

  2467.         '<strong>)</strong>'
    2468. 

  2468.     )
    2469. 

  2469. 

  2470. optional-specifier ::=
    2471. 

  2471.     '<strong>(</strong>'
    2472. 

  2472.         <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> '<strong>,</strong>' <em>default-value</em>
    2473. 

  2473.     ')'
    2474. 

  2474. 

  2475. required-specifier ::=
    2476. 

  2476.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    2477. 

  2477. 

  2478. restriction ::=
    2479. 

  2479.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    2480. 

  2480.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    2481. 

  2481.     '<strong>*</strong>'
    2482. 

  2482. </pre>
    2483. 

  2483. <ul class="simple">
    2484. 

  2484. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    2485. 

  2485. <li><tt class="docutils literal"><span class="pre">default-value</span></tt> is any valid C++ expression; if necessary, user code can
    2486. 

  2486. compute it in terms of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>, where <tt class="docutils literal"><span class="pre">previous-name</span></tt>
    2487. 

  2487. is the <tt class="docutils literal"><span class="pre">argument-name</span></tt> in a previous <tt class="docutils literal"><span class="pre">specifier-group0</span></tt> or
    2488. 

  2488. <tt class="docutils literal"><span class="pre">specifier-group1</span></tt>.  <em>This expression will be invoked exactly once.</em></li>
    2489. 

  2489. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    2490. 

  2490. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    2491. 

  2491. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    2492. 

  2492. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    2493. 

  2493. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    2494. 

  2494. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    2495. 

  2495. Metafunction Class</a> whose first argument will be the type of the
    2496. 

  2496. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    2497. 

  2497. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.  If
    2498. 

  2498. <tt class="docutils literal">restriction</tt> uses this form, then the type of the generated name
    2499. 

  2499. <tt class="docutils literal"><span class="pre">argument-name</span> ## _type</tt> will be computed in terms of the <strong>target
    2500. 

  2500. type</strong>, and the generated reference <tt class="docutils literal"><span class="pre">argument-name</span></tt> (but not its
    2501. 

  2501. corresponding entry in <tt class="docutils literal">args</tt>) will be cast to that type.</li>
    2502. 

  2502. </ul>
    2503. 

  2503. <p><strong>Approximate expansion:</strong></p>
    2504. 

  2504. <p>Where:</p>
    2505. 

  2505. <ul class="simple">
    2506. 

  2506. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    2507. 

  2507. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    2508. 

  2508. </ul>
    2509. 

  2509. <pre class="literal-block">
    2510. 

  2510. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    2511. 

  2511. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    2512. 

  2512. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    2513. 

  2513. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    2514. 

  2514. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    2515. 

  2515. template &lt;typename Args&gt;
    2516. 

  2516. using boost_param_result_const_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    2517. 

  2517. 

  2518. // If <strong>result</strong> is a simple return type:
    2519. 

  2519. template &lt;typename Args&gt;
    2520. 

  2520. struct boost_param_result_const_ ## __LINE__ ## <strong>name</strong>
    2521. 

  2521. {
    2522. 

  2522.     typedef <strong>result</strong> type;
    2523. 

  2523. };
    2524. 

  2524. 

  2525. struct boost_param_params_const_ ## __LINE__ ## <strong>name</strong>
    2526. 

  2526.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    2527. 

  2527.         <em>list of parameter specifications, based on arguments</em>
    2528. 

  2528.     &gt;
    2529. 

  2529. {
    2530. 

  2530. };
    2531. 

  2531. 

  2532. typedef boost_param_params_const_ ## __LINE__ ## <strong>name</strong>
    2533. 

  2533.     boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>;
    2534. 

  2534. 

  2535. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    2536. 

  2536. <strong>result</strong> <strong>name</strong>(
    2537. 

  2537.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    2538. 

  2538.   , typename boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>
    2539. 

  2539.     ::match&lt;A0, …, A ## <strong>n</strong>&gt;::type
    2540. 

  2540.     = boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>()
    2541. 

  2541. ) const
    2542. 

  2542. {
    2543. 

  2543.     return this-&gt;boost_param_impl_const ## __LINE__ ## <strong>name</strong>(
    2544. 

  2544.         boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>(
    2545. 

  2545.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    2546. 

  2546.           , …
    2547. 

  2547.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    2548. 

  2548.         )
    2549. 

  2549.     );
    2550. 

  2550. }
    2551. 

  2551. 

  2552. <span class="vellipsis">⋮</span>
    2553. 

  2553. 

  2554. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    2555. 

  2555. <strong>result</strong> <strong>name</strong>(
    2556. 

  2556.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    2557. 

  2557.   , typename boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>
    2558. 

  2558.     ::match&lt;A0, …, A ## <strong>m</strong>&gt;::type
    2559. 

  2559.     = boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>()
    2560. 

  2560. ) const
    2561. 

  2561. {
    2562. 

  2562.     return this-&gt;boost_param_impl_const ## __LINE__ ## <strong>name</strong>(
    2563. 

  2563.         boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>()(
    2564. 

  2564.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    2565. 

  2565.           , …
    2566. 

  2566.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    2567. 

  2567.         )
    2568. 

  2568.     );
    2569. 

  2569. }
    2570. 

  2570. 

  2571. template &lt;typename Args&gt;
    2572. 

  2572. typename boost_param_result_const_ ## __LINE__ ## <strong>name</strong>&lt;Args&gt;::type
    2573. 

  2573.     boost_param_impl_const ## __LINE__ ## <strong>name</strong>(Args const&amp; args) const
    2574. 

  2574. {
    2575. 

  2575.     return this-&gt;
    2576. 

  2576.     boost_param_dispatch_const_0boost_ ## __LINE__ ## <strong>name</strong>(
    2577. 

  2577.         static_cast&lt;
    2578. 

  2578.             typename boost_param_result_const_ ## __LINE__ ## <strong>name</strong>&lt;
    2579. 

  2579.                 Args
    2580. 

  2580.             &gt;::type(*)()
    2581. 

  2581.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    2582. 

  2582.       , args
    2583. 

  2583.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2584. 

  2584.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2585. 

  2585.                 Args
    2586. 

  2586.               , <em>keyword tag type of required parameter</em> ## <strong>0</strong>
    2587. 

  2587.             &gt;::type
    2588. 

  2588.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>0</strong>])
    2589. 

  2589.       , …
    2590. 

  2590.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2591. 

  2591.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2592. 

  2592.                 Args
    2593. 

  2593.               , <em>keyword tag type of required parameter</em> ## <strong>n</strong>
    2594. 

  2594.             &gt;::type
    2595. 

  2595.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>n</strong>])
    2596. 

  2596.     );
    2597. 

  2597. }
    2598. 

  2598. 

  2599. template &lt;
    2600. 

  2600.     typename ResultType
    2601. 

  2601.   , typename Args
    2602. 

  2602.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    2603. 

  2603.   , …
    2604. 

  2604.   , typename <em>argument name</em> ## <strong>n</strong> ## _type
    2605. 

  2605. &gt;
    2606. 

  2606. ResultType
    2607. 

  2607.     boost_param_dispatch_const_0boost_ ## __LINE__ ## <strong>name</strong>(
    2608. 

  2608.         (ResultType(*)())
    2609. 

  2609.       , Args const&amp; args
    2610. 

  2610.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    2611. 

  2611.       , …
    2612. 

  2612.       , <em>argument name</em> ## <strong>n</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>n</strong>
    2613. 

  2613.     ) const
    2614. 

  2614. {
    2615. 

  2615.     return this-&gt;
    2616. 

  2616.     boost_param_dispatch_const_0boost_ ## __LINE__ ## <strong>name</strong>(
    2617. 

  2617.         static_cast&lt;ResultType(*)()&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    2618. 

  2618.       , (args, <em>keyword object of optional parameter</em> ## <strong>n + 1</strong> =
    2619. 

  2619.             <em>default value of optional parameter</em> ## <strong>n + 1</strong>
    2620. 

  2620.         )
    2621. 

  2621.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>0</strong> ## _type&gt;(
    2622. 

  2622.             <em>argument name</em> ## <strong>0</strong>
    2623. 

  2623.         )
    2624. 

  2624.       , …
    2625. 

  2625.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>n</strong> ## _type&gt;(
    2626. 

  2626.             <em>argument name</em> ## <strong>n</strong>
    2627. 

  2627.         )
    2628. 

  2628.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2629. 

  2629.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2630. 

  2630.                 Args
    2631. 

  2631.               , <em>keyword tag type of optional parameter</em> ## <strong>n + 1</strong>
    2632. 

  2632.             &gt;::type
    2633. 

  2633.         &gt;(<em>default value of optional parameter</em> ## <strong>n + 1</strong>)
    2634. 

  2634.     );
    2635. 

  2635. }
    2636. 

  2636. 

  2637. <span class="vellipsis">⋮</span>
    2638. 

  2638. 

  2639. template &lt;
    2640. 

  2640.     typename ResultType
    2641. 

  2641.   , typename Args
    2642. 

  2642.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    2643. 

  2643.   , …
    2644. 

  2644.   , typename <em>argument name</em> ## <strong>m</strong> ## _type
    2645. 

  2645. &gt;
    2646. 

  2646. ResultType
    2647. 

  2647.     boost_param_dispatch_const_0boost_ ## __LINE__ ## <strong>name</strong>(
    2648. 

  2648.         (ResultType(*)())
    2649. 

  2649.       , Args const&amp; args
    2650. 

  2650.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    2651. 

  2651.       , …
    2652. 

  2652.       , <em>argument name</em> ## <strong>m</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>m</strong>
    2653. 

  2653.     ) const
    2654. 

  2654. </pre>
    2655. 

  2655. </div>
    2656. 

  2656. <div class="section" id="boost-parameter-function-call-operator-result-tag-namespace-arguments">
    2657. 

  2657. <span id="boost-parameter-function-call-operator"></span><h2><a class="toc-backref" href="#id60">7.4&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_FUNCTION_CALL_OPERATOR(result, tag_namespace, arguments)</tt></a></h2>
    2658. 

  2658. <table class="docutils field-list" frame="void" rules="none">
    2659. 

  2659. <col class="field-name" />
    2660. 

  2660. <col class="field-body" />
    2661. 

  2661. <tbody valign="top">
    2662. 

  2662. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    2663. 

  2663. </tr>
    2664. 

  2664. </tbody>
    2665. 

  2665. </table>
    2666. 

  2666. <p>Generates a function call operator that can take in positional arguments,
    2667. 

  2667. composed arguments, named arguments, and deduced arguments.</p>
    2668. 

  2668. <table class="docutils field-list" frame="void" rules="none">
    2669. 

  2669. <col class="field-name" />
    2670. 

  2670. <col class="field-body" />
    2671. 

  2671. <tbody valign="top">
    2672. 

  2672. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    2673. 

  2673. </tr>
    2674. 

  2674. </tbody>
    2675. 

  2675. </table>
    2676. 

  2676. <p>Define the named parameters that will comprise the argument specification that
    2677. 

  2677. this macro will use.  Ensure that all their tag types are in the same
    2678. 

  2678. namespace, which is <tt class="docutils literal">tag</tt> by default.</p>
    2679. 

  2679. <pre class="literal-block">
    2680. 

  2680. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(y)
    2681. 

  2681. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(z)
    2682. 

  2682. </pre>
    2683. 

  2683. <p>Use the macro as a substitute for a normal function call operator
    2684. 

  2684. header.  Enclose the return type in parentheses.  For each parameter, also
    2685. 

  2685. enclose the expected value type in parentheses.  Since the value types are
    2686. 

  2686. mutually exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    2687. 

  2687. clause.  This is especially useful when implementing multiple
    2688. 

  2688. Boost.Parameter-enabled function call operator overloads.</p>
    2689. 

  2689. <pre class="literal-block">
    2690. 

  2690. class char_reader
    2691. 

  2691. {
    2692. 

  2692.     int index;
    2693. 

  2693.     char const* key;
    2694. 

  2694. 

  2695.  public:
    2696. 

  2696.     explicit char_reader(char const* k) : index(0), key(k)
    2697. 

  2697.     {
    2698. 

  2698.     }
    2699. 

  2699. 

  2700.     BOOST_PARAMETER_FUNCTION_CALL_OPERATOR((void), tag,
    2701. 

  2701.         (deduced
    2702. 

  2702.             (required
    2703. 

  2703.                 (y, (int))
    2704. 

  2704.                 (z, (char const*))
    2705. 

  2705.             )
    2706. 

  2706.         )
    2707. 

  2707.     )
    2708. 

  2708.     {
    2709. 

  2709.         this-&gt;index = y;
    2710. 

  2710.         this-&gt;key = z;
    2711. 

  2711.     }
    2712. 

  2712. 

  2713.     <a class="reference internal" href="#boost-parameter-const-function-call-operator"><tt class="docutils literal">BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR</tt></a>((char), tag,
    2714. 

  2714.         (deduced
    2715. 

  2715.             (required
    2716. 

  2716.                 (y, (bool))
    2717. 

  2717.                 (z, (<a class="reference external" href="http://en.cppreference.com/w/cpp/container/map">std::map</a>&lt;char const*, <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>&gt;))
    2718. 

  2718.             )
    2719. 

  2719.         )
    2720. 

  2720.     )
    2721. 

  2721.     {
    2722. 

  2722.         return y ? (
    2723. 

  2723.             (z.find(this-&gt;key)-&gt;second)[this-&gt;index]
    2724. 

  2724.         ) : this-&gt;key[this-&gt;index];
    2725. 

  2725.     }
    2726. 

  2726. };
    2727. 

  2727. </pre>
    2728. 

  2728. <p>As with regular argument-dependent lookup, the value types of the arguments
    2729. 

  2729. passed in determine which function call operator overload gets invoked.</p>
    2730. 

  2730. <pre class="literal-block">
    2731. 

  2731. char const* keys[] = {&quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;};
    2732. 

  2732. <a class="reference external" href="http://en.cppreference.com/w/cpp/container/map">std::map</a>&lt;char const*, <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>&gt; k2s;
    2733. 

  2733. k2s[keys[0]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;qux&quot;);
    2734. 

  2734. k2s[keys[1]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;wmb&quot;);
    2735. 

  2735. k2s[keys[2]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;zxc&quot;);
    2736. 

  2736. char_reader r(keys[0]);
    2737. 

  2737. 

  2738. // positional arguments
    2739. 

  2739. BOOST_TEST_EQ('q', (r(true, k2s)));
    2740. 

  2740. BOOST_TEST_EQ('f', (r(false, k2s)));
    2741. 

  2741. 

  2742. // named arguments
    2743. 

  2743. r(_z = keys[1], _y = 1);
    2744. 

  2744. BOOST_TEST_EQ('m', (r(_z = k2s, _y = true)));
    2745. 

  2745. BOOST_TEST_EQ('a', (r(_z = k2s, _y = false)));
    2746. 

  2746. 

  2747. // deduced arguments
    2748. 

  2748. r(keys[2], 2);
    2749. 

  2749. BOOST_TEST_EQ('c', (r(k2s, true)));
    2750. 

  2750. BOOST_TEST_EQ('z', (r(k2s, false)));
    2751. 

  2751. </pre>
    2752. 

  2752. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> and <a class="reference external" href="../../test/preprocessor_deduced.cpp">preprocessor_deduced.cpp</a> test programs
    2753. 

  2753. demonstrate proper usage of this macro.</p>
    2754. 

  2754. <p><strong>Macro parameters:</strong></p>
    2755. 

  2755. <ul class="simple">
    2756. 

  2756. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function call operator.</li>
    2757. 

  2757. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    2758. 

  2758. function call operator resides.</li>
    2759. 

  2759. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    2760. 

  2760. <em>argument-specifiers</em>, as defined below.</li>
    2761. 

  2761. </ul>
    2762. 

  2762. <p><strong>Argument specifiers syntax:</strong></p>
    2763. 

  2763. <pre class="literal-block">
    2764. 

  2764. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    2765. 

  2765. 

  2766. specifier-group0 ::= <em>specifier-group1</em> |
    2767. 

  2767.     (
    2768. 

  2768.         '<strong>(</strong>' '<strong>deduced</strong>'
    2769. 

  2769.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    2770. 

  2770.         '<strong>)</strong>'
    2771. 

  2771.     )
    2772. 

  2772. 

  2773. specifier-group1 ::=
    2774. 

  2774.     (
    2775. 

  2775.         '<strong>(</strong>' '<strong>optional</strong>'
    2776. 

  2776.             <em>optional-specifier</em> {<em>optional-specifier</em>}
    2777. 

  2777.         '<strong>)</strong>'
    2778. 

  2778.     ) | (
    2779. 

  2779.         '<strong>(</strong>' '<strong>required</strong>'
    2780. 

  2780.             <em>required-specifier</em> {<em>required-specifier</em>}
    2781. 

  2781.         '<strong>)</strong>'
    2782. 

  2782.     )
    2783. 

  2783. 

  2784. optional-specifier ::=
    2785. 

  2785.     '<strong>(</strong>'
    2786. 

  2786.         <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> '<strong>,</strong>' <em>default-value</em>
    2787. 

  2787.     ')'
    2788. 

  2788. 

  2789. required-specifier ::=
    2790. 

  2790.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    2791. 

  2791. 

  2792. restriction ::=
    2793. 

  2793.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    2794. 

  2794.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    2795. 

  2795.     '<strong>*</strong>'
    2796. 

  2796. </pre>
    2797. 

  2797. <ul class="simple">
    2798. 

  2798. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    2799. 

  2799. <li><tt class="docutils literal"><span class="pre">default-value</span></tt> is any valid C++ expression; if necessary, user code can
    2800. 

  2800. compute it in terms of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>, where <tt class="docutils literal"><span class="pre">previous-name</span></tt>
    2801. 

  2801. is the <tt class="docutils literal"><span class="pre">argument-name</span></tt> in a previous <tt class="docutils literal"><span class="pre">specifier-group0</span></tt> or
    2802. 

  2802. <tt class="docutils literal"><span class="pre">specifier-group1</span></tt>.  <em>This expression will be invoked exactly once.</em></li>
    2803. 

  2803. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    2804. 

  2804. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    2805. 

  2805. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    2806. 

  2806. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    2807. 

  2807. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    2808. 

  2808. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    2809. 

  2809. Metafunction Class</a> whose first argument will be the type of the
    2810. 

  2810. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    2811. 

  2811. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.  If
    2812. 

  2812. <tt class="docutils literal">restriction</tt> uses this form, then the type of the generated name
    2813. 

  2813. <tt class="docutils literal"><span class="pre">argument-name</span> ## _type</tt> will be computed in terms of the <strong>target
    2814. 

  2814. type</strong>, and the generated reference <tt class="docutils literal"><span class="pre">argument-name</span></tt> (but not its
    2815. 

  2815. corresponding entry in <tt class="docutils literal">args</tt>) will be cast to that type.</li>
    2816. 

  2816. </ul>
    2817. 

  2817. <p><strong>Approximate expansion:</strong></p>
    2818. 

  2818. <p>Where:</p>
    2819. 

  2819. <ul class="simple">
    2820. 

  2820. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    2821. 

  2821. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    2822. 

  2822. </ul>
    2823. 

  2823. <pre class="literal-block">
    2824. 

  2824. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    2825. 

  2825. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    2826. 

  2826. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    2827. 

  2827. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    2828. 

  2828. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    2829. 

  2829. template &lt;typename Args&gt;
    2830. 

  2830. using boost_param_result_ ## __LINE__ ## operator = <strong>result</strong>;
    2831. 

  2831. 

  2832. // If <strong>result</strong> is a simple return type:
    2833. 

  2833. template &lt;typename Args&gt;
    2834. 

  2834. struct boost_param_result_ ## __LINE__ ## operator
    2835. 

  2835. {
    2836. 

  2836.     typedef <strong>result</strong> type;
    2837. 

  2837. };
    2838. 

  2838. 

  2839. struct boost_param_params_ ## __LINE__ ## operator
    2840. 

  2840.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    2841. 

  2841.         <em>list of parameter specifications, based on arguments</em>
    2842. 

  2842.     &gt;
    2843. 

  2843. {
    2844. 

  2844. };
    2845. 

  2845. 

  2846. typedef boost_param_params_ ## __LINE__ ## operator
    2847. 

  2847.     boost_param_parameters_ ## __LINE__ ## operator;
    2848. 

  2848. 

  2849. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    2850. 

  2850. <strong>result</strong> operator()(
    2851. 

  2851.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    2852. 

  2852.   , typename boost_param_parameters_ ## __LINE__ ## operator::match&lt;
    2853. 

  2853.         A0, …, A ## <strong>n</strong>
    2854. 

  2854.     &gt;::type = boost_param_parameters_ ## __LINE__ ## operator()
    2855. 

  2855. )
    2856. 

  2856. {
    2857. 

  2857.     return this-&gt;boost_param_impl ## __LINE__ ## operator(
    2858. 

  2858.         boost_param_parameters_ ## __LINE__ ## operator()(
    2859. 

  2859.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    2860. 

  2860.           , …
    2861. 

  2861.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    2862. 

  2862.         )
    2863. 

  2863.     );
    2864. 

  2864. }
    2865. 

  2865. 

  2866. <span class="vellipsis">⋮</span>
    2867. 

  2867. 

  2868. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    2869. 

  2869. <strong>result</strong> operator()(
    2870. 

  2870.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    2871. 

  2871.   , typename boost_param_parameters_ ## __LINE__ ## operator::match&lt;
    2872. 

  2872.         A0, …, A ## <strong>m</strong>
    2873. 

  2873.     &gt;::type = boost_param_parameters_ ## __LINE__ ## operator()
    2874. 

  2874. )
    2875. 

  2875. {
    2876. 

  2876.     return this-&gt;boost_param_impl ## __LINE__ ## operator(
    2877. 

  2877.         boost_param_parameters_ ## __LINE__ ## operator()(
    2878. 

  2878.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    2879. 

  2879.           , …
    2880. 

  2880.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    2881. 

  2881.         )
    2882. 

  2882.     );
    2883. 

  2883. }
    2884. 

  2884. 

  2885. template &lt;typename Args&gt;
    2886. 

  2886. typename boost_param_result_ ## __LINE__ ## operator&lt;Args&gt;::type
    2887. 

  2887.     boost_param_impl ## __LINE__ ## operator(Args const&amp; args)
    2888. 

  2888. {
    2889. 

  2889.     return this-&gt;boost_param_dispatch_0boost_ ## __LINE__ ## operator(
    2890. 

  2890.         static_cast&lt;
    2891. 

  2891.             typename boost_param_result_ ## __LINE__ ## operator&lt;
    2892. 

  2892.                 Args
    2893. 

  2893.             &gt;::type(*)()
    2894. 

  2894.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    2895. 

  2895.       , args
    2896. 

  2896.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2897. 

  2897.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2898. 

  2898.                 Args
    2899. 

  2899.               , <em>keyword tag type of required parameter</em> ## <strong>0</strong>
    2900. 

  2900.             &gt;::type
    2901. 

  2901.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>0</strong>])
    2902. 

  2902.       , …
    2903. 

  2903.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2904. 

  2904.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2905. 

  2905.                 Args
    2906. 

  2906.               , <em>keyword tag type of required parameter</em> ## <strong>n</strong>
    2907. 

  2907.             &gt;::type
    2908. 

  2908.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>n</strong>])
    2909. 

  2909.     );
    2910. 

  2910. }
    2911. 

  2911. 

  2912. template &lt;
    2913. 

  2913.     typename ResultType
    2914. 

  2914.   , typename Args
    2915. 

  2915.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    2916. 

  2916.   , …
    2917. 

  2917.   , typename <em>argument name</em> ## <strong>n</strong> ## _type
    2918. 

  2918. &gt;
    2919. 

  2919. ResultType
    2920. 

  2920.     boost_param_dispatch_0boost_ ## __LINE__ ## operator(
    2921. 

  2921.         (ResultType(*)())
    2922. 

  2922.       , Args const&amp; args
    2923. 

  2923.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    2924. 

  2924.       , …
    2925. 

  2925.       , <em>argument name</em> ## <strong>n</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>n</strong>
    2926. 

  2926.     )
    2927. 

  2927. {
    2928. 

  2928.     return this-&gt;boost_param_dispatch_0boost_ ## __LINE__ ## operator(
    2929. 

  2929.         static_cast&lt;ResultType(*)()&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    2930. 

  2930.       , (args, <em>keyword object of optional parameter</em> ## <strong>n + 1</strong> =
    2931. 

  2931.             <em>default value of optional parameter</em> ## <strong>n + 1</strong>
    2932. 

  2932.         )
    2933. 

  2933.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>0</strong> ## _type&gt;(
    2934. 

  2934.             <em>argument name</em> ## <strong>0</strong>
    2935. 

  2935.         )
    2936. 

  2936.       , …
    2937. 

  2937.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>n</strong> ## _type&gt;(
    2938. 

  2938.             <em>argument name</em> ## <strong>n</strong>
    2939. 

  2939.         )
    2940. 

  2940.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    2941. 

  2941.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    2942. 

  2942.                 Args
    2943. 

  2943.               , <em>keyword tag type of optional parameter</em> ## <strong>n + 1</strong>
    2944. 

  2944.             &gt;::type
    2945. 

  2945.         &gt;(<em>default value of optional parameter</em> ## <strong>n + 1</strong>)
    2946. 

  2946.     );
    2947. 

  2947. }
    2948. 

  2948. 

  2949. <span class="vellipsis">⋮</span>
    2950. 

  2950. 

  2951. template &lt;
    2952. 

  2952.     typename ResultType
    2953. 

  2953.   , typename Args
    2954. 

  2954.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    2955. 

  2955.   , …
    2956. 

  2956.   , typename <em>argument name</em> ## <strong>m</strong> ## _type
    2957. 

  2957. &gt;
    2958. 

  2958. ResultType
    2959. 

  2959.     boost_param_dispatch_0boost_ ## __LINE__ ## operator(
    2960. 

  2960.         (ResultType(*)())
    2961. 

  2961.       , Args const&amp; args
    2962. 

  2962.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    2963. 

  2963.       , …
    2964. 

  2964.       , <em>argument name</em> ## <strong>m</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>m</strong>
    2965. 

  2965.     )
    2966. 

  2966. </pre>
    2967. 

  2967. </div>
    2968. 

  2968. <div class="section" id="boost-parameter-const-function-call-operator-result-tag-ns-arguments">
    2969. 

  2969. <span id="boost-parameter-const-function-call-operator"></span><h2><a class="toc-backref" href="#id61">7.5&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)</tt></a></h2>
    2970. 

  2970. <table class="docutils field-list" frame="void" rules="none">
    2971. 

  2971. <col class="field-name" />
    2972. 

  2972. <col class="field-body" />
    2973. 

  2973. <tbody valign="top">
    2974. 

  2974. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    2975. 

  2975. </tr>
    2976. 

  2976. </tbody>
    2977. 

  2977. </table>
    2978. 

  2978. <p>Generates a function call operator that can take in positional arguments,
    2979. 

  2979. composed arguments, named arguments, and deduced arguments.</p>
    2980. 

  2980. <table class="docutils field-list" frame="void" rules="none">
    2981. 

  2981. <col class="field-name" />
    2982. 

  2982. <col class="field-body" />
    2983. 

  2983. <tbody valign="top">
    2984. 

  2984. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    2985. 

  2985. </tr>
    2986. 

  2986. </tbody>
    2987. 

  2987. </table>
    2988. 

  2988. <p>The return type of each of the following function templates falls under a
    2989. 

  2989. different value category.</p>
    2990. 

  2990. <pre class="literal-block">
    2991. 

  2991. template &lt;std::size_t N&gt;
    2992. 

  2992. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    2993. 

  2993. {
    2994. 

  2994.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    2995. 

  2995. }
    2996. 

  2996. 

  2997. template &lt;std::size_t N&gt;
    2998. 

  2998. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    2999. 

  2999. {
    3000. 

  3000.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3001. 

  3001. }
    3002. 

  3002. 

  3003. template &lt;std::size_t N&gt;
    3004. 

  3004. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    3005. 

  3005. {
    3006. 

  3006.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3007. 

  3007.     return lset;
    3008. 

  3008. }
    3009. 

  3009. 

  3010. template &lt;std::size_t N&gt;
    3011. 

  3011. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    3012. 

  3012. {
    3013. 

  3013.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3014. 

  3014.     return clset;
    3015. 

  3015. }
    3016. 

  3016. </pre>
    3017. 

  3017. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    3018. 

  3018. to return the correct value category when passed in an object returned by one
    3019. 

  3019. of the functions defined above.  Assume that
    3020. 

  3020. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    3021. 

  3021. <pre class="literal-block">
    3022. 

  3022. enum invoked
    3023. 

  3023. {
    3024. 

  3024.     passed_by_lvalue_reference_to_const
    3025. 

  3025.   , passed_by_lvalue_reference
    3026. 

  3026.   , passed_by_rvalue_reference_to_const
    3027. 

  3027.   , passed_by_rvalue_reference
    3028. 

  3028. };
    3029. 

  3029. 

  3030. struct U
    3031. 

  3031. {
    3032. 

  3032.     template &lt;std::size_t N&gt;
    3033. 

  3033.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    3034. 

  3034.     {
    3035. 

  3035.         return passed_by_lvalue_reference_to_const;
    3036. 

  3036.     }
    3037. 

  3037. 

  3038.     template &lt;std::size_t N&gt;
    3039. 

  3039.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    3040. 

  3040.     {
    3041. 

  3041.         return passed_by_lvalue_reference;
    3042. 

  3042.     }
    3043. 

  3043. 

  3044.     template &lt;std::size_t N&gt;
    3045. 

  3045.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    3046. 

  3046.     {
    3047. 

  3047.         return passed_by_rvalue_reference_to_const;
    3048. 

  3048.     }
    3049. 

  3049. 

  3050.     template &lt;std::size_t N&gt;
    3051. 

  3051.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    3052. 

  3052.     {
    3053. 

  3053.         return passed_by_rvalue_reference;
    3054. 

  3054.     }
    3055. 

  3055. };
    3056. 

  3056. </pre>
    3057. 

  3057. <p>Define the named parameters that will comprise the argument specification that
    3058. 

  3058. this macro will use.  Ensure that all their tag types are in the same
    3059. 

  3059. namespace, which is <tt class="docutils literal">kw</tt> in this case.  The identifiers with leading
    3060. 

  3060. underscores can be passed to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    3061. 

  3061. same argument to which the corresponding named parameter (without underscores)
    3062. 

  3062. is bound, as will be shown later.</p>
    3063. 

  3063. <pre class="literal-block">
    3064. 

  3064. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw) in(lrc))
    3065. 

  3065. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw) in_out(lr))
    3066. 

  3066. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw) in(rrc))
    3067. 

  3067. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw) consume(rr))
    3068. 

  3068. </pre>
    3069. 

  3069. <p>Use the macro as a substitute for a normal <tt class="docutils literal">const</tt> function call operator
    3070. 

  3070. header.  Enclose the return type <tt class="docutils literal">bool</tt> in parentheses.  For each parameter,
    3071. 

  3071. also enclose the expected value type in parentheses.  Since the value types
    3072. 

  3072. are mutually exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    3073. 

  3073. clause.  Otherwise, just as with a normal function, the order in which you
    3074. 

  3074. specify the parameters determines their position.  Also, just as with a normal
    3075. 

  3075. function, optional parameters have default values, whereas required parameters
    3076. 

  3076. do not.  Within the function body, either simply use the parameter name or
    3077. 

  3077. pass the matching identifier with the leading underscore to the bracket
    3078. 

  3078. operator of <tt class="docutils literal">args</tt> to extract the corresponding argument.  Note that the
    3079. 

  3079. second method doesn't require <tt class="docutils literal"><span class="pre">std::forward</span></tt> to preserve value categories.</p>
    3080. 

  3080. <pre class="literal-block">
    3081. 

  3081. struct B
    3082. 

  3082. {
    3083. 

  3083.     B()
    3084. 

  3084.     {
    3085. 

  3085.     }
    3086. 

  3086. 

  3087.     BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR((bool), kw,
    3088. 

  3088.         (deduced
    3089. 

  3089.             (required
    3090. 

  3090.                 (lrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;1&gt;))
    3091. 

  3091.                 (lr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;2&gt;))
    3092. 

  3092.             )
    3093. 

  3093.             (optional
    3094. 

  3094.                 (rrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;3&gt;), rvalue_const_bitset&lt;2&gt;())
    3095. 

  3095.                 (rr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;4&gt;), rvalue_bitset&lt;3&gt;())
    3096. 

  3096.             )
    3097. 

  3097.         )
    3098. 

  3098.     )
    3099. 

  3099.     {
    3100. 

  3100.         BOOST_TEST_EQ(
    3101. 

  3101.             passed_by_lvalue_reference_to_const
    3102. 

  3102.           , U::evaluate_category&lt;0&gt;(lrc)
    3103. 

  3103.         );
    3104. 

  3104.         BOOST_TEST_EQ(
    3105. 

  3105.             passed_by_lvalue_reference
    3106. 

  3106.           , U::evaluate_category&lt;1&gt;(lr)
    3107. 

  3107.         );
    3108. 

  3108.         BOOST_TEST_EQ(
    3109. 

  3109.             passed_by_rvalue_reference_to_const
    3110. 

  3110.           , U::evaluate_category&lt;2&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;rrc0_type&gt;(rrc0))
    3111. 

  3111.         );
    3112. 

  3112.         BOOST_TEST_EQ(
    3113. 

  3113.             passed_by_rvalue_reference
    3114. 

  3114.           , U::evaluate_category&lt;3&gt;(args[_rr0])
    3115. 

  3115.         );
    3116. 

  3116. 

  3117.         return true;
    3118. 

  3118.     }
    3119. 

  3119. };
    3120. 

  3120. </pre>
    3121. 

  3121. <p>The following function calls are legal.</p>
    3122. 

  3122. <pre class="literal-block">
    3123. 

  3123. B const b = B();
    3124. 

  3124. b(  // positional arguments
    3125. 

  3125.     lvalue_const_bitset&lt;0&gt;()
    3126. 

  3126.   , lvalue_bitset&lt;1&gt;()
    3127. 

  3127.   , rvalue_const_bitset&lt;2&gt;()
    3128. 

  3128.   , rvalue_bitset&lt;3&gt;()
    3129. 

  3129. );
    3130. 

  3130. b(  // positional arguments
    3131. 

  3131.     lvalue_const_bitset&lt;0&gt;()
    3132. 

  3132.   , lvalue_bitset&lt;1&gt;()
    3133. 

  3133. );
    3134. 

  3134. b((  // composed arguments
    3135. 

  3135.     _rr0 = rvalue_bitset&lt;3&gt;()
    3136. 

  3136.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    3137. 

  3137.   , _lr0 = lvalue_bitset&lt;1&gt;()
    3138. 

  3138.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    3139. 

  3139. ));
    3140. 

  3140. b(  // named arguments
    3141. 

  3141.     _rr0 = rvalue_bitset&lt;3&gt;()
    3142. 

  3142.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    3143. 

  3143.   , _lr0 = lvalue_bitset&lt;1&gt;()
    3144. 

  3144.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    3145. 

  3145. );
    3146. 

  3146. b(  // named arguments
    3147. 

  3147.     _lr0 = lvalue_bitset&lt;1&gt;()
    3148. 

  3148.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    3149. 

  3149. );
    3150. 

  3150. </pre>
    3151. 

  3151. <p>Because the parameters were wrapped in a <tt class="docutils literal">(deduced …)</tt> clause, the following
    3152. 

  3152. function calls are also legal.</p>
    3153. 

  3153. <pre class="literal-block">
    3154. 

  3154. b(  // deduced arguments
    3155. 

  3155.     rvalue_bitset&lt;3&gt;()
    3156. 

  3156.   , lvalue_const_bitset&lt;0&gt;()
    3157. 

  3157.   , lvalue_bitset&lt;1&gt;()
    3158. 

  3158.   , rvalue_const_bitset&lt;2&gt;()
    3159. 

  3159. );
    3160. 

  3160. b(  // deduced arguments
    3161. 

  3161.     lvalue_bitset&lt;1&gt;()
    3162. 

  3162.   , lvalue_const_bitset&lt;0&gt;()
    3163. 

  3163. );
    3164. 

  3164. </pre>
    3165. 

  3165. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a>, <a class="reference external" href="../../test/preprocessor_deduced.cpp">preprocessor_deduced.cpp</a>, and
    3166. 

  3166. <a class="reference external" href="../../test/preprocessor_eval_cat_8.cpp">preprocessor_eval_cat_8.cpp</a> test programs demonstrate proper usage of this
    3167. 

  3167. macro.</p>
    3168. 

  3168. <p><strong>Macro parameters:</strong></p>
    3169. 

  3169. <ul class="simple">
    3170. 

  3170. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function call operator.</li>
    3171. 

  3171. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    3172. 

  3172. function call operator resides.</li>
    3173. 

  3173. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    3174. 

  3174. <em>argument-specifiers</em>, as defined below.</li>
    3175. 

  3175. </ul>
    3176. 

  3176. <p><strong>Argument specifiers syntax:</strong></p>
    3177. 

  3177. <pre class="literal-block">
    3178. 

  3178. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    3179. 

  3179. 

  3180. specifier-group0 ::= <em>specifier-group1</em> |
    3181. 

  3181.     (
    3182. 

  3182.         '<strong>(</strong>' '<strong>deduced</strong>'
    3183. 

  3183.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    3184. 

  3184.         '<strong>)</strong>'
    3185. 

  3185.     )
    3186. 

  3186. 

  3187. specifier-group1 ::=
    3188. 

  3188.     (
    3189. 

  3189.         '<strong>(</strong>' '<strong>optional</strong>'
    3190. 

  3190.             <em>optional-specifier</em> {<em>optional-specifier</em>}
    3191. 

  3191.         '<strong>)</strong>'
    3192. 

  3192.     ) | (
    3193. 

  3193.         '<strong>(</strong>' '<strong>required</strong>'
    3194. 

  3194.             <em>required-specifier</em> {<em>required-specifier</em>}
    3195. 

  3195.         '<strong>)</strong>'
    3196. 

  3196.     )
    3197. 

  3197. 

  3198. optional-specifier ::=
    3199. 

  3199.     '<strong>(</strong>'
    3200. 

  3200.         <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> '<strong>,</strong>' <em>default-value</em>
    3201. 

  3201.     ')'
    3202. 

  3202. 

  3203. required-specifier ::=
    3204. 

  3204.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    3205. 

  3205. 

  3206. restriction ::=
    3207. 

  3207.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    3208. 

  3208.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    3209. 

  3209.     '<strong>*</strong>'
    3210. 

  3210. </pre>
    3211. 

  3211. <ul class="simple">
    3212. 

  3212. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    3213. 

  3213. <li><tt class="docutils literal"><span class="pre">default-value</span></tt> is any valid C++ expression; if necessary, user code can
    3214. 

  3214. compute it in terms of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>, where <tt class="docutils literal"><span class="pre">previous-name</span></tt>
    3215. 

  3215. is the <tt class="docutils literal"><span class="pre">argument-name</span></tt> in a previous <tt class="docutils literal"><span class="pre">specifier-group0</span></tt> or
    3216. 

  3216. <tt class="docutils literal"><span class="pre">specifier-group1</span></tt>.  <em>This expression will be invoked exactly once.</em></li>
    3217. 

  3217. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    3218. 

  3218. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    3219. 

  3219. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    3220. 

  3220. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    3221. 

  3221. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    3222. 

  3222. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    3223. 

  3223. Metafunction Class</a> whose first argument will be the type of the
    3224. 

  3224. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    3225. 

  3225. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.  If
    3226. 

  3226. <tt class="docutils literal">restriction</tt> uses this form, then the type of the generated name
    3227. 

  3227. <tt class="docutils literal"><span class="pre">argument-name</span> ## _type</tt> will be computed in terms of the <strong>target
    3228. 

  3228. type</strong>, and the generated reference <tt class="docutils literal"><span class="pre">argument-name</span></tt> (but not its
    3229. 

  3229. corresponding entry in <tt class="docutils literal">args</tt>) will be cast to that type.</li>
    3230. 

  3230. </ul>
    3231. 

  3231. <p><strong>Approximate expansion:</strong></p>
    3232. 

  3232. <p>Where:</p>
    3233. 

  3233. <ul class="simple">
    3234. 

  3234. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    3235. 

  3235. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    3236. 

  3236. </ul>
    3237. 

  3237. <pre class="literal-block">
    3238. 

  3238. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    3239. 

  3239. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    3240. 

  3240. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    3241. 

  3241. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    3242. 

  3242. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    3243. 

  3243. template &lt;typename Args&gt;
    3244. 

  3244. using boost_param_result_const_ ## __LINE__ ## operator = <strong>result</strong>;
    3245. 

  3245. 

  3246. // If <strong>result</strong> is a simple return type:
    3247. 

  3247. template &lt;typename Args&gt;
    3248. 

  3248. struct boost_param_result_const_ ## __LINE__ ## operator
    3249. 

  3249. {
    3250. 

  3250.     typedef <strong>result</strong> type;
    3251. 

  3251. };
    3252. 

  3252. 

  3253. struct boost_param_params_const_ ## __LINE__ ## operator
    3254. 

  3254.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    3255. 

  3255.         <em>list of parameter specifications, based on arguments</em>
    3256. 

  3256.     &gt;
    3257. 

  3257. {
    3258. 

  3258. };
    3259. 

  3259. 

  3260. typedef boost_param_params_const_ ## __LINE__ ## operator
    3261. 

  3261.     boost_param_parameters_const_ ## __LINE__ ## operator;
    3262. 

  3262. 

  3263. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    3264. 

  3264. <strong>result</strong> operator()(
    3265. 

  3265.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    3266. 

  3266.   , typename boost_param_parameters_const_ ## __LINE__ ## operator
    3267. 

  3267.     ::match&lt;A0, …, A ## <strong>n</strong>&gt;::type
    3268. 

  3268.     = boost_param_parameters_const_ ## __LINE__ ## operator()
    3269. 

  3269. ) const
    3270. 

  3270. {
    3271. 

  3271.     return this-&gt;boost_param_impl_const ## __LINE__ ## operator(
    3272. 

  3272.         boost_param_parameters_const_ ## __LINE__ ## operator()(
    3273. 

  3273.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    3274. 

  3274.           , …
    3275. 

  3275.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    3276. 

  3276.         )
    3277. 

  3277.     );
    3278. 

  3278. }
    3279. 

  3279. 

  3280. <span class="vellipsis">⋮</span>
    3281. 

  3281. 

  3282. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    3283. 

  3283. <strong>result</strong> operator()(
    3284. 

  3284.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    3285. 

  3285.   , typename boost_param_parameters_const_ ## __LINE__ ## operator
    3286. 

  3286.     ::match&lt;A0, …, A ## <strong>m</strong>&gt;::type
    3287. 

  3287.     = boost_param_parameters_const_ ## __LINE__ ## operator()
    3288. 

  3288. ) const
    3289. 

  3289. {
    3290. 

  3290.     return this-&gt;boost_param_impl_const ## __LINE__ ## operator(
    3291. 

  3291.         boost_param_parameters_const_ ## __LINE__ ## operator()(
    3292. 

  3292.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    3293. 

  3293.           , …
    3294. 

  3294.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    3295. 

  3295.         )
    3296. 

  3296.     );
    3297. 

  3297. }
    3298. 

  3298. 

  3299. template &lt;typename Args&gt;
    3300. 

  3300. typename boost_param_result_const_ ## __LINE__ ## operator&lt;Args&gt;::type
    3301. 

  3301.     boost_param_impl_const ## __LINE__ ## operator(Args const&amp; args) const
    3302. 

  3302. {
    3303. 

  3303.     return this-&gt;
    3304. 

  3304.     boost_param_dispatch_const_0boost_ ## __LINE__ ## operator(
    3305. 

  3305.         static_cast&lt;
    3306. 

  3306.             typename boost_param_result_const_ ## __LINE__ ## operator&lt;
    3307. 

  3307.                 Args
    3308. 

  3308.             &gt;::type(*)()
    3309. 

  3309.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    3310. 

  3310.       , args
    3311. 

  3311.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    3312. 

  3312.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    3313. 

  3313.                 Args
    3314. 

  3314.               , <em>keyword tag type of required parameter</em> ## <strong>0</strong>
    3315. 

  3315.             &gt;::type
    3316. 

  3316.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>0</strong>])
    3317. 

  3317.       , …
    3318. 

  3318.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    3319. 

  3319.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    3320. 

  3320.                 Args
    3321. 

  3321.               , <em>keyword tag type of required parameter</em> ## <strong>n</strong>
    3322. 

  3322.             &gt;::type
    3323. 

  3323.         &gt;(args[ <em>keyword object of required parameter</em> ## <strong>n</strong>])
    3324. 

  3324.     );
    3325. 

  3325. }
    3326. 

  3326. 

  3327. template &lt;
    3328. 

  3328.     typename ResultType
    3329. 

  3329.   , typename Args
    3330. 

  3330.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    3331. 

  3331.   , …
    3332. 

  3332.   , typename <em>argument name</em> ## <strong>n</strong> ## _type
    3333. 

  3333. &gt;
    3334. 

  3334. ResultType
    3335. 

  3335.     boost_param_dispatch_const_0boost_ ## __LINE__ ## operator(
    3336. 

  3336.         (ResultType(*)())
    3337. 

  3337.       , Args const&amp; args
    3338. 

  3338.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    3339. 

  3339.       , …
    3340. 

  3340.       , <em>argument name</em> ## <strong>n</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>n</strong>
    3341. 

  3341.     ) const
    3342. 

  3342. {
    3343. 

  3343.     return this-&gt;
    3344. 

  3344.     boost_param_dispatch_const_0boost_ ## __LINE__ ## operator(
    3345. 

  3345.         static_cast&lt;ResultType(*)()&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    3346. 

  3346.       , (args, <em>keyword object of optional parameter</em> ## <strong>n + 1</strong> =
    3347. 

  3347.             <em>default value of optional parameter</em> ## <strong>n + 1</strong>
    3348. 

  3348.         )
    3349. 

  3349.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>0</strong> ## _type&gt;(
    3350. 

  3350.             <em>argument name</em> ## <strong>0</strong>
    3351. 

  3351.         )
    3352. 

  3352.       , …
    3353. 

  3353.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;<em>argument name</em> ## <strong>n</strong> ## _type&gt;(
    3354. 

  3354.             <em>argument name</em> ## <strong>n</strong>
    3355. 

  3355.         )
    3356. 

  3356.       , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;
    3357. 

  3357.             typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;
    3358. 

  3358.                 Args
    3359. 

  3359.               , <em>keyword tag type of optional parameter</em> ## <strong>n + 1</strong>
    3360. 

  3360.             &gt;::type
    3361. 

  3361.         &gt;(<em>default value of optional parameter</em> ## <strong>n + 1</strong>)
    3362. 

  3362.     );
    3363. 

  3363. }
    3364. 

  3364. 

  3365. <span class="vellipsis">⋮</span>
    3366. 

  3366. 

  3367. template &lt;
    3368. 

  3368.     typename ResultType
    3369. 

  3369.   , typename Args
    3370. 

  3370.   , typename <em>argument name</em> ## <strong>0</strong> ## _type
    3371. 

  3371.   , …
    3372. 

  3372.   , typename <em>argument name</em> ## <strong>m</strong> ## _type
    3373. 

  3373. &gt;
    3374. 

  3374. ResultType
    3375. 

  3375.     boost_param_dispatch_const_0boost_ ## __LINE__ ## operator(
    3376. 

  3376.         (ResultType(*)())
    3377. 

  3377.       , Args const&amp; args
    3378. 

  3378.       , <em>argument name</em> ## <strong>0</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>0</strong>
    3379. 

  3379.       , …
    3380. 

  3380.       , <em>argument name</em> ## <strong>m</strong> ## _type&amp;&amp; <em>argument name</em> ## <strong>m</strong>
    3381. 

  3381.     ) const
    3382. 

  3382. </pre>
    3383. 

  3383. </div>
    3384. 

  3384. <div class="section" id="boost-parameter-constructor-cls-impl-tag-namespace-arguments">
    3385. 

  3385. <span id="boost-parameter-constructor"></span><h2><a class="toc-backref" href="#id62">7.6&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_CONSTRUCTOR(cls, impl, tag_namespace, arguments)</tt></a></h2>
    3386. 

  3386. <table class="docutils field-list" frame="void" rules="none">
    3387. 

  3387. <col class="field-name" />
    3388. 

  3388. <col class="field-body" />
    3389. 

  3389. <tbody valign="top">
    3390. 

  3390. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    3391. 

  3391. </tr>
    3392. 

  3392. </tbody>
    3393. 

  3393. </table>
    3394. 

  3394. <p>Generates a constructor that can take in positional arguments, composed
    3395. 

  3395. arguments, named arguments, and deduced arguments.</p>
    3396. 

  3396. <table class="docutils field-list" frame="void" rules="none">
    3397. 

  3397. <col class="field-name" />
    3398. 

  3398. <col class="field-body" />
    3399. 

  3399. <tbody valign="top">
    3400. 

  3400. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    3401. 

  3401. </tr>
    3402. 

  3402. </tbody>
    3403. 

  3403. </table>
    3404. 

  3404. <p>Define the named parameters that will comprise the argument specification that
    3405. 

  3405. this macro will use.  Ensure that all their tag types are in the same
    3406. 

  3406. namespace, which is <tt class="docutils literal">tag</tt> by default.</p>
    3407. 

  3407. <pre class="literal-block">
    3408. 

  3408. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(y)
    3409. 

  3409. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(z)
    3410. 

  3410. </pre>
    3411. 

  3411. <p>In the base class, implement a delegate constructor template that takes in an
    3412. 

  3412. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>.  You must pass the identifiers with leading underscores to
    3413. 

  3413. <tt class="docutils literal">args</tt> in order to extract the corresponding arguments.</p>
    3414. 

  3414. <pre class="literal-block">
    3415. 

  3415. class char_read_base
    3416. 

  3416. {
    3417. 

  3417.     int index;
    3418. 

  3418.     char const* key;
    3419. 

  3419. 

  3420.  public:
    3421. 

  3421.     template &lt;typename Args&gt;
    3422. 

  3422.     explicit char_read_base(Args const&amp; args)
    3423. 

  3423.       : index(args[_y]), key(args[_z])
    3424. 

  3424.     {
    3425. 

  3425.     }
    3426. 

  3426. 

  3427.     <a class="reference internal" href="#boost-parameter-const-function-call-operator"><tt class="docutils literal">BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR</tt></a>((char), tag,
    3428. 

  3428.         (deduced
    3429. 

  3429.             (required
    3430. 

  3430.                 (y, (bool))
    3431. 

  3431.                 (z, (<a class="reference external" href="http://en.cppreference.com/w/cpp/container/map">std::map</a>&lt;char const*, <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>&gt;))
    3432. 

  3432.             )
    3433. 

  3433.         )
    3434. 

  3434.     )
    3435. 

  3435.     {
    3436. 

  3436.         return y ? (
    3437. 

  3437.             (z.find(this-&gt;key)-&gt;second)[this-&gt;index]
    3438. 

  3438.         ) : this-&gt;key[this-&gt;index];
    3439. 

  3439.     }
    3440. 

  3440. };
    3441. 

  3441. </pre>
    3442. 

  3442. <p>Use the macro as a substitute for a normal constructor definition.  Note the
    3443. 

  3443. lack of an explicit body.  Enclose the base type in parentheses.  For each
    3444. 

  3444. parameter, also enclose the expected value type in parentheses.  Since the
    3445. 

  3445. value types are mutually exclusive, you can wrap the parameters in a
    3446. 

  3446. <tt class="docutils literal">(deduced …)</tt> clause.</p>
    3447. 

  3447. <pre class="literal-block">
    3448. 

  3448. struct char_reader : public char_read_base
    3449. 

  3449. {
    3450. 

  3450.     BOOST_PARAMETER_CONSTRUCTOR(char_reader, (char_read_base), tag,
    3451. 

  3451.         (deduced
    3452. 

  3452.             (required
    3453. 

  3453.                 (y, (int))
    3454. 

  3454.                 (z, (char const*))
    3455. 

  3455.             )
    3456. 

  3456.         )
    3457. 

  3457.     )
    3458. 

  3458. };
    3459. 

  3459. </pre>
    3460. 

  3460. <p>The following <tt class="docutils literal">char_reader</tt> constructor calls are legal.</p>
    3461. 

  3461. <pre class="literal-block">
    3462. 

  3462. char const* keys[] = {&quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;};
    3463. 

  3463. <a class="reference external" href="http://en.cppreference.com/w/cpp/container/map">std::map</a>&lt;char const*, <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>&gt; k2s;
    3464. 

  3464. k2s[keys[0]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;qux&quot;);
    3465. 

  3465. k2s[keys[1]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;wmb&quot;);
    3466. 

  3466. k2s[keys[2]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;zxc&quot;);
    3467. 

  3467. 

  3468. // positional arguments
    3469. 

  3469. char_reader r0(0, keys[0]);
    3470. 

  3470. BOOST_TEST_EQ('q', (r0(true, k2s)));
    3471. 

  3471. BOOST_TEST_EQ('f', (r0(false, k2s)));
    3472. 

  3472. 

  3473. // named arguments
    3474. 

  3474. char_reader r1(_z = keys[1], _y = 1);
    3475. 

  3475. BOOST_TEST_EQ('m', (r1(_z = k2s, _y = true)));
    3476. 

  3476. BOOST_TEST_EQ('a', (r1(_z = k2s, _y = false)));
    3477. 

  3477. 

  3478. // deduced arguments
    3479. 

  3479. char_reader r2(keys[2], 2);
    3480. 

  3480. BOOST_TEST_EQ('c', (r2(k2s, true)));
    3481. 

  3481. BOOST_TEST_EQ('z', (r2(k2s, false)));
    3482. 

  3482. </pre>
    3483. 

  3483. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> and <a class="reference external" href="../../test/preprocessor_deduced.cpp">preprocessor_deduced.cpp</a> test programs
    3484. 

  3484. demonstrate proper usage of this macro.</p>
    3485. 

  3485. <p><strong>Macro parameters:</strong></p>
    3486. 

  3486. <ul class="simple">
    3487. 

  3487. <li><tt class="docutils literal">cls</tt> is the name of the enclosing class.</li>
    3488. 

  3488. <li><tt class="docutils literal">impl</tt> is the parenthesized implementation base class for <tt class="docutils literal">cls</tt>.</li>
    3489. 

  3489. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    3490. 

  3490. constructor resides.</li>
    3491. 

  3491. <li><tt class="docutils literal">arguments</tt> is a list of <em>argument-specifiers</em>, as defined below.</li>
    3492. 

  3492. </ul>
    3493. 

  3493. <p><strong>Argument specifiers syntax:</strong></p>
    3494. 

  3494. <pre class="literal-block">
    3495. 

  3495. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    3496. 

  3496. 

  3497. specifier-group0 ::= <em>specifier-group1</em> |
    3498. 

  3498.     (
    3499. 

  3499.         '<strong>(</strong>' '<strong>deduced</strong>'
    3500. 

  3500.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    3501. 

  3501.         '<strong>)</strong>'
    3502. 

  3502.     )
    3503. 

  3503. 

  3504. specifier-group1 ::=
    3505. 

  3505.     (
    3506. 

  3506.         '<strong>(</strong>' '<strong>optional</strong>'
    3507. 

  3507.             <em>specifier</em> {<em>specifier</em>}
    3508. 

  3508.         '<strong>)</strong>'
    3509. 

  3509.     ) | (
    3510. 

  3510.         '<strong>(</strong>' '<strong>required</strong>'
    3511. 

  3511.             <em>specifier</em> {<em>specifier</em>}
    3512. 

  3512.         '<strong>)</strong>'
    3513. 

  3513.     )
    3514. 

  3514. 

  3515. specifier ::=
    3516. 

  3516.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    3517. 

  3517. 

  3518. restriction ::=
    3519. 

  3519.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    3520. 

  3520.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    3521. 

  3521.     '<strong>*</strong>'
    3522. 

  3522. </pre>
    3523. 

  3523. <ul class="simple">
    3524. 

  3524. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    3525. 

  3525. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    3526. 

  3526. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    3527. 

  3527. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    3528. 

  3528. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    3529. 

  3529. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    3530. 

  3530. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    3531. 

  3531. Metafunction Class</a> whose first argument will be the type of the
    3532. 

  3532. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    3533. 

  3533. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.</li>
    3534. 

  3534. </ul>
    3535. 

  3535. <p>Note that <em>specifier</em> does not include <em>default-value</em>.  It is up to the
    3536. 

  3536. delegate constructor in <tt class="docutils literal">impl</tt> to determine the default value of all
    3537. 

  3537. optional arguments.</p>
    3538. 

  3538. <p><strong>Approximate expansion:</strong></p>
    3539. 

  3539. <p>Where:</p>
    3540. 

  3540. <ul class="simple">
    3541. 

  3541. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    3542. 

  3542. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    3543. 

  3543. </ul>
    3544. 

  3544. <pre class="literal-block">
    3545. 

  3545. struct boost_param_params_ ## __LINE__ ## ctor
    3546. 

  3546.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    3547. 

  3547.         <em>list of parameter specifications, based on arguments</em>
    3548. 

  3548.     &gt;
    3549. 

  3549. {
    3550. 

  3550. };
    3551. 

  3551. 

  3552. typedef boost_param_params_ ## __LINE__ ## ctor
    3553. 

  3553.     constructor_parameters ## __LINE__;
    3554. 

  3554. 

  3555. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    3556. 

  3556. <strong>cls</strong>(A0&amp;&amp; a0, …, A ## <strong>n</strong> &amp;&amp; a ## <strong>n</strong>)
    3557. 

  3557.   : <strong>impl</strong>(
    3558. 

  3558.         constructor_parameters ## __LINE__(
    3559. 

  3559.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    3560. 

  3560.           , …
    3561. 

  3561.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    3562. 

  3562.         )
    3563. 

  3563.     )
    3564. 

  3564. {
    3565. 

  3565. }
    3566. 

  3566. 

  3567. <span class="vellipsis">⋮</span>
    3568. 

  3568. 

  3569. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    3570. 

  3570. <strong>cls</strong>(A0&amp;&amp; a0, …, A ## <strong>m</strong> &amp;&amp; a ## <strong>m</strong>)
    3571. 

  3571.   : <strong>impl</strong>(
    3572. 

  3572.         constructor_parameters ## __LINE__(
    3573. 

  3573.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    3574. 

  3574.           , …
    3575. 

  3575.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    3576. 

  3576.         )
    3577. 

  3577.     )
    3578. 

  3578. {
    3579. 

  3579. }
    3580. 

  3580. </pre>
    3581. 

  3581. </div>
    3582. 

  3582. <div class="section" id="boost-parameter-basic-function-result-name-tag-namespace-arguments">
    3583. 

  3583. <span id="boost-parameter-basic-function"></span><h2><a class="toc-backref" href="#id63">7.7&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_FUNCTION(result, name, tag_namespace, arguments)</tt></a></h2>
    3584. 

  3584. <table class="docutils field-list" frame="void" rules="none">
    3585. 

  3585. <col class="field-name" />
    3586. 

  3586. <col class="field-body" />
    3587. 

  3587. <tbody valign="top">
    3588. 

  3588. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    3589. 

  3589. </tr>
    3590. 

  3590. </tbody>
    3591. 

  3591. </table>
    3592. 

  3592. <p>Generates a function that can take in positional arguments, composed
    3593. 

  3593. arguments, named arguments, and deduced arguments.</p>
    3594. 

  3594. <table class="docutils field-list" frame="void" rules="none">
    3595. 

  3595. <col class="field-name" />
    3596. 

  3596. <col class="field-body" />
    3597. 

  3597. <tbody valign="top">
    3598. 

  3598. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    3599. 

  3599. </tr>
    3600. 

  3600. </tbody>
    3601. 

  3601. </table>
    3602. 

  3602. <p>The return type of each of the following function templates falls under a
    3603. 

  3603. different value category.</p>
    3604. 

  3604. <pre class="literal-block">
    3605. 

  3605. template &lt;std::size_t N&gt;
    3606. 

  3606. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    3607. 

  3607. {
    3608. 

  3608.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3609. 

  3609. }
    3610. 

  3610. 

  3611. template &lt;std::size_t N&gt;
    3612. 

  3612. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    3613. 

  3613. {
    3614. 

  3614.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3615. 

  3615. }
    3616. 

  3616. 

  3617. template &lt;std::size_t N&gt;
    3618. 

  3618. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    3619. 

  3619. {
    3620. 

  3620.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3621. 

  3621.     return lset;
    3622. 

  3622. }
    3623. 

  3623. 

  3624. template &lt;std::size_t N&gt;
    3625. 

  3625. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    3626. 

  3626. {
    3627. 

  3627.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3628. 

  3628.     return clset;
    3629. 

  3629. }
    3630. 

  3630. </pre>
    3631. 

  3631. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    3632. 

  3632. to return the correct value category when passed in an object returned by one
    3633. 

  3633. of the functions defined above.  Assume that
    3634. 

  3634. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    3635. 

  3635. <pre class="literal-block">
    3636. 

  3636. enum invoked
    3637. 

  3637. {
    3638. 

  3638.     passed_by_lvalue_reference_to_const
    3639. 

  3639.   , passed_by_lvalue_reference
    3640. 

  3640.   , passed_by_rvalue_reference_to_const
    3641. 

  3641.   , passed_by_rvalue_reference
    3642. 

  3642. };
    3643. 

  3643. 

  3644. struct U
    3645. 

  3645. {
    3646. 

  3646.     template &lt;std::size_t N&gt;
    3647. 

  3647.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    3648. 

  3648.     {
    3649. 

  3649.         return passed_by_lvalue_reference_to_const;
    3650. 

  3650.     }
    3651. 

  3651. 

  3652.     template &lt;std::size_t N&gt;
    3653. 

  3653.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    3654. 

  3654.     {
    3655. 

  3655.         return passed_by_lvalue_reference;
    3656. 

  3656.     }
    3657. 

  3657. 

  3658.     template &lt;std::size_t N&gt;
    3659. 

  3659.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    3660. 

  3660.     {
    3661. 

  3661.         return passed_by_rvalue_reference_to_const;
    3662. 

  3662.     }
    3663. 

  3663. 

  3664.     template &lt;std::size_t N&gt;
    3665. 

  3665.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    3666. 

  3666.     {
    3667. 

  3667.         return passed_by_rvalue_reference;
    3668. 

  3668.     }
    3669. 

  3669. };
    3670. 

  3670. </pre>
    3671. 

  3671. <p>Define the named parameters that will comprise the argument specification that
    3672. 

  3672. this macro will use.  Ensure that all their tag types are in the same
    3673. 

  3673. namespace, which is <tt class="docutils literal">kw</tt> in this case.  The identifiers with leading
    3674. 

  3674. underscores can be passed to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    3675. 

  3675. same argument to which the corresponding named parameter (without underscores)
    3676. 

  3676. is bound, as will be shown later.</p>
    3677. 

  3677. <pre class="literal-block">
    3678. 

  3678. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw) in(lrc))
    3679. 

  3679. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw) in_out(lr))
    3680. 

  3680. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw) in(rrc))
    3681. 

  3681. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw) consume(rr))
    3682. 

  3682. </pre>
    3683. 

  3683. <p>Use the macro as a substitute for a normal function header.  Enclose the
    3684. 

  3684. return type <tt class="docutils literal">bool</tt> in parentheses.  For each parameter, also enclose the
    3685. 

  3685. expected value type in parentheses.  Since the value types are mutually
    3686. 

  3686. exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    3687. 

  3687. clause.  Otherwise, just as with a normal function, the order in which you
    3688. 

  3688. specify the parameters determines their position.  However, unlike a normal
    3689. 

  3689. function, default values must be specified within the function body.  Also
    3690. 

  3690. within the function body, you must pass the matching identifier with the
    3691. 

  3691. leading underscore to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    3692. 

  3692. corresponding argument, but at least this doesn't require <tt class="docutils literal"><span class="pre">std::forward</span></tt> to
    3693. 

  3693. preserve value categories.</p>
    3694. 

  3694. <pre class="literal-block">
    3695. 

  3695. BOOST_PARAMETER_BASIC_FUNCTION((bool), evaluate, kw,
    3696. 

  3696.     (deduced
    3697. 

  3697.         (required
    3698. 

  3698.             (lrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;1&gt;))
    3699. 

  3699.             (lr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;2&gt;))
    3700. 

  3700.         )
    3701. 

  3701.         (optional
    3702. 

  3702.             (rrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;3&gt;))
    3703. 

  3703.             (rr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;4&gt;))
    3704. 

  3704.         )
    3705. 

  3705.     )
    3706. 

  3706. )
    3707. 

  3707. {
    3708. 

  3708.     BOOST_TEST_EQ(
    3709. 

  3709.         passed_by_lvalue_reference_to_const
    3710. 

  3710.       , U::evaluate_category&lt;0&gt;(args[_lrc])
    3711. 

  3711.     );
    3712. 

  3712.     BOOST_TEST_EQ(
    3713. 

  3713.         passed_by_lvalue_reference
    3714. 

  3714.       , U::evaluate_category&lt;1&gt;(args[_lr])
    3715. 

  3715.     );
    3716. 

  3716.     BOOST_TEST_EQ(
    3717. 

  3717.         passed_by_rvalue_reference_to_const
    3718. 

  3718.       , U::evaluate_category&lt;2&gt;(
    3719. 

  3719.             args[_rrc0 | rvalue_const_bitset&lt;2&gt;()]
    3720. 

  3720.         )
    3721. 

  3721.     );
    3722. 

  3722.     BOOST_TEST_EQ(
    3723. 

  3723.         passed_by_rvalue_reference
    3724. 

  3724.       , U::evaluate_category&lt;3&gt;(args[_rr0 | rvalue_bitset&lt;3&gt;()])
    3725. 

  3725.     );
    3726. 

  3726. 

  3727.     return true;
    3728. 

  3728. }
    3729. 

  3729. </pre>
    3730. 

  3730. <p>The following function calls are legal.</p>
    3731. 

  3731. <pre class="literal-block">
    3732. 

  3732. evaluate(  // positional arguments
    3733. 

  3733.     lvalue_const_bitset&lt;0&gt;()
    3734. 

  3734.   , lvalue_bitset&lt;1&gt;()
    3735. 

  3735.   , rvalue_const_bitset&lt;2&gt;()
    3736. 

  3736.   , rvalue_bitset&lt;3&gt;()
    3737. 

  3737. );
    3738. 

  3738. evaluate(  // positional arguments
    3739. 

  3739.     lvalue_const_bitset&lt;0&gt;()
    3740. 

  3740.   , lvalue_bitset&lt;1&gt;()
    3741. 

  3741. );
    3742. 

  3742. evaluate((  // composed arguments
    3743. 

  3743.     _rr0 = rvalue_bitset&lt;3&gt;()
    3744. 

  3744.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    3745. 

  3745.   , _lr0 = lvalue_bitset&lt;1&gt;()
    3746. 

  3746.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    3747. 

  3747. ));
    3748. 

  3748. evaluate(  // named arguments
    3749. 

  3749.     _rr0 = rvalue_bitset&lt;3&gt;()
    3750. 

  3750.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    3751. 

  3751.   , _lr0 = lvalue_bitset&lt;1&gt;()
    3752. 

  3752.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    3753. 

  3753. );
    3754. 

  3754. evaluate(  // named arguments
    3755. 

  3755.     _lr0 = lvalue_bitset&lt;1&gt;()
    3756. 

  3756.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    3757. 

  3757. );
    3758. 

  3758. </pre>
    3759. 

  3759. <p>Because the parameters were wrapped in a <tt class="docutils literal">(deduced …)</tt> clause, the following
    3760. 

  3760. function calls are also legal.</p>
    3761. 

  3761. <pre class="literal-block">
    3762. 

  3762. evaluate(  // deduced arguments
    3763. 

  3763.     rvalue_bitset&lt;3&gt;()
    3764. 

  3764.   , lvalue_const_bitset&lt;0&gt;()
    3765. 

  3765.   , lvalue_bitset&lt;1&gt;()
    3766. 

  3766.   , rvalue_const_bitset&lt;2&gt;()
    3767. 

  3767. );
    3768. 

  3768. evaluate(  // deduced arguments
    3769. 

  3769.     lvalue_bitset&lt;1&gt;()
    3770. 

  3770.   , lvalue_const_bitset&lt;0&gt;()
    3771. 

  3771. );
    3772. 

  3772. </pre>
    3773. 

  3773. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> test program demonstrates proper usage of this macro.</p>
    3774. 

  3774. <p><strong>Macro parameters:</strong></p>
    3775. 

  3775. <ul class="simple">
    3776. 

  3776. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    3777. 

  3777. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    3778. 

  3778. generated forwarding functions.</li>
    3779. 

  3779. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    3780. 

  3780. function resides.</li>
    3781. 

  3781. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    3782. 

  3782. <em>argument-specifiers</em>, as defined below.</li>
    3783. 

  3783. </ul>
    3784. 

  3784. <p><strong>Argument specifiers syntax:</strong></p>
    3785. 

  3785. <pre class="literal-block">
    3786. 

  3786. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    3787. 

  3787. 

  3788. specifier-group0 ::= <em>specifier-group1</em> |
    3789. 

  3789.     (
    3790. 

  3790.         '<strong>(</strong>' '<strong>deduced</strong>'
    3791. 

  3791.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    3792. 

  3792.         '<strong>)</strong>'
    3793. 

  3793.     )
    3794. 

  3794. 

  3795. specifier-group1 ::=
    3796. 

  3796.     (
    3797. 

  3797.         '<strong>(</strong>' '<strong>optional</strong>'
    3798. 

  3798.             <em>specifier</em> {<em>specifier</em>}
    3799. 

  3799.         '<strong>)</strong>'
    3800. 

  3800.     ) | (
    3801. 

  3801.         '<strong>(</strong>' '<strong>required</strong>'
    3802. 

  3802.             <em>specifier</em> {<em>specifier</em>}
    3803. 

  3803.         '<strong>)</strong>'
    3804. 

  3804.     )
    3805. 

  3805. 

  3806. specifier ::=
    3807. 

  3807.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    3808. 

  3808. 

  3809. restriction ::=
    3810. 

  3810.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    3811. 

  3811.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    3812. 

  3812.     '<strong>*</strong>'
    3813. 

  3813. </pre>
    3814. 

  3814. <ul class="simple">
    3815. 

  3815. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    3816. 

  3816. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    3817. 

  3817. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    3818. 

  3818. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    3819. 

  3819. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    3820. 

  3820. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    3821. 

  3821. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    3822. 

  3822. Metafunction Class</a> whose first argument will be the type of the
    3823. 

  3823. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    3824. 

  3824. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.</li>
    3825. 

  3825. </ul>
    3826. 

  3826. <p>Note that <em>specifier</em> does not include <em>default-value</em>.  It is up to the
    3827. 

  3827. function body to determine the default value of all optional arguments.</p>
    3828. 

  3828. <p><strong>Approximate expansion:</strong></p>
    3829. 

  3829. <p>Where:</p>
    3830. 

  3830. <ul class="simple">
    3831. 

  3831. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    3832. 

  3832. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    3833. 

  3833. </ul>
    3834. 

  3834. <pre class="literal-block">
    3835. 

  3835. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    3836. 

  3836. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    3837. 

  3837. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    3838. 

  3838. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    3839. 

  3839. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    3840. 

  3840. template &lt;typename Args&gt;
    3841. 

  3841. using boost_param_result_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    3842. 

  3842. 

  3843. // If <strong>result</strong> is a simple return type:
    3844. 

  3844. template &lt;typename Args&gt;
    3845. 

  3845. struct boost_param_result_ ## __LINE__ ## <strong>name</strong>
    3846. 

  3846. {
    3847. 

  3847.     typedef <strong>result</strong> type;
    3848. 

  3848. };
    3849. 

  3849. 

  3850. struct boost_param_params_ ## __LINE__ ## <strong>name</strong>
    3851. 

  3851.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    3852. 

  3852.         <em>list of parameter specifications, based on arguments</em>
    3853. 

  3853.     &gt;
    3854. 

  3854. {
    3855. 

  3855. };
    3856. 

  3856. 

  3857. typedef boost_param_params_ ## __LINE__ ## <strong>name</strong>
    3858. 

  3858.     boost_param_parameters_ ## __LINE__ ## <strong>name</strong>;
    3859. 

  3859. 

  3860. template &lt;typename Args&gt;
    3861. 

  3861. typename boost_param_result_ ## __LINE__ ## <strong>name</strong>&lt;Args&gt;::type
    3862. 

  3862.     boost_param_impl ## <strong>name</strong>(Args const&amp;);
    3863. 

  3863. 

  3864. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    3865. 

  3865. <strong>result</strong> <strong>name</strong>(
    3866. 

  3866.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    3867. 

  3867.   , typename boost_param_parameters_ ## __LINE__ ## <strong>name</strong>
    3868. 

  3868.     ::match&lt;A0, …, A ## <strong>n</strong>&gt;::type
    3869. 

  3869.     = boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()
    3870. 

  3870. )
    3871. 

  3871. {
    3872. 

  3872.     return boost_param_impl ## __LINE__ ## <strong>name</strong>(
    3873. 

  3873.         boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()(
    3874. 

  3874.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    3875. 

  3875.           , …
    3876. 

  3876.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    3877. 

  3877.         )
    3878. 

  3878.     );
    3879. 

  3879. }
    3880. 

  3880. 

  3881. <span class="vellipsis">⋮</span>
    3882. 

  3882. 

  3883. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    3884. 

  3884. <strong>result</strong> <strong>name</strong>(
    3885. 

  3885.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    3886. 

  3886.   , typename boost_param_parameters_ ## __LINE__ ## <strong>name</strong>
    3887. 

  3887.     ::match&lt;A0, …, A ## <strong>m</strong>&gt;::type
    3888. 

  3888.     = boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()
    3889. 

  3889. )
    3890. 

  3890. {
    3891. 

  3891.     return boost_param_impl ## __LINE__ ## <strong>name</strong>(
    3892. 

  3892.         boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()(
    3893. 

  3893.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    3894. 

  3894.           , …
    3895. 

  3895.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    3896. 

  3896.         )
    3897. 

  3897.     );
    3898. 

  3898. }
    3899. 

  3899. 

  3900. template &lt;typename Args&gt;
    3901. 

  3901. typename boost_param_result_ ## __LINE__ ## <strong>name</strong>&lt;Args&gt;::type
    3902. 

  3902.     boost_param_impl ## __LINE__ ## <strong>name</strong>(Args const&amp; args)
    3903. 

  3903. </pre>
    3904. 

  3904. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    3905. 

  3905. available for use within the function body.</p>
    3906. 

  3906. </div>
    3907. 

  3907. <div class="section" id="boost-parameter-basic-member-function-result-name-tag-ns-arguments">
    3908. 

  3908. <span id="boost-parameter-basic-member-function"></span><h2><a class="toc-backref" href="#id64">7.8&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_MEMBER_FUNCTION(result, name, tag_ns, arguments)</tt></a></h2>
    3909. 

  3909. <table class="docutils field-list" frame="void" rules="none">
    3910. 

  3910. <col class="field-name" />
    3911. 

  3911. <col class="field-body" />
    3912. 

  3912. <tbody valign="top">
    3913. 

  3913. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    3914. 

  3914. </tr>
    3915. 

  3915. </tbody>
    3916. 

  3916. </table>
    3917. 

  3917. <p>Generates a member function that can take in positional arguments, composed
    3918. 

  3918. arguments, named arguments, and deduced arguments.</p>
    3919. 

  3919. <table class="docutils field-list" frame="void" rules="none">
    3920. 

  3920. <col class="field-name" />
    3921. 

  3921. <col class="field-body" />
    3922. 

  3922. <tbody valign="top">
    3923. 

  3923. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    3924. 

  3924. </tr>
    3925. 

  3925. </tbody>
    3926. 

  3926. </table>
    3927. 

  3927. <p>The return type of each of the following function templates falls under a
    3928. 

  3928. different value category.</p>
    3929. 

  3929. <pre class="literal-block">
    3930. 

  3930. template &lt;std::size_t N&gt;
    3931. 

  3931. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    3932. 

  3932. {
    3933. 

  3933.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3934. 

  3934. }
    3935. 

  3935. 

  3936. template &lt;std::size_t N&gt;
    3937. 

  3937. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    3938. 

  3938. {
    3939. 

  3939.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3940. 

  3940. }
    3941. 

  3941. 

  3942. template &lt;std::size_t N&gt;
    3943. 

  3943. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    3944. 

  3944. {
    3945. 

  3945.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3946. 

  3946.     return lset;
    3947. 

  3947. }
    3948. 

  3948. 

  3949. template &lt;std::size_t N&gt;
    3950. 

  3950. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    3951. 

  3951. {
    3952. 

  3952.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    3953. 

  3953.     return clset;
    3954. 

  3954. }
    3955. 

  3955. </pre>
    3956. 

  3956. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    3957. 

  3957. to return the correct value category when passed in an object returned by one
    3958. 

  3958. of the functions defined above.  Assume that
    3959. 

  3959. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    3960. 

  3960. <pre class="literal-block">
    3961. 

  3961. enum invoked
    3962. 

  3962. {
    3963. 

  3963.     passed_by_lvalue_reference_to_const
    3964. 

  3964.   , passed_by_lvalue_reference
    3965. 

  3965.   , passed_by_rvalue_reference_to_const
    3966. 

  3966.   , passed_by_rvalue_reference
    3967. 

  3967. };
    3968. 

  3968. 

  3969. struct U
    3970. 

  3970. {
    3971. 

  3971.     template &lt;std::size_t N&gt;
    3972. 

  3972.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    3973. 

  3973.     {
    3974. 

  3974.         return passed_by_lvalue_reference_to_const;
    3975. 

  3975.     }
    3976. 

  3976. 

  3977.     template &lt;std::size_t N&gt;
    3978. 

  3978.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    3979. 

  3979.     {
    3980. 

  3980.         return passed_by_lvalue_reference;
    3981. 

  3981.     }
    3982. 

  3982. 

  3983.     template &lt;std::size_t N&gt;
    3984. 

  3984.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    3985. 

  3985.     {
    3986. 

  3986.         return passed_by_rvalue_reference_to_const;
    3987. 

  3987.     }
    3988. 

  3988. 

  3989.     template &lt;std::size_t N&gt;
    3990. 

  3990.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    3991. 

  3991.     {
    3992. 

  3992.         return passed_by_rvalue_reference;
    3993. 

  3993.     }
    3994. 

  3994. };
    3995. 

  3995. </pre>
    3996. 

  3996. <p>Define the named parameters that will comprise the argument specification that
    3997. 

  3997. this macro will use.  Ensure that all their tag types are in the same
    3998. 

  3998. namespace, which is <tt class="docutils literal">kw</tt> in this case.  The identifiers with leading
    3999. 

  3999. underscores can be passed to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    4000. 

  4000. same argument to which the corresponding named parameter (without underscores)
    4001. 

  4001. is bound, as will be shown later.</p>
    4002. 

  4002. <pre class="literal-block">
    4003. 

  4003. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw) in(lrc))
    4004. 

  4004. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw) in_out(lr))
    4005. 

  4005. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw) in(rrc))
    4006. 

  4006. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw) consume(rr))
    4007. 

  4007. </pre>
    4008. 

  4008. <p>Use the macro as a substitute for a normal <tt class="docutils literal">static</tt> member function
    4009. 

  4009. header.  Enclose the return type <tt class="docutils literal">bool</tt> in parentheses.  For each parameter,
    4010. 

  4010. also enclose the expected value type in parentheses.  Since the value types
    4011. 

  4011. are mutually exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    4012. 

  4012. clause.  Otherwise, just as with a normal function, the order in which you
    4013. 

  4013. specify the parameters determines their position.  However, unlike a normal
    4014. 

  4014. function, default values must be specified within the function body.  Also
    4015. 

  4015. within the function body, you must pass the matching identifier with the
    4016. 

  4016. leading underscore to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    4017. 

  4017. corresponding argument, but at least this doesn't require <tt class="docutils literal"><span class="pre">std::forward</span></tt> to
    4018. 

  4018. preserve value categories.</p>
    4019. 

  4019. <pre class="literal-block">
    4020. 

  4020. struct B
    4021. 

  4021. {
    4022. 

  4022.     BOOST_PARAMETER_BASIC_MEMBER_FUNCTION((bool), static evaluate, kw,
    4023. 

  4023.         (deduced
    4024. 

  4024.             (required
    4025. 

  4025.                 (lrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;1&gt;))
    4026. 

  4026.                 (lr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;2&gt;))
    4027. 

  4027.             )
    4028. 

  4028.             (optional
    4029. 

  4029.                 (rrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;3&gt;))
    4030. 

  4030.                 (rr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;4&gt;))
    4031. 

  4031.             )
    4032. 

  4032.         )
    4033. 

  4033.     )
    4034. 

  4034.     {
    4035. 

  4035.         BOOST_TEST_EQ(
    4036. 

  4036.             passed_by_lvalue_reference_to_const
    4037. 

  4037.           , U::evaluate_category&lt;0&gt;(args[_lrc])
    4038. 

  4038.         );
    4039. 

  4039.         BOOST_TEST_EQ(
    4040. 

  4040.             passed_by_lvalue_reference
    4041. 

  4041.           , U::evaluate_category&lt;1&gt;(args[_lr])
    4042. 

  4042.         );
    4043. 

  4043.         BOOST_TEST_EQ(
    4044. 

  4044.             passed_by_rvalue_reference_to_const
    4045. 

  4045.           , U::evaluate_category&lt;2&gt;(
    4046. 

  4046.                 args[_rrc0 | rvalue_const_bitset&lt;2&gt;()]
    4047. 

  4047.             )
    4048. 

  4048.         );
    4049. 

  4049.         BOOST_TEST_EQ(
    4050. 

  4050.             passed_by_rvalue_reference
    4051. 

  4051.           , U::evaluate_category&lt;3&gt;(
    4052. 

  4052.                 args[_rr0 | rvalue_bitset&lt;3&gt;()]
    4053. 

  4053.             )
    4054. 

  4054.         );
    4055. 

  4055. 

  4056.         return true;
    4057. 

  4057.     }
    4058. 

  4058. };
    4059. 

  4059. </pre>
    4060. 

  4060. <p>The following function calls are legal.</p>
    4061. 

  4061. <pre class="literal-block">
    4062. 

  4062. B::evaluate(  // positional arguments
    4063. 

  4063.     lvalue_const_bitset&lt;0&gt;()
    4064. 

  4064.   , lvalue_bitset&lt;1&gt;()
    4065. 

  4065.   , rvalue_const_bitset&lt;2&gt;()
    4066. 

  4066.   , rvalue_bitset&lt;3&gt;()
    4067. 

  4067. );
    4068. 

  4068. B::evaluate(  // positional arguments
    4069. 

  4069.     lvalue_const_bitset&lt;0&gt;()
    4070. 

  4070.   , lvalue_bitset&lt;1&gt;()
    4071. 

  4071. );
    4072. 

  4072. B::evaluate((  // composed arguments
    4073. 

  4073.     _rr0 = rvalue_bitset&lt;3&gt;()
    4074. 

  4074.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4075. 

  4075.   , _lr0 = lvalue_bitset&lt;1&gt;()
    4076. 

  4076.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    4077. 

  4077. ));
    4078. 

  4078. B::evaluate(  // named arguments
    4079. 

  4079.     _rr0 = rvalue_bitset&lt;3&gt;()
    4080. 

  4080.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4081. 

  4081.   , _lr0 = lvalue_bitset&lt;1&gt;()
    4082. 

  4082.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    4083. 

  4083. );
    4084. 

  4084. B::evaluate(  // named arguments
    4085. 

  4085.     _lr0 = lvalue_bitset&lt;1&gt;()
    4086. 

  4086.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4087. 

  4087. );
    4088. 

  4088. </pre>
    4089. 

  4089. <p>Because the parameters were wrapped in a <tt class="docutils literal">(deduced …)</tt> clause, the following
    4090. 

  4090. function calls are also legal.</p>
    4091. 

  4091. <pre class="literal-block">
    4092. 

  4092. B::evaluate(  // deduced arguments
    4093. 

  4093.     rvalue_bitset&lt;3&gt;()
    4094. 

  4094.   , lvalue_const_bitset&lt;0&gt;()
    4095. 

  4095.   , lvalue_bitset&lt;1&gt;()
    4096. 

  4096.   , rvalue_const_bitset&lt;2&gt;()
    4097. 

  4097. );
    4098. 

  4098. B::evaluate(  // deduced arguments
    4099. 

  4099.     lvalue_bitset&lt;1&gt;()
    4100. 

  4100.   , lvalue_const_bitset&lt;0&gt;()
    4101. 

  4101. );
    4102. 

  4102. </pre>
    4103. 

  4103. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> test program demonstrates proper usage of this macro.</p>
    4104. 

  4104. <p><strong>Macro parameters:</strong></p>
    4105. 

  4105. <ul class="simple">
    4106. 

  4106. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    4107. 

  4107. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    4108. 

  4108. generated forwarding functions.  <tt class="docutils literal">name</tt> may be qualified by the
    4109. 

  4109. <tt class="docutils literal">static</tt> keyword to declare the member function and its helpers as not
    4110. 

  4110. associated with any object of the enclosing type.</li>
    4111. 

  4111. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    4112. 

  4112. function resides.</li>
    4113. 

  4113. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    4114. 

  4114. <em>argument-specifiers</em>, as defined below.</li>
    4115. 

  4115. </ul>
    4116. 

  4116. <p><strong>Argument specifiers syntax:</strong></p>
    4117. 

  4117. <pre class="literal-block">
    4118. 

  4118. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    4119. 

  4119. 

  4120. specifier-group0 ::= <em>specifier-group1</em> |
    4121. 

  4121.     (
    4122. 

  4122.         '<strong>(</strong>' '<strong>deduced</strong>'
    4123. 

  4123.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    4124. 

  4124.         '<strong>)</strong>'
    4125. 

  4125.     )
    4126. 

  4126. 

  4127. specifier-group1 ::=
    4128. 

  4128.     (
    4129. 

  4129.         '<strong>(</strong>' '<strong>optional</strong>'
    4130. 

  4130.             <em>specifier</em> {<em>specifier</em>}
    4131. 

  4131.         '<strong>)</strong>'
    4132. 

  4132.     ) | (
    4133. 

  4133.         '<strong>(</strong>' '<strong>required</strong>'
    4134. 

  4134.             <em>specifier</em> {<em>specifier</em>}
    4135. 

  4135.         '<strong>)</strong>'
    4136. 

  4136.     )
    4137. 

  4137. 

  4138. specifier ::=
    4139. 

  4139.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    4140. 

  4140. 

  4141. restriction ::=
    4142. 

  4142.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    4143. 

  4143.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    4144. 

  4144.     '<strong>*</strong>'
    4145. 

  4145. </pre>
    4146. 

  4146. <ul class="simple">
    4147. 

  4147. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    4148. 

  4148. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    4149. 

  4149. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    4150. 

  4150. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    4151. 

  4151. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    4152. 

  4152. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    4153. 

  4153. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    4154. 

  4154. Metafunction Class</a> whose first argument will be the type of the
    4155. 

  4155. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    4156. 

  4156. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.</li>
    4157. 

  4157. </ul>
    4158. 

  4158. <p>Note that <em>specifier</em> does not include <em>default-value</em>.  It is up to the
    4159. 

  4159. function body to determine the default value of all optional arguments.</p>
    4160. 

  4160. <p><strong>Approximate expansion:</strong></p>
    4161. 

  4161. <p>Where:</p>
    4162. 

  4162. <ul class="simple">
    4163. 

  4163. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    4164. 

  4164. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    4165. 

  4165. </ul>
    4166. 

  4166. <pre class="literal-block">
    4167. 

  4167. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    4168. 

  4168. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    4169. 

  4169. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    4170. 

  4170. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    4171. 

  4171. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    4172. 

  4172. template &lt;typename Args&gt;
    4173. 

  4173. using boost_param_result_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    4174. 

  4174. 

  4175. // If <strong>result</strong> is a simple return type:
    4176. 

  4176. template &lt;typename Args&gt;
    4177. 

  4177. struct boost_param_result_ ## __LINE__ ## <strong>name</strong>
    4178. 

  4178. {
    4179. 

  4179.     typedef <strong>result</strong> type;
    4180. 

  4180. };
    4181. 

  4181. 

  4182. struct boost_param_params_ ## __LINE__ ## <strong>name</strong>
    4183. 

  4183.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    4184. 

  4184.         <em>list of parameter specifications, based on arguments</em>
    4185. 

  4185.     &gt;
    4186. 

  4186. {
    4187. 

  4187. };
    4188. 

  4188. 

  4189. typedef boost_param_params_ ## __LINE__ ## <strong>name</strong>
    4190. 

  4190.     boost_param_parameters_ ## __LINE__ ## <strong>name</strong>;
    4191. 

  4191. 

  4192. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    4193. 

  4193. <strong>result</strong> <strong>name</strong>(
    4194. 

  4194.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    4195. 

  4195.   , typename boost_param_parameters_ ## __LINE__ ## <strong>name</strong>
    4196. 

  4196.     ::match&lt;A0, …, A ## <strong>n</strong>&gt;::type
    4197. 

  4197.     = boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()
    4198. 

  4198. )
    4199. 

  4199. {
    4200. 

  4200.     return this-&gt;boost_param_impl ## <strong>name</strong>(
    4201. 

  4201.         boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()(
    4202. 

  4202.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    4203. 

  4203.           , …
    4204. 

  4204.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    4205. 

  4205.         )
    4206. 

  4206.     );
    4207. 

  4207. }
    4208. 

  4208. 

  4209. <span class="vellipsis">⋮</span>
    4210. 

  4210. 

  4211. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    4212. 

  4212. <strong>result</strong> <strong>name</strong>(
    4213. 

  4213.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    4214. 

  4214.   , typename boost_param_parameters_ ## __LINE__ ## <strong>name</strong>
    4215. 

  4215.     ::match&lt;A0, …, A ## <strong>m</strong>&gt;::type
    4216. 

  4216.     = boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()
    4217. 

  4217. )
    4218. 

  4218. {
    4219. 

  4219.     return this-&gt;boost_param_impl ## <strong>name</strong>(
    4220. 

  4220.         boost_param_parameters_ ## __LINE__ ## <strong>name</strong>()(
    4221. 

  4221.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    4222. 

  4222.           , …
    4223. 

  4223.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    4224. 

  4224.         )
    4225. 

  4225.     );
    4226. 

  4226. }
    4227. 

  4227. 

  4228. template &lt;typename Args&gt;
    4229. 

  4229. typename boost_param_result_ ## __LINE__ ## <strong>name</strong>&lt;Args&gt;::type
    4230. 

  4230.     boost_param_impl ## <strong>name</strong>(Args const&amp; args)
    4231. 

  4231. </pre>
    4232. 

  4232. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    4233. 

  4233. available for use within the function body.</p>
    4234. 

  4234. </div>
    4235. 

  4235. <div class="section" id="boost-parameter-basic-const-member-function-result-name-tag-ns-args">
    4236. 

  4236. <span id="boost-parameter-basic-const-member-function"></span><h2><a class="toc-backref" href="#id65">7.9&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION(result, name, tag_ns, args)</tt></a></h2>
    4237. 

  4237. <table class="docutils field-list" frame="void" rules="none">
    4238. 

  4238. <col class="field-name" />
    4239. 

  4239. <col class="field-body" />
    4240. 

  4240. <tbody valign="top">
    4241. 

  4241. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    4242. 

  4242. </tr>
    4243. 

  4243. </tbody>
    4244. 

  4244. </table>
    4245. 

  4245. <p>Generates a member function that can take in positional arguments, composed
    4246. 

  4246. arguments, named arguments, and deduced arguments.</p>
    4247. 

  4247. <table class="docutils field-list" frame="void" rules="none">
    4248. 

  4248. <col class="field-name" />
    4249. 

  4249. <col class="field-body" />
    4250. 

  4250. <tbody valign="top">
    4251. 

  4251. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    4252. 

  4252. </tr>
    4253. 

  4253. </tbody>
    4254. 

  4254. </table>
    4255. 

  4255. <p>The return type of each of the following function templates falls under a
    4256. 

  4256. different value category.</p>
    4257. 

  4257. <pre class="literal-block">
    4258. 

  4258. template &lt;std::size_t N&gt;
    4259. 

  4259. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    4260. 

  4260. {
    4261. 

  4261.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    4262. 

  4262. }
    4263. 

  4263. 

  4264. template &lt;std::size_t N&gt;
    4265. 

  4265. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    4266. 

  4266. {
    4267. 

  4267.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    4268. 

  4268. }
    4269. 

  4269. 

  4270. template &lt;std::size_t N&gt;
    4271. 

  4271. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    4272. 

  4272. {
    4273. 

  4273.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    4274. 

  4274.     return lset;
    4275. 

  4275. }
    4276. 

  4276. 

  4277. template &lt;std::size_t N&gt;
    4278. 

  4278. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    4279. 

  4279. {
    4280. 

  4280.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    4281. 

  4281.     return clset;
    4282. 

  4282. }
    4283. 

  4283. </pre>
    4284. 

  4284. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    4285. 

  4285. to return the correct value category when passed in an object returned by one
    4286. 

  4286. of the functions defined above.  Assume that
    4287. 

  4287. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    4288. 

  4288. <pre class="literal-block">
    4289. 

  4289. enum invoked
    4290. 

  4290. {
    4291. 

  4291.     passed_by_lvalue_reference_to_const
    4292. 

  4292.   , passed_by_lvalue_reference
    4293. 

  4293.   , passed_by_rvalue_reference_to_const
    4294. 

  4294.   , passed_by_rvalue_reference
    4295. 

  4295. };
    4296. 

  4296. 

  4297. struct U
    4298. 

  4298. {
    4299. 

  4299.     template &lt;std::size_t N&gt;
    4300. 

  4300.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    4301. 

  4301.     {
    4302. 

  4302.         return passed_by_lvalue_reference_to_const;
    4303. 

  4303.     }
    4304. 

  4304. 

  4305.     template &lt;std::size_t N&gt;
    4306. 

  4306.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    4307. 

  4307.     {
    4308. 

  4308.         return passed_by_lvalue_reference;
    4309. 

  4309.     }
    4310. 

  4310. 

  4311.     template &lt;std::size_t N&gt;
    4312. 

  4312.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    4313. 

  4313.     {
    4314. 

  4314.         return passed_by_rvalue_reference_to_const;
    4315. 

  4315.     }
    4316. 

  4316. 

  4317.     template &lt;std::size_t N&gt;
    4318. 

  4318.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    4319. 

  4319.     {
    4320. 

  4320.         return passed_by_rvalue_reference;
    4321. 

  4321.     }
    4322. 

  4322. };
    4323. 

  4323. </pre>
    4324. 

  4324. <p>Define the named parameters that will comprise the argument specification that
    4325. 

  4325. this macro will use.  Ensure that all their tag types are in the same
    4326. 

  4326. namespace, which is <tt class="docutils literal">kw</tt> in this case.  The identifiers with leading
    4327. 

  4327. underscores can be passed to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    4328. 

  4328. same argument to which the corresponding named parameter (without underscores)
    4329. 

  4329. is bound, as will be shown later.</p>
    4330. 

  4330. <pre class="literal-block">
    4331. 

  4331. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw) in(lrc))
    4332. 

  4332. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw) in_out(lr))
    4333. 

  4333. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw) in(rrc))
    4334. 

  4334. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw) consume(rr))
    4335. 

  4335. </pre>
    4336. 

  4336. <p>Use the macro as a substitute for a normal <tt class="docutils literal">const</tt> member function
    4337. 

  4337. header.  Enclose the return type <tt class="docutils literal">bool</tt> in parentheses.  For each parameter,
    4338. 

  4338. also enclose the expected value type in parentheses.  Since the value types
    4339. 

  4339. are mutually exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    4340. 

  4340. clause.  Otherwise, just as with a normal function, the order in which you
    4341. 

  4341. specify the parameters determines their position.  However, unlike a normal
    4342. 

  4342. function, default values must be specified within the function body.  Also
    4343. 

  4343. within the function body, you must pass the matching identifier with the
    4344. 

  4344. leading underscore to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    4345. 

  4345. corresponding argument, but at least this doesn't require <tt class="docutils literal"><span class="pre">std::forward</span></tt> to
    4346. 

  4346. preserve value categories.</p>
    4347. 

  4347. <pre class="literal-block">
    4348. 

  4348. struct B
    4349. 

  4349. {
    4350. 

  4350.     B()
    4351. 

  4351.     {
    4352. 

  4352.     }
    4353. 

  4353. 

  4354.     BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION((bool), evaluate, kw,
    4355. 

  4355.         (deduced
    4356. 

  4356.             (required
    4357. 

  4357.                 (lrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;1&gt;))
    4358. 

  4358.                 (lr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;2&gt;))
    4359. 

  4359.             )
    4360. 

  4360.             (optional
    4361. 

  4361.                 (rrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;3&gt;))
    4362. 

  4362.                 (rr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;4&gt;))
    4363. 

  4363.             )
    4364. 

  4364.         )
    4365. 

  4365.     )
    4366. 

  4366.     {
    4367. 

  4367.         BOOST_TEST_EQ(
    4368. 

  4368.             passed_by_lvalue_reference_to_const
    4369. 

  4369.           , U::evaluate_category&lt;0&gt;(args[_lrc])
    4370. 

  4370.         );
    4371. 

  4371.         BOOST_TEST_EQ(
    4372. 

  4372.             passed_by_lvalue_reference
    4373. 

  4373.           , U::evaluate_category&lt;1&gt;(args[_lr])
    4374. 

  4374.         );
    4375. 

  4375.         BOOST_TEST_EQ(
    4376. 

  4376.             passed_by_rvalue_reference_to_const
    4377. 

  4377.           , U::evaluate_category&lt;2&gt;(
    4378. 

  4378.                 args[_rrc0 | rvalue_const_bitset&lt;2&gt;()]
    4379. 

  4379.             )
    4380. 

  4380.         );
    4381. 

  4381.         BOOST_TEST_EQ(
    4382. 

  4382.             passed_by_rvalue_reference
    4383. 

  4383.           , U::evaluate_category&lt;3&gt;(
    4384. 

  4384.                 args[_rr0 | rvalue_bitset&lt;3&gt;()]
    4385. 

  4385.             )
    4386. 

  4386.         );
    4387. 

  4387. 

  4388.         return true;
    4389. 

  4389.     }
    4390. 

  4390. };
    4391. 

  4391. </pre>
    4392. 

  4392. <p>The following function calls are legal.</p>
    4393. 

  4393. <pre class="literal-block">
    4394. 

  4394. B const b = B();
    4395. 

  4395. b.evaluate(  // positional arguments
    4396. 

  4396.     lvalue_const_bitset&lt;0&gt;()
    4397. 

  4397.   , lvalue_bitset&lt;1&gt;()
    4398. 

  4398.   , rvalue_const_bitset&lt;2&gt;()
    4399. 

  4399.   , rvalue_bitset&lt;3&gt;()
    4400. 

  4400. );
    4401. 

  4401. b.evaluate(  // positional arguments
    4402. 

  4402.     lvalue_const_bitset&lt;0&gt;()
    4403. 

  4403.   , lvalue_bitset&lt;1&gt;()
    4404. 

  4404. );
    4405. 

  4405. b.evaluate((  // composed arguments
    4406. 

  4406.     _rr0 = rvalue_bitset&lt;3&gt;()
    4407. 

  4407.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4408. 

  4408.   , _lr0 = lvalue_bitset&lt;1&gt;()
    4409. 

  4409.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    4410. 

  4410. ));
    4411. 

  4411. b.evaluate(  // named arguments
    4412. 

  4412.     _rr0 = rvalue_bitset&lt;3&gt;()
    4413. 

  4413.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4414. 

  4414.   , _lr0 = lvalue_bitset&lt;1&gt;()
    4415. 

  4415.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    4416. 

  4416. );
    4417. 

  4417. b.evaluate(  // named arguments
    4418. 

  4418.     _lr0 = lvalue_bitset&lt;1&gt;()
    4419. 

  4419.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4420. 

  4420. );
    4421. 

  4421. </pre>
    4422. 

  4422. <p>Because the parameters were wrapped in a <tt class="docutils literal">(deduced …)</tt> clause, the following
    4423. 

  4423. function calls are also legal.</p>
    4424. 

  4424. <pre class="literal-block">
    4425. 

  4425. b.evaluate(  // deduced arguments
    4426. 

  4426.     rvalue_bitset&lt;3&gt;()
    4427. 

  4427.   , lvalue_const_bitset&lt;0&gt;()
    4428. 

  4428.   , lvalue_bitset&lt;1&gt;()
    4429. 

  4429.   , rvalue_const_bitset&lt;2&gt;()
    4430. 

  4430. );
    4431. 

  4431. b.evaluate(  // deduced arguments
    4432. 

  4432.     lvalue_bitset&lt;1&gt;()
    4433. 

  4433.   , lvalue_const_bitset&lt;0&gt;()
    4434. 

  4434. );
    4435. 

  4435. </pre>
    4436. 

  4436. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> test program demonstrates proper usage of this macro.</p>
    4437. 

  4437. <p><strong>Macro parameters:</strong></p>
    4438. 

  4438. <ul class="simple">
    4439. 

  4439. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    4440. 

  4440. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    4441. 

  4441. generated forwarding functions.</li>
    4442. 

  4442. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    4443. 

  4443. function resides.</li>
    4444. 

  4444. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    4445. 

  4445. <em>argument-specifiers</em>, as defined below.</li>
    4446. 

  4446. </ul>
    4447. 

  4447. <p><strong>Argument specifiers syntax:</strong></p>
    4448. 

  4448. <pre class="literal-block">
    4449. 

  4449. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    4450. 

  4450. 

  4451. specifier-group0 ::= <em>specifier-group1</em> |
    4452. 

  4452.     (
    4453. 

  4453.         '<strong>(</strong>' '<strong>deduced</strong>'
    4454. 

  4454.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    4455. 

  4455.         '<strong>)</strong>'
    4456. 

  4456.     )
    4457. 

  4457. 

  4458. specifier-group1 ::=
    4459. 

  4459.     (
    4460. 

  4460.         '<strong>(</strong>' '<strong>optional</strong>'
    4461. 

  4461.             <em>specifier</em> {<em>specifier</em>}
    4462. 

  4462.         '<strong>)</strong>'
    4463. 

  4463.     ) | (
    4464. 

  4464.         '<strong>(</strong>' '<strong>required</strong>'
    4465. 

  4465.             <em>specifier</em> {<em>specifier</em>}
    4466. 

  4466.         '<strong>)</strong>'
    4467. 

  4467.     )
    4468. 

  4468. 

  4469. specifier ::=
    4470. 

  4470.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    4471. 

  4471. 

  4472. restriction ::=
    4473. 

  4473.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    4474. 

  4474.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    4475. 

  4475.     '<strong>*</strong>'
    4476. 

  4476. </pre>
    4477. 

  4477. <ul class="simple">
    4478. 

  4478. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    4479. 

  4479. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    4480. 

  4480. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    4481. 

  4481. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    4482. 

  4482. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    4483. 

  4483. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    4484. 

  4484. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    4485. 

  4485. Metafunction Class</a> whose first argument will be the type of the
    4486. 

  4486. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    4487. 

  4487. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.</li>
    4488. 

  4488. </ul>
    4489. 

  4489. <p>Note that <em>specifier</em> does not include <em>default-value</em>.  It is up to the
    4490. 

  4490. function body to determine the default value of all optional arguments.</p>
    4491. 

  4491. <p><strong>Approximate expansion:</strong></p>
    4492. 

  4492. <p>Where:</p>
    4493. 

  4493. <ul class="simple">
    4494. 

  4494. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    4495. 

  4495. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    4496. 

  4496. </ul>
    4497. 

  4497. <pre class="literal-block">
    4498. 

  4498. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    4499. 

  4499. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    4500. 

  4500. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    4501. 

  4501. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    4502. 

  4502. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    4503. 

  4503. template &lt;typename Args&gt;
    4504. 

  4504. using boost_param_result_const_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    4505. 

  4505. 

  4506. // If <strong>result</strong> is a simple return type:
    4507. 

  4507. template &lt;typename Args&gt;
    4508. 

  4508. struct boost_param_result_const_ ## __LINE__ ## <strong>name</strong>
    4509. 

  4509. {
    4510. 

  4510.     typedef <strong>result</strong> type;
    4511. 

  4511. };
    4512. 

  4512. 

  4513. struct boost_param_params_const_ ## __LINE__ ## <strong>name</strong>
    4514. 

  4514.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    4515. 

  4515.         <em>list of parameter specifications, based on arguments</em>
    4516. 

  4516.     &gt;
    4517. 

  4517. {
    4518. 

  4518. };
    4519. 

  4519. 

  4520. typedef boost_param_params_const_ ## __LINE__ ## <strong>name</strong>
    4521. 

  4521.     boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>;
    4522. 

  4522. 

  4523. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    4524. 

  4524. <strong>result</strong> <strong>name</strong>(
    4525. 

  4525.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    4526. 

  4526.   , typename boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>
    4527. 

  4527.     ::match&lt;A0, …, A ## <strong>n</strong>&gt;::type
    4528. 

  4528.     = boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>()
    4529. 

  4529. ) const
    4530. 

  4530. {
    4531. 

  4531.     return this-&gt;boost_param_impl_const ## __LINE__ ## <strong>name</strong>(
    4532. 

  4532.         boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>()(
    4533. 

  4533.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    4534. 

  4534.           , …
    4535. 

  4535.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    4536. 

  4536.         )
    4537. 

  4537.     );
    4538. 

  4538. }
    4539. 

  4539. 

  4540. <span class="vellipsis">⋮</span>
    4541. 

  4541. 

  4542. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    4543. 

  4543. <strong>result</strong> <strong>name</strong>(
    4544. 

  4544.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    4545. 

  4545.   , typename boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>
    4546. 

  4546.     ::match&lt;A0, …, A ## <strong>m</strong>&gt;::type
    4547. 

  4547.     = boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>()
    4548. 

  4548. ) const
    4549. 

  4549. {
    4550. 

  4550.     return this-&gt;boost_param_impl_const ## __LINE__ ## <strong>name</strong>(
    4551. 

  4551.         boost_param_parameters_const_ ## __LINE__ ## <strong>name</strong>()(
    4552. 

  4552.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    4553. 

  4553.           , …
    4554. 

  4554.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    4555. 

  4555.         )
    4556. 

  4556.     );
    4557. 

  4557. }
    4558. 

  4558. 

  4559. template &lt;typename Args&gt;
    4560. 

  4560. typename boost_param_result_const_ ## __LINE__ ## <strong>name</strong>&lt;Args&gt;::type
    4561. 

  4561.     boost_param_impl_const ## __LINE__ ## <strong>name</strong>(Args const&amp; args) const
    4562. 

  4562. </pre>
    4563. 

  4563. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    4564. 

  4564. available for use within the function body.</p>
    4565. 

  4565. </div>
    4566. 

  4566. <div class="section" id="boost-parameter-basic-function-call-operator-result-tag-ns-arguments">
    4567. 

  4567. <span id="boost-parameter-basic-function-call-operator"></span><h2><a class="toc-backref" href="#id66">7.10&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)</tt></a></h2>
    4568. 

  4568. <table class="docutils field-list" frame="void" rules="none">
    4569. 

  4569. <col class="field-name" />
    4570. 

  4570. <col class="field-body" />
    4571. 

  4571. <tbody valign="top">
    4572. 

  4572. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    4573. 

  4573. </tr>
    4574. 

  4574. </tbody>
    4575. 

  4575. </table>
    4576. 

  4576. <p>Generates a function call operator that can take in positional arguments,
    4577. 

  4577. composed arguments, named arguments, and deduced arguments.</p>
    4578. 

  4578. <table class="docutils field-list" frame="void" rules="none">
    4579. 

  4579. <col class="field-name" />
    4580. 

  4580. <col class="field-body" />
    4581. 

  4581. <tbody valign="top">
    4582. 

  4582. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    4583. 

  4583. </tr>
    4584. 

  4584. </tbody>
    4585. 

  4585. </table>
    4586. 

  4586. <p>Define the named parameters that will comprise the argument specification that
    4587. 

  4587. this macro will use.  Ensure that all their tag types are in the same
    4588. 

  4588. namespace, which is <tt class="docutils literal">tag</tt> by default.</p>
    4589. 

  4589. <pre class="literal-block">
    4590. 

  4590. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(y)
    4591. 

  4591. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(z)
    4592. 

  4592. </pre>
    4593. 

  4593. <p>Use the macro as a substitute for a normal function call operator
    4594. 

  4594. header.  Enclose the return type in parentheses.  For each parameter, also
    4595. 

  4595. enclose the expected value type in parentheses.  Since the value types are
    4596. 

  4596. mutually exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    4597. 

  4597. clause.  This is especially useful when implementing multiple
    4598. 

  4598. Boost.Parameter-enabled function call operator overloads.</p>
    4599. 

  4599. <pre class="literal-block">
    4600. 

  4600. class char_reader
    4601. 

  4601. {
    4602. 

  4602.     int index;
    4603. 

  4603.     char const* key;
    4604. 

  4604. 

  4605.  public:
    4606. 

  4606.     explicit char_reader(char const* k) : index(0), key(k)
    4607. 

  4607.     {
    4608. 

  4608.     }
    4609. 

  4609. 

  4610.     BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR((void), tag,
    4611. 

  4611.         (deduced
    4612. 

  4612.             (required
    4613. 

  4613.                 (y, (int))
    4614. 

  4614.                 (z, (char const*))
    4615. 

  4615.             )
    4616. 

  4616.         )
    4617. 

  4617.     )
    4618. 

  4618.     {
    4619. 

  4619.         this-&gt;index = args[_y];
    4620. 

  4620.         this-&gt;key = args[_z];
    4621. 

  4621.     }
    4622. 

  4622. 

  4623.     <a class="reference internal" href="#boost-parameter-basic-const-function-call-operator"><tt class="docutils literal">BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR</tt></a>((char), tag,
    4624. 

  4624.         (deduced
    4625. 

  4625.             (required
    4626. 

  4626.                 (y, (bool))
    4627. 

  4627.                 (z, (<a class="reference external" href="http://en.cppreference.com/w/cpp/container/map">std::map</a>&lt;char const*, <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>&gt;))
    4628. 

  4628.             )
    4629. 

  4629.         )
    4630. 

  4630.     )
    4631. 

  4631.     {
    4632. 

  4632.         return args[_y] ? (
    4633. 

  4633.             (args[_z].find(this-&gt;key)-&gt;second)[this-&gt;index]
    4634. 

  4634.         ) : this-&gt;key[this-&gt;index];
    4635. 

  4635.     }
    4636. 

  4636. };
    4637. 

  4637. </pre>
    4638. 

  4638. <p>As with regular argument-dependent lookup, the value types of the arguments
    4639. 

  4639. passed in determine which function call operator overload gets invoked.</p>
    4640. 

  4640. <pre class="literal-block">
    4641. 

  4641. char const* keys[] = {&quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;};
    4642. 

  4642. <a class="reference external" href="http://en.cppreference.com/w/cpp/container/map">std::map</a>&lt;char const*, <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>&gt; k2s;
    4643. 

  4643. k2s[keys[0]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;qux&quot;);
    4644. 

  4644. k2s[keys[1]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;wmb&quot;);
    4645. 

  4645. k2s[keys[2]] = <a class="reference external" href="http://en.cppreference.com/w/cpp/string/basic_string">std::string</a>(&quot;zxc&quot;);
    4646. 

  4646. char_reader r(keys[0]);
    4647. 

  4647. 

  4648. // positional arguments
    4649. 

  4649. BOOST_TEST_EQ('q', (r(true, k2s)));
    4650. 

  4650. BOOST_TEST_EQ('f', (r(false, k2s)));
    4651. 

  4651. 

  4652. // named arguments
    4653. 

  4653. r(_z = keys[1], _y = 1);
    4654. 

  4654. BOOST_TEST_EQ('m', (r(_z = k2s, _y = true)));
    4655. 

  4655. BOOST_TEST_EQ('a', (r(_z = k2s, _y = false)));
    4656. 

  4656. 

  4657. // deduced arguments
    4658. 

  4658. r(keys[2], 2);
    4659. 

  4659. BOOST_TEST_EQ('c', (r(k2s, true)));
    4660. 

  4660. BOOST_TEST_EQ('z', (r(k2s, false)));
    4661. 

  4661. </pre>
    4662. 

  4662. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> test program demonstrates proper usage of this macro.</p>
    4663. 

  4663. <p><strong>Macro parameters:</strong></p>
    4664. 

  4664. <ul class="simple">
    4665. 

  4665. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function call operator.</li>
    4666. 

  4666. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    4667. 

  4667. function call operator resides.</li>
    4668. 

  4668. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    4669. 

  4669. <em>argument-specifiers</em>, as defined below.</li>
    4670. 

  4670. </ul>
    4671. 

  4671. <p><strong>Argument specifiers syntax:</strong></p>
    4672. 

  4672. <pre class="literal-block">
    4673. 

  4673. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    4674. 

  4674. 

  4675. specifier-group0 ::= <em>specifier-group1</em> |
    4676. 

  4676.     (
    4677. 

  4677.         '<strong>(</strong>' '<strong>deduced</strong>'
    4678. 

  4678.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    4679. 

  4679.         '<strong>)</strong>'
    4680. 

  4680.     )
    4681. 

  4681. 

  4682. specifier-group1 ::=
    4683. 

  4683.     (
    4684. 

  4684.         '<strong>(</strong>' '<strong>optional</strong>'
    4685. 

  4685.             <em>specifier</em> {<em>specifier</em>}
    4686. 

  4686.         '<strong>)</strong>'
    4687. 

  4687.     ) | (
    4688. 

  4688.         '<strong>(</strong>' '<strong>required</strong>'
    4689. 

  4689.             <em>specifier</em> {<em>specifier</em>}
    4690. 

  4690.         '<strong>)</strong>'
    4691. 

  4691.     )
    4692. 

  4692. 

  4693. specifier ::=
    4694. 

  4694.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    4695. 

  4695. 

  4696. restriction ::=
    4697. 

  4697.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    4698. 

  4698.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    4699. 

  4699.     '<strong>*</strong>'
    4700. 

  4700. </pre>
    4701. 

  4701. <ul class="simple">
    4702. 

  4702. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    4703. 

  4703. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    4704. 

  4704. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    4705. 

  4705. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    4706. 

  4706. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    4707. 

  4707. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    4708. 

  4708. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    4709. 

  4709. Metafunction Class</a> whose first argument will be the type of the
    4710. 

  4710. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    4711. 

  4711. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.</li>
    4712. 

  4712. </ul>
    4713. 

  4713. <p>Note that <em>specifier</em> does not include <em>default-value</em>.  It is up to the
    4714. 

  4714. function body to determine the default value of all optional arguments.</p>
    4715. 

  4715. <p><strong>Approximate expansion:</strong></p>
    4716. 

  4716. <p>Where:</p>
    4717. 

  4717. <ul class="simple">
    4718. 

  4718. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    4719. 

  4719. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    4720. 

  4720. </ul>
    4721. 

  4721. <pre class="literal-block">
    4722. 

  4722. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    4723. 

  4723. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    4724. 

  4724. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    4725. 

  4725. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    4726. 

  4726. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    4727. 

  4727. template &lt;typename Args&gt;
    4728. 

  4728. using boost_param_result_ ## __LINE__ ## operator = <strong>result</strong>;
    4729. 

  4729. 

  4730. // If <strong>result</strong> is a simple return type:
    4731. 

  4731. template &lt;typename Args&gt;
    4732. 

  4732. struct boost_param_result_ ## __LINE__ ## operator
    4733. 

  4733. {
    4734. 

  4734.     typedef <strong>result</strong> type;
    4735. 

  4735. };
    4736. 

  4736. 

  4737. struct boost_param_params_ ## __LINE__ ## operator
    4738. 

  4738.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    4739. 

  4739.         <em>list of parameter specifications, based on arguments</em>
    4740. 

  4740.     &gt;
    4741. 

  4741. {
    4742. 

  4742. };
    4743. 

  4743. 

  4744. typedef boost_param_params_ ## __LINE__ ## operator
    4745. 

  4745.     boost_param_parameters_ ## __LINE__ ## operator;
    4746. 

  4746. 

  4747. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    4748. 

  4748. <strong>result</strong> operator()(
    4749. 

  4749.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    4750. 

  4750.   , typename boost_param_parameters_ ## __LINE__ ## operator::match&lt;
    4751. 

  4751.         A0, …, A ## <strong>n</strong>
    4752. 

  4752.     &gt;::type = boost_param_parameters_ ## __LINE__ ## operator()
    4753. 

  4753. )
    4754. 

  4754. {
    4755. 

  4755.     return this-&gt;boost_param_impl ## __LINE__ ## operator(
    4756. 

  4756.         boost_param_parameters_ ## __LINE__ ## operator()(
    4757. 

  4757.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    4758. 

  4758.           , …
    4759. 

  4759.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    4760. 

  4760.         )
    4761. 

  4761.     );
    4762. 

  4762. }
    4763. 

  4763. 

  4764. <span class="vellipsis">⋮</span>
    4765. 

  4765. 

  4766. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    4767. 

  4767. <strong>result</strong> operator()(
    4768. 

  4768.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    4769. 

  4769.   , typename boost_param_parameters_ ## __LINE__ ## operator::match&lt;
    4770. 

  4770.         A0, …, A ## <strong>m</strong>
    4771. 

  4771.     &gt;::type = boost_param_parameters_ ## __LINE__ ## operator()
    4772. 

  4772. )
    4773. 

  4773. {
    4774. 

  4774.     return this-&gt;boost_param_impl ## __LINE__ ## operator(
    4775. 

  4775.         boost_param_parameters_ ## __LINE__ ## operator()(
    4776. 

  4776.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    4777. 

  4777.           , …
    4778. 

  4778.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    4779. 

  4779.         )
    4780. 

  4780.     );
    4781. 

  4781. }
    4782. 

  4782. 

  4783. template &lt;typename Args&gt;
    4784. 

  4784. typename boost_param_result_ ## __LINE__ ## operator&lt;Args&gt;::type
    4785. 

  4785.     boost_param_impl ## __LINE__ ## operator(Args const&amp; args)
    4786. 

  4786. </pre>
    4787. 

  4787. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    4788. 

  4788. available for use within the function call operator body.</p>
    4789. 

  4789. </div>
    4790. 

  4790. <div class="section" id="boost-parameter-basic-const-function-call-operator-result-tag-ns-args">
    4791. 

  4791. <span id="boost-parameter-basic-const-function-call-operator"></span><h2><a class="toc-backref" href="#id67">7.11&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, args)</tt></a></h2>
    4792. 

  4792. <table class="docutils field-list" frame="void" rules="none">
    4793. 

  4793. <col class="field-name" />
    4794. 

  4794. <col class="field-body" />
    4795. 

  4795. <tbody valign="top">
    4796. 

  4796. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor.hpp">boost/parameter/preprocessor.hpp</a></td>
    4797. 

  4797. </tr>
    4798. 

  4798. </tbody>
    4799. 

  4799. </table>
    4800. 

  4800. <p>Generates a function call operator that can take in positional arguments,
    4801. 

  4801. composed arguments, named arguments, and deduced arguments.</p>
    4802. 

  4802. <table class="docutils field-list" frame="void" rules="none">
    4803. 

  4803. <col class="field-name" />
    4804. 

  4804. <col class="field-body" />
    4805. 

  4805. <tbody valign="top">
    4806. 

  4806. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    4807. 

  4807. </tr>
    4808. 

  4808. </tbody>
    4809. 

  4809. </table>
    4810. 

  4810. <p>The return type of each of the following function templates falls under a
    4811. 

  4811. different value category.</p>
    4812. 

  4812. <pre class="literal-block">
    4813. 

  4813. template &lt;std::size_t N&gt;
    4814. 

  4814. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    4815. 

  4815. {
    4816. 

  4816.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    4817. 

  4817. }
    4818. 

  4818. 

  4819. template &lt;std::size_t N&gt;
    4820. 

  4820. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    4821. 

  4821. {
    4822. 

  4822.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    4823. 

  4823. }
    4824. 

  4824. 

  4825. template &lt;std::size_t N&gt;
    4826. 

  4826. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    4827. 

  4827. {
    4828. 

  4828.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    4829. 

  4829.     return lset;
    4830. 

  4830. }
    4831. 

  4831. 

  4832. template &lt;std::size_t N&gt;
    4833. 

  4833. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    4834. 

  4834. {
    4835. 

  4835.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    4836. 

  4836.     return clset;
    4837. 

  4837. }
    4838. 

  4838. </pre>
    4839. 

  4839. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    4840. 

  4840. to return the correct value category when passed in an object returned by one
    4841. 

  4841. of the functions defined above.  Assume that
    4842. 

  4842. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    4843. 

  4843. <pre class="literal-block">
    4844. 

  4844. enum invoked
    4845. 

  4845. {
    4846. 

  4846.     passed_by_lvalue_reference_to_const
    4847. 

  4847.   , passed_by_lvalue_reference
    4848. 

  4848.   , passed_by_rvalue_reference_to_const
    4849. 

  4849.   , passed_by_rvalue_reference
    4850. 

  4850. };
    4851. 

  4851. 

  4852. struct U
    4853. 

  4853. {
    4854. 

  4854.     template &lt;std::size_t N&gt;
    4855. 

  4855.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    4856. 

  4856.     {
    4857. 

  4857.         return passed_by_lvalue_reference_to_const;
    4858. 

  4858.     }
    4859. 

  4859. 

  4860.     template &lt;std::size_t N&gt;
    4861. 

  4861.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    4862. 

  4862.     {
    4863. 

  4863.         return passed_by_lvalue_reference;
    4864. 

  4864.     }
    4865. 

  4865. 

  4866.     template &lt;std::size_t N&gt;
    4867. 

  4867.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    4868. 

  4868.     {
    4869. 

  4869.         return passed_by_rvalue_reference_to_const;
    4870. 

  4870.     }
    4871. 

  4871. 

  4872.     template &lt;std::size_t N&gt;
    4873. 

  4873.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    4874. 

  4874.     {
    4875. 

  4875.         return passed_by_rvalue_reference;
    4876. 

  4876.     }
    4877. 

  4877. };
    4878. 

  4878. </pre>
    4879. 

  4879. <p>Define the named parameters that will comprise the argument specification that
    4880. 

  4880. this macro will use.  Ensure that all their tag types are in the same
    4881. 

  4881. namespace, which is <tt class="docutils literal">kw</tt> in this case.  The identifiers with leading
    4882. 

  4882. underscores can be passed to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    4883. 

  4883. same argument to which the corresponding named parameter (without underscores)
    4884. 

  4884. is bound, as will be shown later.</p>
    4885. 

  4885. <pre class="literal-block">
    4886. 

  4886. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw) in(lrc))
    4887. 

  4887. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw) in_out(lr))
    4888. 

  4888. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw) in(rrc))
    4889. 

  4889. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw) consume(rr))
    4890. 

  4890. </pre>
    4891. 

  4891. <p>Use the macro as a substitute for a normal <tt class="docutils literal">const</tt> function call operator
    4892. 

  4892. header.  Enclose the return type <tt class="docutils literal">bool</tt> in parentheses.  For each parameter,
    4893. 

  4893. also enclose the expected value type in parentheses.  Since the value types
    4894. 

  4894. are mutually exclusive, you can wrap the parameters in a <tt class="docutils literal">(deduced …)</tt>
    4895. 

  4895. clause.  Otherwise, just as with a normal function, the order in which you
    4896. 

  4896. specify the parameters determines their position.  However, unlike a normal
    4897. 

  4897. function, default values must be specified within the function body.  Also
    4898. 

  4898. within the function body, you must pass the matching identifier with the
    4899. 

  4899. leading underscore to the bracket operator of <tt class="docutils literal">args</tt> to extract the
    4900. 

  4900. corresponding argument, but at least this doesn't require <tt class="docutils literal"><span class="pre">std::forward</span></tt> to
    4901. 

  4901. preserve value categories.</p>
    4902. 

  4902. <pre class="literal-block">
    4903. 

  4903. struct B
    4904. 

  4904. {
    4905. 

  4905.     B()
    4906. 

  4906.     {
    4907. 

  4907.     }
    4908. 

  4908. 

  4909.     BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR((bool), kw,
    4910. 

  4910.         (deduced
    4911. 

  4911.             (required
    4912. 

  4912.                 (lrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;1&gt;))
    4913. 

  4913.                 (lr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;2&gt;))
    4914. 

  4914.             )
    4915. 

  4915.             (optional
    4916. 

  4916.                 (rrc, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;3&gt;))
    4917. 

  4917.                 (rr, (<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;4&gt;))
    4918. 

  4918.             )
    4919. 

  4919.         )
    4920. 

  4920.     )
    4921. 

  4921.     {
    4922. 

  4922.         BOOST_TEST_EQ(
    4923. 

  4923.             passed_by_lvalue_reference_to_const
    4924. 

  4924.           , U::evaluate_category&lt;0&gt;(args[_lrc])
    4925. 

  4925.         );
    4926. 

  4926.         BOOST_TEST_EQ(
    4927. 

  4927.             passed_by_lvalue_reference
    4928. 

  4928.           , U::evaluate_category&lt;1&gt;(args[_lr])
    4929. 

  4929.         );
    4930. 

  4930.         BOOST_TEST_EQ(
    4931. 

  4931.             passed_by_rvalue_reference_to_const
    4932. 

  4932.           , U::evaluate_category&lt;2&gt;(
    4933. 

  4933.                 args[_rrc0 | rvalue_const_bitset&lt;2&gt;()]
    4934. 

  4934.             )
    4935. 

  4935.         );
    4936. 

  4936.         BOOST_TEST_EQ(
    4937. 

  4937.             passed_by_rvalue_reference
    4938. 

  4938.           , U::evaluate_category&lt;3&gt;(
    4939. 

  4939.                 args[_rr0 | rvalue_bitset&lt;3&gt;()]
    4940. 

  4940.             )
    4941. 

  4941.         );
    4942. 

  4942. 

  4943.         return true;
    4944. 

  4944.     }
    4945. 

  4945. };
    4946. 

  4946. </pre>
    4947. 

  4947. <p>The following function calls are legal.</p>
    4948. 

  4948. <pre class="literal-block">
    4949. 

  4949. B const b = B();
    4950. 

  4950. b(  // positional arguments
    4951. 

  4951.     lvalue_const_bitset&lt;0&gt;()
    4952. 

  4952.   , lvalue_bitset&lt;1&gt;()
    4953. 

  4953.   , rvalue_const_bitset&lt;2&gt;()
    4954. 

  4954.   , rvalue_bitset&lt;3&gt;()
    4955. 

  4955. );
    4956. 

  4956. b(  // positional arguments
    4957. 

  4957.     lvalue_const_bitset&lt;0&gt;()
    4958. 

  4958.   , lvalue_bitset&lt;1&gt;()
    4959. 

  4959. );
    4960. 

  4960. b((  // composed arguments
    4961. 

  4961.     _rr0 = rvalue_bitset&lt;3&gt;()
    4962. 

  4962.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4963. 

  4963.   , _lr0 = lvalue_bitset&lt;1&gt;()
    4964. 

  4964.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    4965. 

  4965. ));
    4966. 

  4966. b(  // named arguments
    4967. 

  4967.     _rr0 = rvalue_bitset&lt;3&gt;()
    4968. 

  4968.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4969. 

  4969.   , _lr0 = lvalue_bitset&lt;1&gt;()
    4970. 

  4970.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    4971. 

  4971. );
    4972. 

  4972. b(  // named arguments
    4973. 

  4973.     _lr0 = lvalue_bitset&lt;1&gt;()
    4974. 

  4974.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    4975. 

  4975. );
    4976. 

  4976. </pre>
    4977. 

  4977. <p>Because the parameters were wrapped in a <tt class="docutils literal">(deduced …)</tt> clause, the following
    4978. 

  4978. function calls are also legal.</p>
    4979. 

  4979. <pre class="literal-block">
    4980. 

  4980. b(  // deduced arguments
    4981. 

  4981.     rvalue_bitset&lt;3&gt;()
    4982. 

  4982.   , lvalue_const_bitset&lt;0&gt;()
    4983. 

  4983.   , lvalue_bitset&lt;1&gt;()
    4984. 

  4984.   , rvalue_const_bitset&lt;2&gt;()
    4985. 

  4985. );
    4986. 

  4986. b(  // deduced arguments
    4987. 

  4987.     lvalue_bitset&lt;1&gt;()
    4988. 

  4988.   , lvalue_const_bitset&lt;0&gt;()
    4989. 

  4989. );
    4990. 

  4990. </pre>
    4991. 

  4991. <p>The <a class="reference external" href="../../test/preprocessor.cpp">preprocessor.cpp</a> test program demonstrates proper usage of this macro.</p>
    4992. 

  4992. <p><strong>Macro parameters:</strong></p>
    4993. 

  4993. <ul class="simple">
    4994. 

  4994. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function call operator.</li>
    4995. 

  4995. <li><tt class="docutils literal">tag_namespace</tt> is the namespace in which the keywords used by the
    4996. 

  4996. function call operator resides.</li>
    4997. 

  4997. <li><tt class="docutils literal">arguments</tt> is a <a class="reference external" href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> <a class="reference external" href="../../../preprocessor/doc/data/sequences.html">sequence</a> of
    4998. 

  4998. <em>argument-specifiers</em>, as defined below.</li>
    4999. 

  4999. </ul>
    5000. 

  5000. <p><strong>Argument specifiers syntax:</strong></p>
    5001. 

  5001. <pre class="literal-block">
    5002. 

  5002. argument-specifiers ::= <em>specifier-group0</em> {<em>specifier-group0</em>}
    5003. 

  5003. 

  5004. specifier-group0 ::= <em>specifier-group1</em> |
    5005. 

  5005.     (
    5006. 

  5006.         '<strong>(</strong>' '<strong>deduced</strong>'
    5007. 

  5007.             <em>specifier-group1</em> {<em>specifier-group1</em>}
    5008. 

  5008.         '<strong>)</strong>'
    5009. 

  5009.     )
    5010. 

  5010. 

  5011. specifier-group1 ::=
    5012. 

  5012.     (
    5013. 

  5013.         '<strong>(</strong>' '<strong>optional</strong>'
    5014. 

  5014.             <em>specifier</em> {<em>specifier</em>}
    5015. 

  5015.         '<strong>)</strong>'
    5016. 

  5016.     ) | (
    5017. 

  5017.         '<strong>(</strong>' '<strong>required</strong>'
    5018. 

  5018.             <em>specifier</em> {<em>specifier</em>}
    5019. 

  5019.         '<strong>)</strong>'
    5020. 

  5020.     )
    5021. 

  5021. 

  5022. specifier ::=
    5023. 

  5023.     '<strong>(</strong>' <em>argument-name</em> '<strong>,</strong>' <em>restriction</em> ')'
    5024. 

  5024. 

  5025. restriction ::=
    5026. 

  5026.     ( '<strong>*</strong>' '<strong>(</strong>' <em>mfc</em> '<strong>)</strong>' ) |
    5027. 

  5027.     ( '<strong>(</strong>' <em>type-name</em> '<strong>)</strong>' ) |
    5028. 

  5028.     '<strong>*</strong>'
    5029. 

  5029. </pre>
    5030. 

  5030. <ul class="simple">
    5031. 

  5031. <li><tt class="docutils literal"><span class="pre">argument-name</span></tt> is any valid C++ identifier.</li>
    5032. 

  5032. <li><tt class="docutils literal">mfc</tt> is an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary Metafunction Class</a> whose first argument will
    5033. 

  5033. be the type of the corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument
    5034. 

  5034. will be the entire <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is a <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean
    5035. 

  5035. Integral Constant</a>; however, user code <em>cannot</em> compute <tt class="docutils literal">mfc</tt> in terms
    5036. 

  5036. of <tt class="docutils literal"><span class="pre">previous-name</span> ## _type</tt>.</li>
    5037. 

  5037. <li><tt class="docutils literal"><span class="pre">type-name</span></tt> is either the name of a <strong>target type</strong> or an <a class="reference external" href="../../../mpl/doc/refmanual/metafunction-class.html">MPL Binary
    5038. 

  5038. Metafunction Class</a> whose first argument will be the type of the
    5039. 

  5039. corresponding <tt class="docutils literal"><span class="pre">argument-name</span></tt>, whose second argument will be the entire
    5040. 

  5040. <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>, and whose return type is the <strong>target type</strong>.</li>
    5041. 

  5041. </ul>
    5042. 

  5042. <p>Note that <em>specifier</em> does not include <em>default-value</em>.  It is up to the
    5043. 

  5043. function body to determine the default value of all optional arguments.</p>
    5044. 

  5044. <p><strong>Approximate expansion:</strong></p>
    5045. 

  5045. <p>Where:</p>
    5046. 

  5046. <ul class="simple">
    5047. 

  5047. <li><tt class="docutils literal">n</tt> denotes the <em>minimum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    5048. 

  5048. <li><tt class="docutils literal">m</tt> denotes the <em>maximum</em> arity, as determined from <tt class="docutils literal">arguments</tt>.</li>
    5049. 

  5049. </ul>
    5050. 

  5050. <pre class="literal-block">
    5051. 

  5051. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    5052. 

  5052. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    5053. 

  5053. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    5054. 

  5054. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    5055. 

  5055. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    5056. 

  5056. template &lt;typename Args&gt;
    5057. 

  5057. using boost_param_result_const_ ## __LINE__ ## operator = <strong>result</strong>;
    5058. 

  5058. 

  5059. // If <strong>result</strong> is a simple return type:
    5060. 

  5060. template &lt;typename Args&gt;
    5061. 

  5061. struct boost_param_result_const_ ## __LINE__ ## operator
    5062. 

  5062. {
    5063. 

  5063.     typedef <strong>result</strong> type;
    5064. 

  5064. };
    5065. 

  5065. 

  5066. struct boost_param_params_const_ ## __LINE__ ## operator
    5067. 

  5067.   : <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    5068. 

  5068.         <em>list of parameter specifications, based on arguments</em>
    5069. 

  5069.     &gt;
    5070. 

  5070. {
    5071. 

  5071. };
    5072. 

  5072. 

  5073. typedef boost_param_params_const_ ## __LINE__ ## operator
    5074. 

  5074.     boost_param_parameters_const_ ## __LINE__ ## operator;
    5075. 

  5075. 

  5076. template &lt;typename A0, …, typename A ## <strong>n</strong>&gt;
    5077. 

  5077. <strong>result</strong> operator()(
    5078. 

  5078.     A0&amp;&amp; a0, …, A ## <strong>n</strong>&amp;&amp; a ## <strong>n</strong>
    5079. 

  5079.   , typename boost_param_parameters_const_ ## __LINE__ ## operator
    5080. 

  5080.     ::match&lt;A0, …, A ## <strong>n</strong>&gt;::type
    5081. 

  5081.     = boost_param_parameters_const_ ## __LINE__ ## operator()
    5082. 

  5082. ) const
    5083. 

  5083. {
    5084. 

  5084.     return this-&gt;boost_param_impl_const ## __LINE__ ## operator(
    5085. 

  5085.         boost_param_parameters_const_ ## __LINE__ ## operator()(
    5086. 

  5086.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    5087. 

  5087.           , …
    5088. 

  5088.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>n</strong>&gt;(a ## <strong>n</strong>)
    5089. 

  5089.         )
    5090. 

  5090.     );
    5091. 

  5091. }
    5092. 

  5092. 

  5093. <span class="vellipsis">⋮</span>
    5094. 

  5094. 

  5095. template &lt;typename A0, …, typename A ## <strong>m</strong>&gt;
    5096. 

  5096. <strong>result</strong> operator()(
    5097. 

  5097.     A0&amp;&amp; a0, …, A ## <strong>m</strong>&amp;&amp; a ## <strong>m</strong>
    5098. 

  5098.   , typename boost_param_parameters_const_ ## __LINE__ ## operator
    5099. 

  5099.     ::match&lt;A0, …, A ## <strong>m</strong>&gt;::type
    5100. 

  5100.     = boost_param_parameters_const_ ## __LINE__ ## operator()
    5101. 

  5101. ) const
    5102. 

  5102. {
    5103. 

  5103.     return this-&gt;boost_param_impl_const ## __LINE__ ## operator(
    5104. 

  5104.         boost_param_parameters_const_ ## __LINE__ ## operator()(
    5105. 

  5105.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A0&gt;(a0)
    5106. 

  5106.           , …
    5107. 

  5107.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>m</strong>&gt;(a ## <strong>m</strong>)
    5108. 

  5108.         )
    5109. 

  5109.     );
    5110. 

  5110. }
    5111. 

  5111. 

  5112. template &lt;typename Args&gt;
    5113. 

  5113. typename boost_param_result_const_ ## __LINE__ ## operator&lt;Args&gt;::type
    5114. 

  5114.     boost_param_impl_const ## __LINE__ ## operator(Args const&amp; args) const
    5115. 

  5115. </pre>
    5116. 

  5116. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    5117. 

  5117. available for use within the function call operator body.</p>
    5118. 

  5118. </div>
    5119. 

  5119. <div class="section" id="boost-parameter-no-spec-function-result-name">
    5120. 

  5120. <span id="boost-parameter-no-spec-function"></span><h2><a class="toc-backref" href="#id68">7.12&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_FUNCTION(result, name)</tt></a></h2>
    5121. 

  5121. <table class="docutils field-list" frame="void" rules="none">
    5122. 

  5122. <col class="field-name" />
    5123. 

  5123. <col class="field-body" />
    5124. 

  5124. <tbody valign="top">
    5125. 

  5125. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor_no_spec.hpp">boost/parameter/preprocessor_no_spec.hpp</a></td>
    5126. 

  5126. </tr>
    5127. 

  5127. </tbody>
    5128. 

  5128. </table>
    5129. 

  5129. <p>Generates a function that can take in named arguments.</p>
    5130. 

  5130. <table class="docutils field-list" frame="void" rules="none">
    5131. 

  5131. <col class="field-name" />
    5132. 

  5132. <col class="field-body" />
    5133. 

  5133. <tbody valign="top">
    5134. 

  5134. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    5135. 

  5135. </tr>
    5136. 

  5136. </tbody>
    5137. 

  5137. </table>
    5138. 

  5138. <p>The return type of each of the following function templates falls under a
    5139. 

  5139. different value category.</p>
    5140. 

  5140. <pre class="literal-block">
    5141. 

  5141. template &lt;std::size_t N&gt;
    5142. 

  5142. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    5143. 

  5143. {
    5144. 

  5144.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5145. 

  5145. }
    5146. 

  5146. 

  5147. template &lt;std::size_t N&gt;
    5148. 

  5148. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    5149. 

  5149. {
    5150. 

  5150.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5151. 

  5151. }
    5152. 

  5152. 

  5153. template &lt;std::size_t N&gt;
    5154. 

  5154. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    5155. 

  5155. {
    5156. 

  5156.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5157. 

  5157.     return lset;
    5158. 

  5158. }
    5159. 

  5159. 

  5160. template &lt;std::size_t N&gt;
    5161. 

  5161. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    5162. 

  5162. {
    5163. 

  5163.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5164. 

  5164.     return clset;
    5165. 

  5165. }
    5166. 

  5166. </pre>
    5167. 

  5167. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    5168. 

  5168. to return the correct value category when passed in an object returned by one
    5169. 

  5169. of the functions defined above.  Assume that
    5170. 

  5170. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    5171. 

  5171. <pre class="literal-block">
    5172. 

  5172. enum invoked
    5173. 

  5173. {
    5174. 

  5174.     passed_by_lvalue_reference_to_const
    5175. 

  5175.   , passed_by_lvalue_reference
    5176. 

  5176.   , passed_by_rvalue_reference_to_const
    5177. 

  5177.   , passed_by_rvalue_reference
    5178. 

  5178. };
    5179. 

  5179. 

  5180. struct U
    5181. 

  5181. {
    5182. 

  5182.     template &lt;std::size_t N&gt;
    5183. 

  5183.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    5184. 

  5184.     {
    5185. 

  5185.         return passed_by_lvalue_reference_to_const;
    5186. 

  5186.     }
    5187. 

  5187. 

  5188.     template &lt;std::size_t N&gt;
    5189. 

  5189.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    5190. 

  5190.     {
    5191. 

  5191.         return passed_by_lvalue_reference;
    5192. 

  5192.     }
    5193. 

  5193. 

  5194.     template &lt;std::size_t N&gt;
    5195. 

  5195.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    5196. 

  5196.     {
    5197. 

  5197.         return passed_by_rvalue_reference_to_const;
    5198. 

  5198.     }
    5199. 

  5199. 

  5200.     template &lt;std::size_t N&gt;
    5201. 

  5201.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    5202. 

  5202.     {
    5203. 

  5203.         return passed_by_rvalue_reference;
    5204. 

  5204.     }
    5205. 

  5205. };
    5206. 

  5206. </pre>
    5207. 

  5207. <p>Named parameters are required when invoking the function; however, none of
    5208. 

  5208. their tags need to be in the same namespace.</p>
    5209. 

  5209. <pre class="literal-block">
    5210. 

  5210. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw0) in(lrc))
    5211. 

  5211. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw1) in_out(lr))
    5212. 

  5212. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw2) in(rrc))
    5213. 

  5213. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw3) consume(rr))
    5214. 

  5214. </pre>
    5215. 

  5215. <p>Use the macro as a substitute for a variadic function header.  Enclose the
    5216. 

  5216. return type <tt class="docutils literal">bool</tt> in parentheses.</p>
    5217. 

  5217. <pre class="literal-block">
    5218. 

  5218. BOOST_PARAMETER_NO_SPEC_FUNCTION((bool), evaluate)
    5219. 

  5219. {
    5220. 

  5220.     BOOST_TEST_EQ(
    5221. 

  5221.         passed_by_lvalue_reference_to_const
    5222. 

  5222.       , U::evaluate_category&lt;0&gt;(args[_lrc])
    5223. 

  5223.     );
    5224. 

  5224.     BOOST_TEST_EQ(
    5225. 

  5225.         passed_by_lvalue_reference
    5226. 

  5226.       , U::evaluate_category&lt;1&gt;(args[_lr])
    5227. 

  5227.     );
    5228. 

  5228.     BOOST_TEST_EQ(
    5229. 

  5229.         passed_by_rvalue_reference_to_const
    5230. 

  5230.       , U::evaluate_category&lt;2&gt;(
    5231. 

  5231.             args[_rrc | rvalue_const_bitset&lt;2&gt;()]
    5232. 

  5232.         )
    5233. 

  5233.     );
    5234. 

  5234.     BOOST_TEST_EQ(
    5235. 

  5235.         passed_by_rvalue_reference
    5236. 

  5236.       , U::evaluate_category&lt;3&gt;(args[_rr | rvalue_bitset&lt;3&gt;()])
    5237. 

  5237.     );
    5238. 

  5238. 

  5239.     return true;
    5240. 

  5240. }
    5241. 

  5241. </pre>
    5242. 

  5242. <p>To invoke the function, bind all its arguments to named parameters.</p>
    5243. 

  5243. <pre class="literal-block">
    5244. 

  5244. evaluate(
    5245. 

  5245.     _rr0 = rvalue_bitset&lt;3&gt;()
    5246. 

  5246.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    5247. 

  5247.   , _lr0 = lvalue_bitset&lt;1&gt;()
    5248. 

  5248.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    5249. 

  5249. );
    5250. 

  5250. evaluate(
    5251. 

  5251.     _lr0 = lvalue_bitset&lt;1&gt;()
    5252. 

  5252.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    5253. 

  5253. );
    5254. 

  5254. </pre>
    5255. 

  5255. <p>The <a class="reference external" href="../../test/preprocessor_eval_cat_no_spec.cpp">preprocessor_eval_cat_no_spec.cpp</a> test program demonstrates proper usage of
    5256. 

  5256. this macro.</p>
    5257. 

  5257. <p><strong>Macro parameters:</strong></p>
    5258. 

  5258. <ul class="simple">
    5259. 

  5259. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    5260. 

  5260. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    5261. 

  5261. generated implementation function.</li>
    5262. 

  5262. </ul>
    5263. 

  5263. <p><strong>Argument specifiers syntax:</strong></p>
    5264. 

  5264. <p>None.</p>
    5265. 

  5265. <p><strong>Approximate expansion:</strong></p>
    5266. 

  5266. <pre class="literal-block">
    5267. 

  5267. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    5268. 

  5268. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    5269. 

  5269. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    5270. 

  5270. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    5271. 

  5271. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    5272. 

  5272. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5273. 

  5273. using boost_param_no_spec_result_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    5274. 

  5274. 

  5275. // If <strong>result</strong> is a simple return type:
    5276. 

  5276. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5277. 

  5277. struct boost_param_no_spec_result_ ## __LINE__ ## <strong>name</strong>
    5278. 

  5278. {
    5279. 

  5279.     typedef <strong>result</strong> type;
    5280. 

  5280. };
    5281. 

  5281. 

  5282. template &lt;typename ResultType, typename Args&gt;
    5283. 

  5283. ResultType
    5284. 

  5284.     boost_param_no_spec_impl ## __LINE__ ## <strong>name</strong>(
    5285. 

  5285.         (ResultType(*)())
    5286. 

  5286.       , Args const&amp; args
    5287. 

  5287.     );
    5288. 

  5288. 

  5289. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5290. 

  5290. inline typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>&lt;
    5291. 

  5291.     <a class="reference internal" href="#are-tagged-arguments"><tt class="docutils literal">are_tagged_arguments</tt></a>&lt;TaggedArg0,TaggedArgs...&gt;
    5292. 

  5292.   , boost_param_no_spec_result_ ## __LINE__ ## <strong>name</strong>&lt;
    5293. 

  5293.         TaggedArg0
    5294. 

  5294.       , TaggedArgs...
    5295. 

  5295.     &gt;
    5296. 

  5296. &gt;::type
    5297. 

  5297.     <strong>name</strong>(TaggedArg0 const&amp; arg0, TaggedArgs const&amp;... args)
    5298. 

  5298. {
    5299. 

  5299.     return boost_param_no_spec_impl ## __LINE__ ## <strong>name</strong>(
    5300. 

  5300.         static_cast&lt;
    5301. 

  5301.             typename
    5302. 

  5302.             boost_param_no_spec_result_ ## __LINE__ ## <strong>name</strong>&lt;
    5303. 

  5303.                 TaggedArg0
    5304. 

  5304.               , TaggedArgs...
    5305. 

  5305.             &gt;::type(*)()
    5306. 

  5306.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    5307. 

  5307.       , <a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a>(arg0, args...)
    5308. 

  5308.     );
    5309. 

  5309. }
    5310. 

  5310. 

  5311. template &lt;typename ResultType, typename Args&gt;
    5312. 

  5312. ResultType
    5313. 

  5313.     boost_param_no_spec_impl ## __LINE__ ## <strong>name</strong>(
    5314. 

  5314.         (ResultType(*)())
    5315. 

  5315.       , Args const&amp; args
    5316. 

  5316.     )
    5317. 

  5317. </pre>
    5318. 

  5318. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    5319. 

  5319. available for use within the function body.</p>
    5320. 

  5320. </div>
    5321. 

  5321. <div class="section" id="boost-parameter-no-spec-member-function-result-name">
    5322. 

  5322. <span id="boost-parameter-no-spec-member-function"></span><h2><a class="toc-backref" href="#id69">7.13&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION(result, name)</tt></a></h2>
    5323. 

  5323. <table class="docutils field-list" frame="void" rules="none">
    5324. 

  5324. <col class="field-name" />
    5325. 

  5325. <col class="field-body" />
    5326. 

  5326. <tbody valign="top">
    5327. 

  5327. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor_no_spec.hpp">boost/parameter/preprocessor_no_spec.hpp</a></td>
    5328. 

  5328. </tr>
    5329. 

  5329. </tbody>
    5330. 

  5330. </table>
    5331. 

  5331. <p>Generates a member function that can take in named arguments.</p>
    5332. 

  5332. <table class="docutils field-list" frame="void" rules="none">
    5333. 

  5333. <col class="field-name" />
    5334. 

  5334. <col class="field-body" />
    5335. 

  5335. <tbody valign="top">
    5336. 

  5336. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    5337. 

  5337. </tr>
    5338. 

  5338. </tbody>
    5339. 

  5339. </table>
    5340. 

  5340. <p>When designing a front-end class template whose back-end is configurable via
    5341. 

  5341. parameterized inheritance, it can be useful to omit argument specifiers from
    5342. 

  5342. a named-parameter member function so that the delegate member functions of the
    5343. 

  5343. back-end classes can enforce their own specifications.</p>
    5344. 

  5344. <pre class="literal-block">
    5345. 

  5345. template &lt;typename B&gt;
    5346. 

  5346. struct frontend : B
    5347. 

  5347. {
    5348. 

  5348.     frontend() : B()
    5349. 

  5349.     {
    5350. 

  5350.     }
    5351. 

  5351. 

  5352.     BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION((void), initialize)
    5353. 

  5353.     {
    5354. 

  5354.         this-&gt;initialize_impl(args);
    5355. 

  5355.     }
    5356. 

  5356. };
    5357. 

  5357. </pre>
    5358. 

  5358. <p>Named parameters are required when invoking the member function; however, none
    5359. 

  5359. of their tags need to be in the same namespace.</p>
    5360. 

  5360. <pre class="literal-block">
    5361. 

  5361. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a0)
    5362. 

  5362. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a1)
    5363. 

  5363. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a2)
    5364. 

  5364. </pre>
    5365. 

  5365. <p>For this example, each of the back-end class templates requires its own
    5366. 

  5366. parameter to be present in the argument pack.  In practice, such parameters
    5367. 

  5367. should be optional, with default values.</p>
    5368. 

  5368. <pre class="literal-block">
    5369. 

  5369. template &lt;typename T&gt;
    5370. 

  5370. class backend0
    5371. 

  5371. {
    5372. 

  5372.     T a0;
    5373. 

  5373. 

  5374.  public:
    5375. 

  5375.     backend0() : a0()
    5376. 

  5376.     {
    5377. 

  5377.     }
    5378. 

  5378. 

  5379.     T const&amp; get_a0() const
    5380. 

  5380.     {
    5381. 

  5381.         return this-&gt;a0;
    5382. 

  5382.     }
    5383. 

  5383. 

  5384.  protected:
    5385. 

  5385.     template &lt;typename ArgPack&gt;
    5386. 

  5386.     void initialize_impl(ArgPack const&amp; args)
    5387. 

  5387.     {
    5388. 

  5388.         this-&gt;a0 = args[_a0];
    5389. 

  5389.     }
    5390. 

  5390. };
    5391. 

  5391. 

  5392. template &lt;typename B, typename T&gt;
    5393. 

  5393. class backend1 : public B
    5394. 

  5394. {
    5395. 

  5395.     T a1;
    5396. 

  5396. 

  5397.  public:
    5398. 

  5398.     backend1() : B(), a1()
    5399. 

  5399.     {
    5400. 

  5400.     }
    5401. 

  5401. 

  5402.     T const&amp; get_a1() const
    5403. 

  5403.     {
    5404. 

  5404.         return this-&gt;a1;
    5405. 

  5405.     }
    5406. 

  5406. 

  5407.  protected:
    5408. 

  5408.     template &lt;typename ArgPack&gt;
    5409. 

  5409.     void initialize_impl(ArgPack const&amp; args)
    5410. 

  5410.     {
    5411. 

  5411.         B::initialize_impl(args);
    5412. 

  5412.         this-&gt;a1 = args[_a1];
    5413. 

  5413.     }
    5414. 

  5414. };
    5415. 

  5415. 

  5416. template &lt;typename B, typename T&gt;
    5417. 

  5417. class backend2 : public B
    5418. 

  5418. {
    5419. 

  5419.     T a2;
    5420. 

  5420. 

  5421.  public:
    5422. 

  5422.     backend2() : B(), a2()
    5423. 

  5423.     {
    5424. 

  5424.     }
    5425. 

  5425. 

  5426.     T const&amp; get_a2() const
    5427. 

  5427.     {
    5428. 

  5428.         return this-&gt;a2;
    5429. 

  5429.     }
    5430. 

  5430. 

  5431.  protected:
    5432. 

  5432.     template &lt;typename ArgPack&gt;
    5433. 

  5433.     void initialize_impl(ArgPack const&amp; args)
    5434. 

  5434.     {
    5435. 

  5435.         B::initialize_impl(args);
    5436. 

  5436.         this-&gt;a2 = args[_a2];
    5437. 

  5437.     }
    5438. 

  5438. };
    5439. 

  5439. </pre>
    5440. 

  5440. <p>This example shows that while <tt class="docutils literal">backend0</tt> must always be the root base class
    5441. 

  5441. template and that <tt class="docutils literal">frontend</tt> must always be the most derived class template,
    5442. 

  5442. the other back-ends can be chained together in different orders.</p>
    5443. 

  5443. <pre class="literal-block">
    5444. 

  5444. char const* p = &quot;foo&quot;;
    5445. 

  5445. frontend&lt;
    5446. 

  5446.     backend2&lt;backend1&lt;backend0&lt;char const*&gt;, char&gt;, int&gt;
    5447. 

  5447. &gt; composed_obj0;
    5448. 

  5448. frontend&lt;
    5449. 

  5449.     backend1&lt;backend2&lt;backend0&lt;char const*&gt;, int&gt;, char&gt;
    5450. 

  5450. &gt; composed_obj1;
    5451. 

  5451. composed_obj0.initialize(_a2 = 4, _a1 = ' ', _a0 = p);
    5452. 

  5452. composed_obj1.initialize(_a0 = p, _a1 = ' ', _a2 = 4);
    5453. 

  5453. BOOST_TEST_EQ(composed_obj0.get_a0(), composed_obj1.get_a0());
    5454. 

  5454. BOOST_TEST_EQ(composed_obj0.get_a1(), composed_obj1.get_a1());
    5455. 

  5455. BOOST_TEST_EQ(composed_obj0.get_a2(), composed_obj1.get_a2());
    5456. 

  5456. </pre>
    5457. 

  5457. <p>The <a class="reference external" href="../../test/parameterized_inheritance.cpp">parameterized_inheritance.cpp</a> and <a class="reference external" href="../../test/preprocessor_eval_cat_no_spec.cpp">preprocessor_eval_cat_no_spec.cpp</a> test
    5458. 

  5458. programs demonstrate proper usage of this macro.</p>
    5459. 

  5459. <p><strong>Macro parameters:</strong></p>
    5460. 

  5460. <ul class="simple">
    5461. 

  5461. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    5462. 

  5462. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    5463. 

  5463. generated implementation function.  <tt class="docutils literal">name</tt> may be qualified by the
    5464. 

  5464. <tt class="docutils literal">static</tt> keyword to declare the member function and its helpers as not
    5465. 

  5465. associated with any object of the enclosing type.</li>
    5466. 

  5466. </ul>
    5467. 

  5467. <p><strong>Argument specifiers syntax:</strong></p>
    5468. 

  5468. <p>None.</p>
    5469. 

  5469. <p><strong>Approximate expansion:</strong></p>
    5470. 

  5470. <pre class="literal-block">
    5471. 

  5471. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    5472. 

  5472. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    5473. 

  5473. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    5474. 

  5474. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    5475. 

  5475. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    5476. 

  5476. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5477. 

  5477. using boost_param_no_spec_result_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    5478. 

  5478. 

  5479. // If <strong>result</strong> is a simple return type:
    5480. 

  5480. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5481. 

  5481. struct boost_param_no_spec_result_ ## __LINE__ ## <strong>name</strong>
    5482. 

  5482. {
    5483. 

  5483.     typedef <strong>result</strong> type;
    5484. 

  5484. };
    5485. 

  5485. 

  5486. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5487. 

  5487. inline typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>&lt;
    5488. 

  5488.     <a class="reference internal" href="#are-tagged-arguments"><tt class="docutils literal">are_tagged_arguments</tt></a>&lt;TaggedArg0,TaggedArgs...&gt;
    5489. 

  5489.   , boost_param_no_spec_result_ ## __LINE__ ## <strong>name</strong>&lt;
    5490. 

  5490.         TaggedArg0
    5491. 

  5491.       , TaggedArgs...
    5492. 

  5492.     &gt;
    5493. 

  5493. &gt;::type
    5494. 

  5494.     <strong>name</strong>(TaggedArg0 const&amp; arg0, TaggedArgs const&amp;... args)
    5495. 

  5495. {
    5496. 

  5496.     return this-&gt;boost_param_no_spec_impl ## __LINE__ ## <strong>name</strong>(
    5497. 

  5497.         static_cast&lt;
    5498. 

  5498.             typename
    5499. 

  5499.             boost_param_no_spec_result_ ## __LINE__ ## <strong>name</strong>&lt;
    5500. 

  5500.                 TaggedArg0
    5501. 

  5501.               , TaggedArgs...
    5502. 

  5502.             &gt;::type(*)()
    5503. 

  5503.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    5504. 

  5504.       , <a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a>(arg0, args...)
    5505. 

  5505.     );
    5506. 

  5506. }
    5507. 

  5507. 

  5508. template &lt;typename ResultType, typename Args&gt;
    5509. 

  5509. ResultType
    5510. 

  5510.     boost_param_no_spec_impl ## __LINE__ ## <strong>name</strong>(
    5511. 

  5511.         (ResultType(*)())
    5512. 

  5512.       , Args const&amp; args
    5513. 

  5513.     )
    5514. 

  5514. </pre>
    5515. 

  5515. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    5516. 

  5516. available for use within the function body.</p>
    5517. 

  5517. </div>
    5518. 

  5518. <div class="section" id="boost-parameter-no-spec-const-member-function-result-name">
    5519. 

  5519. <span id="boost-parameter-no-spec-const-member-function"></span><h2><a class="toc-backref" href="#id70">7.14&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION(result, name)</tt></a></h2>
    5520. 

  5520. <table class="docutils field-list" frame="void" rules="none">
    5521. 

  5521. <col class="field-name" />
    5522. 

  5522. <col class="field-body" />
    5523. 

  5523. <tbody valign="top">
    5524. 

  5524. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor_no_spec.hpp">boost/parameter/preprocessor_no_spec.hpp</a></td>
    5525. 

  5525. </tr>
    5526. 

  5526. </tbody>
    5527. 

  5527. </table>
    5528. 

  5528. <p>Generates a member function that can take in named arguments.</p>
    5529. 

  5529. <table class="docutils field-list" frame="void" rules="none">
    5530. 

  5530. <col class="field-name" />
    5531. 

  5531. <col class="field-body" />
    5532. 

  5532. <tbody valign="top">
    5533. 

  5533. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    5534. 

  5534. </tr>
    5535. 

  5535. </tbody>
    5536. 

  5536. </table>
    5537. 

  5537. <p>The return type of each of the following function templates falls under a
    5538. 

  5538. different value category.</p>
    5539. 

  5539. <pre class="literal-block">
    5540. 

  5540. template &lt;std::size_t N&gt;
    5541. 

  5541. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    5542. 

  5542. {
    5543. 

  5543.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5544. 

  5544. }
    5545. 

  5545. 

  5546. template &lt;std::size_t N&gt;
    5547. 

  5547. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    5548. 

  5548. {
    5549. 

  5549.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5550. 

  5550. }
    5551. 

  5551. 

  5552. template &lt;std::size_t N&gt;
    5553. 

  5553. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    5554. 

  5554. {
    5555. 

  5555.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5556. 

  5556.     return lset;
    5557. 

  5557. }
    5558. 

  5558. 

  5559. template &lt;std::size_t N&gt;
    5560. 

  5560. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    5561. 

  5561. {
    5562. 

  5562.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5563. 

  5563.     return clset;
    5564. 

  5564. }
    5565. 

  5565. </pre>
    5566. 

  5566. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    5567. 

  5567. to return the correct value category when passed in an object returned by one
    5568. 

  5568. of the functions defined above.  Assume that
    5569. 

  5569. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    5570. 

  5570. <pre class="literal-block">
    5571. 

  5571. enum invoked
    5572. 

  5572. {
    5573. 

  5573.     passed_by_lvalue_reference_to_const
    5574. 

  5574.   , passed_by_lvalue_reference
    5575. 

  5575.   , passed_by_rvalue_reference_to_const
    5576. 

  5576.   , passed_by_rvalue_reference
    5577. 

  5577. };
    5578. 

  5578. 

  5579. struct U
    5580. 

  5580. {
    5581. 

  5581.     template &lt;std::size_t N&gt;
    5582. 

  5582.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    5583. 

  5583.     {
    5584. 

  5584.         return passed_by_lvalue_reference_to_const;
    5585. 

  5585.     }
    5586. 

  5586. 

  5587.     template &lt;std::size_t N&gt;
    5588. 

  5588.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    5589. 

  5589.     {
    5590. 

  5590.         return passed_by_lvalue_reference;
    5591. 

  5591.     }
    5592. 

  5592. 

  5593.     template &lt;std::size_t N&gt;
    5594. 

  5594.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    5595. 

  5595.     {
    5596. 

  5596.         return passed_by_rvalue_reference_to_const;
    5597. 

  5597.     }
    5598. 

  5598. 

  5599.     template &lt;std::size_t N&gt;
    5600. 

  5600.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    5601. 

  5601.     {
    5602. 

  5602.         return passed_by_rvalue_reference;
    5603. 

  5603.     }
    5604. 

  5604. };
    5605. 

  5605. </pre>
    5606. 

  5606. <p>Named parameters are required when invoking the member function; however, none
    5607. 

  5607. of their tags need to be in the same namespace.</p>
    5608. 

  5608. <pre class="literal-block">
    5609. 

  5609. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw0) in(lrc))
    5610. 

  5610. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw1) in_out(lr))
    5611. 

  5611. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw2) in(rrc))
    5612. 

  5612. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw3) consume(rr))
    5613. 

  5613. </pre>
    5614. 

  5614. <p>Use the macro as a substitute for a variadic function header.  Enclose the
    5615. 

  5615. return type <tt class="docutils literal">bool</tt> in parentheses.  The macro will qualify the function with
    5616. 

  5616. the <tt class="docutils literal">const</tt> keyword.</p>
    5617. 

  5617. <pre class="literal-block">
    5618. 

  5618. struct D
    5619. 

  5619. {
    5620. 

  5620.     D()
    5621. 

  5621.     {
    5622. 

  5622.     }
    5623. 

  5623. 

  5624.     BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION((bool), evaluate_m)
    5625. 

  5625.     {
    5626. 

  5626.         BOOST_TEST_EQ(
    5627. 

  5627.             passed_by_lvalue_reference_to_const
    5628. 

  5628.           , U::evaluate_category&lt;0&gt;(args[_lrc])
    5629. 

  5629.         );
    5630. 

  5630.         BOOST_TEST_EQ(
    5631. 

  5631.             passed_by_lvalue_reference
    5632. 

  5632.           , U::evaluate_category&lt;1&gt;(args[_lr])
    5633. 

  5633.         );
    5634. 

  5634.         BOOST_TEST_EQ(
    5635. 

  5635.             passed_by_rvalue_reference_to_const
    5636. 

  5636.           , U::evaluate_category&lt;2&gt;(
    5637. 

  5637.                 args[_rrc | rvalue_const_bitset&lt;2&gt;()]
    5638. 

  5638.             )
    5639. 

  5639.         );
    5640. 

  5640.         BOOST_TEST_EQ(
    5641. 

  5641.             passed_by_rvalue_reference
    5642. 

  5642.           , U::evaluate_category&lt;3&gt;(
    5643. 

  5643.                 args[_rr | rvalue_bitset&lt;3&gt;()]
    5644. 

  5644.             )
    5645. 

  5645.         );
    5646. 

  5646. 

  5647.         return true;
    5648. 

  5648.     }
    5649. 

  5649. };
    5650. 

  5650. </pre>
    5651. 

  5651. <p>To invoke the member function, bind all its arguments to named parameters.</p>
    5652. 

  5652. <pre class="literal-block">
    5653. 

  5653. D const d = D();
    5654. 

  5654. d.evaluate_m(
    5655. 

  5655.     _rr0 = rvalue_bitset&lt;3&gt;()
    5656. 

  5656.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    5657. 

  5657.   , _lr0 = lvalue_bitset&lt;1&gt;()
    5658. 

  5658.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    5659. 

  5659. );
    5660. 

  5660. d.evaluate_m(
    5661. 

  5661.     _lr0 = lvalue_bitset&lt;1&gt;()
    5662. 

  5662.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    5663. 

  5663. );
    5664. 

  5664. </pre>
    5665. 

  5665. <p>The <a class="reference external" href="../../test/preprocessor_eval_cat_no_spec.cpp">preprocessor_eval_cat_no_spec.cpp</a> test program demonstrates proper usage of
    5666. 

  5666. this macro.</p>
    5667. 

  5667. <p><strong>Macro parameters:</strong></p>
    5668. 

  5668. <ul class="simple">
    5669. 

  5669. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function.</li>
    5670. 

  5670. <li><tt class="docutils literal">name</tt> is the base name of the function; it determines the name of the
    5671. 

  5671. generated implementation function.</li>
    5672. 

  5672. </ul>
    5673. 

  5673. <p><strong>Argument specifiers syntax:</strong></p>
    5674. 

  5674. <p>None.</p>
    5675. 

  5675. <p><strong>Approximate expansion:</strong></p>
    5676. 

  5676. <pre class="literal-block">
    5677. 

  5677. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    5678. 

  5678. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    5679. 

  5679. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    5680. 

  5680. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    5681. 

  5681. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    5682. 

  5682. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5683. 

  5683. using boost_param_no_spec_result_const_ ## __LINE__ ## <strong>name</strong> = <strong>result</strong>;
    5684. 

  5684. 

  5685. // If <strong>result</strong> is a simple return type:
    5686. 

  5686. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5687. 

  5687. struct boost_param_no_spec_result_const_ ## __LINE__ ## <strong>name</strong>
    5688. 

  5688. {
    5689. 

  5689.     typedef <strong>result</strong> type;
    5690. 

  5690. };
    5691. 

  5691. 

  5692. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5693. 

  5693. inline typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>&lt;
    5694. 

  5694.     <a class="reference internal" href="#are-tagged-arguments"><tt class="docutils literal">are_tagged_arguments</tt></a>&lt;TaggedArg0,TaggedArgs...&gt;
    5695. 

  5695.   , boost_param_no_spec_result_const_ ## __LINE__ ## <strong>name</strong>&lt;
    5696. 

  5696.         TaggedArg0
    5697. 

  5697.       , TaggedArgs...
    5698. 

  5698.     &gt;
    5699. 

  5699. &gt;::type
    5700. 

  5700.     <strong>name</strong>(TaggedArg0 const&amp; arg0, TaggedArgs const&amp;... args) const
    5701. 

  5701. {
    5702. 

  5702.     return this-&gt;boost_param_no_spec_impl_const ## __LINE__ ## <strong>name</strong>(
    5703. 

  5703.         static_cast&lt;
    5704. 

  5704.             typename
    5705. 

  5705.             boost_param_no_spec_result_const_ ## __LINE__ ## <strong>name</strong>&lt;
    5706. 

  5706.                 TaggedArg0
    5707. 

  5707.               , TaggedArgs...
    5708. 

  5708.             &gt;::type(*)()
    5709. 

  5709.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    5710. 

  5710.       , <a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a>(arg0, args...)
    5711. 

  5711.     );
    5712. 

  5712. }
    5713. 

  5713. 

  5714. template &lt;typename ResultType, typename Args&gt;
    5715. 

  5715. ResultType
    5716. 

  5716.     boost_param_no_spec_impl_const ## __LINE__ ## <strong>name</strong>(
    5717. 

  5717.         (ResultType(*)())
    5718. 

  5718.       , Args const&amp; args
    5719. 

  5719.     ) const
    5720. 

  5720. </pre>
    5721. 

  5721. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    5722. 

  5722. available for use within the function body.</p>
    5723. 

  5723. </div>
    5724. 

  5724. <div class="section" id="boost-parameter-no-spec-function-call-operator-result">
    5725. 

  5725. <span id="boost-parameter-no-spec-function-call-operator"></span><h2><a class="toc-backref" href="#id71">7.15&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR(result)</tt></a></h2>
    5726. 

  5726. <table class="docutils field-list" frame="void" rules="none">
    5727. 

  5727. <col class="field-name" />
    5728. 

  5728. <col class="field-body" />
    5729. 

  5729. <tbody valign="top">
    5730. 

  5730. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor_no_spec.hpp">boost/parameter/preprocessor_no_spec.hpp</a></td>
    5731. 

  5731. </tr>
    5732. 

  5732. </tbody>
    5733. 

  5733. </table>
    5734. 

  5734. <p>Generates a function call operator that can take in named arguments.</p>
    5735. 

  5735. <table class="docutils field-list" frame="void" rules="none">
    5736. 

  5736. <col class="field-name" />
    5737. 

  5737. <col class="field-body" />
    5738. 

  5738. <tbody valign="top">
    5739. 

  5739. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    5740. 

  5740. </tr>
    5741. 

  5741. </tbody>
    5742. 

  5742. </table>
    5743. 

  5743. <p>When designing a front-end class template whose back-end is configurable via
    5744. 

  5744. parameterized inheritance, it can be useful to omit argument specifiers from
    5745. 

  5745. a named-parameter function call operator so that the delegate member functions
    5746. 

  5746. of the back-end classes can enforce their own specifications.</p>
    5747. 

  5747. <pre class="literal-block">
    5748. 

  5748. template &lt;typename B&gt;
    5749. 

  5749. struct frontend : B
    5750. 

  5750. {
    5751. 

  5751.     frontend() : B()
    5752. 

  5752.     {
    5753. 

  5753.     }
    5754. 

  5754. 

  5755.     BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR((void))
    5756. 

  5756.     {
    5757. 

  5757.         this-&gt;initialize_impl(args);
    5758. 

  5758.     }
    5759. 

  5759. };
    5760. 

  5760. </pre>
    5761. 

  5761. <p>Named parameters are required when invoking the function call operator;
    5762. 

  5762. however, none of their tags need to be in the same namespace.</p>
    5763. 

  5763. <pre class="literal-block">
    5764. 

  5764. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a0)
    5765. 

  5765. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a1)
    5766. 

  5766. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a2)
    5767. 

  5767. </pre>
    5768. 

  5768. <p>For this example, each of the back-end class templates requires its own
    5769. 

  5769. parameter to be present in the argument pack.  In practice, such parameters
    5770. 

  5770. should be optional, with default values.</p>
    5771. 

  5771. <pre class="literal-block">
    5772. 

  5772. template &lt;typename T&gt;
    5773. 

  5773. class backend0
    5774. 

  5774. {
    5775. 

  5775.     T a0;
    5776. 

  5776. 

  5777.  public:
    5778. 

  5778.     backend0() : a0()
    5779. 

  5779.     {
    5780. 

  5780.     }
    5781. 

  5781. 

  5782.     T const&amp; get_a0() const
    5783. 

  5783.     {
    5784. 

  5784.         return this-&gt;a0;
    5785. 

  5785.     }
    5786. 

  5786. 

  5787.  protected:
    5788. 

  5788.     template &lt;typename ArgPack&gt;
    5789. 

  5789.     void initialize_impl(ArgPack const&amp; args)
    5790. 

  5790.     {
    5791. 

  5791.         this-&gt;a0 = args[_a0];
    5792. 

  5792.     }
    5793. 

  5793. };
    5794. 

  5794. 

  5795. template &lt;typename B, typename T&gt;
    5796. 

  5796. class backend1 : public B
    5797. 

  5797. {
    5798. 

  5798.     T a1;
    5799. 

  5799. 

  5800.  public:
    5801. 

  5801.     backend1() : B(), a1()
    5802. 

  5802.     {
    5803. 

  5803.     }
    5804. 

  5804. 

  5805.     T const&amp; get_a1() const
    5806. 

  5806.     {
    5807. 

  5807.         return this-&gt;a1;
    5808. 

  5808.     }
    5809. 

  5809. 

  5810.  protected:
    5811. 

  5811.     template &lt;typename ArgPack&gt;
    5812. 

  5812.     void initialize_impl(ArgPack const&amp; args)
    5813. 

  5813.     {
    5814. 

  5814.         B::initialize_impl(args);
    5815. 

  5815.         this-&gt;a1 = args[_a1];
    5816. 

  5816.     }
    5817. 

  5817. };
    5818. 

  5818. 

  5819. template &lt;typename B, typename T&gt;
    5820. 

  5820. class backend2 : public B
    5821. 

  5821. {
    5822. 

  5822.     T a2;
    5823. 

  5823. 

  5824.  public:
    5825. 

  5825.     backend2() : B(), a2()
    5826. 

  5826.     {
    5827. 

  5827.     }
    5828. 

  5828. 

  5829.     T const&amp; get_a2() const
    5830. 

  5830.     {
    5831. 

  5831.         return this-&gt;a2;
    5832. 

  5832.     }
    5833. 

  5833. 

  5834.  protected:
    5835. 

  5835.     template &lt;typename ArgPack&gt;
    5836. 

  5836.     void initialize_impl(ArgPack const&amp; args)
    5837. 

  5837.     {
    5838. 

  5838.         B::initialize_impl(args);
    5839. 

  5839.         this-&gt;a2 = args[_a2];
    5840. 

  5840.     }
    5841. 

  5841. };
    5842. 

  5842. </pre>
    5843. 

  5843. <p>This example shows that while <tt class="docutils literal">backend0</tt> must always be the root base class
    5844. 

  5844. template and that <tt class="docutils literal">frontend</tt> must always be the most derived class template,
    5845. 

  5845. the other back-ends can be chained together in different orders.</p>
    5846. 

  5846. <pre class="literal-block">
    5847. 

  5847. char const* p = &quot;foo&quot;;
    5848. 

  5848. frontend&lt;
    5849. 

  5849.     backend2&lt;backend1&lt;backend0&lt;char const*&gt;, char&gt;, int&gt;
    5850. 

  5850. &gt; composed_obj0;
    5851. 

  5851. frontend&lt;
    5852. 

  5852.     backend1&lt;backend2&lt;backend0&lt;char const*&gt;, int&gt;, char&gt;
    5853. 

  5853. &gt; composed_obj1;
    5854. 

  5854. composed_obj0(_a2 = 4, _a1 = ' ', _a0 = p);
    5855. 

  5855. composed_obj1(_a0 = p, _a1 = ' ', _a2 = 4);
    5856. 

  5856. BOOST_TEST_EQ(composed_obj0.get_a0(), composed_obj1.get_a0());
    5857. 

  5857. BOOST_TEST_EQ(composed_obj0.get_a1(), composed_obj1.get_a1());
    5858. 

  5858. BOOST_TEST_EQ(composed_obj0.get_a2(), composed_obj1.get_a2());
    5859. 

  5859. </pre>
    5860. 

  5860. <p>The <a class="reference external" href="../../test/parameterized_inheritance.cpp">parameterized_inheritance.cpp</a> and <a class="reference external" href="../../test/preprocessor_eval_cat_no_spec.cpp">preprocessor_eval_cat_no_spec.cpp</a> test
    5861. 

  5861. programs demonstrate proper usage of this macro.</p>
    5862. 

  5862. <p><strong>Macro parameters:</strong></p>
    5863. 

  5863. <ul class="simple">
    5864. 

  5864. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function call operator.</li>
    5865. 

  5865. </ul>
    5866. 

  5866. <p><strong>Argument specifiers syntax:</strong></p>
    5867. 

  5867. <p>None.</p>
    5868. 

  5868. <p><strong>Approximate expansion:</strong></p>
    5869. 

  5869. <pre class="literal-block">
    5870. 

  5870. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    5871. 

  5871. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    5872. 

  5872. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    5873. 

  5873. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    5874. 

  5874. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    5875. 

  5875. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5876. 

  5876. using boost_param_no_spec_result_ ## __LINE__ ## operator = <strong>result</strong>;
    5877. 

  5877. 

  5878. // If <strong>result</strong> is a simple return type:
    5879. 

  5879. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5880. 

  5880. struct boost_param_no_spec_result_ ## __LINE__ ## operator
    5881. 

  5881. {
    5882. 

  5882.     typedef <strong>result</strong> type;
    5883. 

  5883. };
    5884. 

  5884. 

  5885. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    5886. 

  5886. inline typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>&lt;
    5887. 

  5887.     <a class="reference internal" href="#are-tagged-arguments"><tt class="docutils literal">are_tagged_arguments</tt></a>&lt;TaggedArg0,TaggedArgs...&gt;
    5888. 

  5888.   , boost_param_no_spec_result_ ## __LINE__ ## operator&lt;
    5889. 

  5889.         TaggedArg0
    5890. 

  5890.       , TaggedArgs...
    5891. 

  5891.     &gt;
    5892. 

  5892. &gt;::type
    5893. 

  5893.     operator()(TaggedArg0 const&amp; arg0, TaggedArgs const&amp;... args)
    5894. 

  5894. {
    5895. 

  5895.     return this-&gt;boost_param_no_spec_impl ## __LINE__ ## operator(
    5896. 

  5896.         static_cast&lt;
    5897. 

  5897.             typename
    5898. 

  5898.             boost_param_no_spec_result_ ## __LINE__ ## operator&lt;
    5899. 

  5899.                 TaggedArg0
    5900. 

  5900.               , TaggedArgs...
    5901. 

  5901.             &gt;::type(*)()
    5902. 

  5902.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    5903. 

  5903.       , <a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a>(arg0, args...)
    5904. 

  5904.     );
    5905. 

  5905. }
    5906. 

  5906. 

  5907. template &lt;typename ResultType, typename Args&gt;
    5908. 

  5908. ResultType
    5909. 

  5909.     boost_param_no_spec_impl ## __LINE__ ## operator(
    5910. 

  5910.         (ResultType(*)())
    5911. 

  5911.       , Args const&amp; args
    5912. 

  5912.     )
    5913. 

  5913. </pre>
    5914. 

  5914. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    5915. 

  5915. available for use within the function body.</p>
    5916. 

  5916. </div>
    5917. 

  5917. <div class="section" id="boost-parameter-no-spec-const-function-call-operator-result">
    5918. 

  5918. <span id="boost-parameter-no-spec-const-function-call-operator"></span><h2><a class="toc-backref" href="#id72">7.16&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR(result)</tt></a></h2>
    5919. 

  5919. <table class="docutils field-list" frame="void" rules="none">
    5920. 

  5920. <col class="field-name" />
    5921. 

  5921. <col class="field-body" />
    5922. 

  5922. <tbody valign="top">
    5923. 

  5923. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor_no_spec.hpp">boost/parameter/preprocessor_no_spec.hpp</a></td>
    5924. 

  5924. </tr>
    5925. 

  5925. </tbody>
    5926. 

  5926. </table>
    5927. 

  5927. <p>Generates a function call operator that can take in named arguments.</p>
    5928. 

  5928. <table class="docutils field-list" frame="void" rules="none">
    5929. 

  5929. <col class="field-name" />
    5930. 

  5930. <col class="field-body" />
    5931. 

  5931. <tbody valign="top">
    5932. 

  5932. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    5933. 

  5933. </tr>
    5934. 

  5934. </tbody>
    5935. 

  5935. </table>
    5936. 

  5936. <p>The return type of each of the following function templates falls under a
    5937. 

  5937. different value category.</p>
    5938. 

  5938. <pre class="literal-block">
    5939. 

  5939. template &lt;std::size_t N&gt;
    5940. 

  5940. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    5941. 

  5941. {
    5942. 

  5942.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5943. 

  5943. }
    5944. 

  5944. 

  5945. template &lt;std::size_t N&gt;
    5946. 

  5946. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    5947. 

  5947. {
    5948. 

  5948.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5949. 

  5949. }
    5950. 

  5950. 

  5951. template &lt;std::size_t N&gt;
    5952. 

  5952. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    5953. 

  5953. {
    5954. 

  5954.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5955. 

  5955.     return lset;
    5956. 

  5956. }
    5957. 

  5957. 

  5958. template &lt;std::size_t N&gt;
    5959. 

  5959. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    5960. 

  5960. {
    5961. 

  5961.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    5962. 

  5962.     return clset;
    5963. 

  5963. }
    5964. 

  5964. </pre>
    5965. 

  5965. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    5966. 

  5966. to return the correct value category when passed in an object returned by one
    5967. 

  5967. of the functions defined above.  Assume that
    5968. 

  5968. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    5969. 

  5969. <pre class="literal-block">
    5970. 

  5970. enum invoked
    5971. 

  5971. {
    5972. 

  5972.     passed_by_lvalue_reference_to_const
    5973. 

  5973.   , passed_by_lvalue_reference
    5974. 

  5974.   , passed_by_rvalue_reference_to_const
    5975. 

  5975.   , passed_by_rvalue_reference
    5976. 

  5976. };
    5977. 

  5977. 

  5978. struct U
    5979. 

  5979. {
    5980. 

  5980.     template &lt;std::size_t N&gt;
    5981. 

  5981.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    5982. 

  5982.     {
    5983. 

  5983.         return passed_by_lvalue_reference_to_const;
    5984. 

  5984.     }
    5985. 

  5985. 

  5986.     template &lt;std::size_t N&gt;
    5987. 

  5987.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    5988. 

  5988.     {
    5989. 

  5989.         return passed_by_lvalue_reference;
    5990. 

  5990.     }
    5991. 

  5991. 

  5992.     template &lt;std::size_t N&gt;
    5993. 

  5993.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    5994. 

  5994.     {
    5995. 

  5995.         return passed_by_rvalue_reference_to_const;
    5996. 

  5996.     }
    5997. 

  5997. 

  5998.     template &lt;std::size_t N&gt;
    5999. 

  5999.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    6000. 

  6000.     {
    6001. 

  6001.         return passed_by_rvalue_reference;
    6002. 

  6002.     }
    6003. 

  6003. };
    6004. 

  6004. </pre>
    6005. 

  6005. <p>Named parameters are required when invoking the function call operator;
    6006. 

  6006. however, none of their tags need to be in the same namespace.</p>
    6007. 

  6007. <pre class="literal-block">
    6008. 

  6008. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw0) in(lrc))
    6009. 

  6009. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw1) in_out(lr))
    6010. 

  6010. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw2) in(rrc))
    6011. 

  6011. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw3) consume(rr))
    6012. 

  6012. </pre>
    6013. 

  6013. <p>Use the macro as a substitute for a variadic function call operator
    6014. 

  6014. header.  Enclose the return type <tt class="docutils literal">bool</tt> in parentheses.  The macro will
    6015. 

  6015. qualify the function with the <tt class="docutils literal">const</tt> keyword.</p>
    6016. 

  6016. <pre class="literal-block">
    6017. 

  6017. struct D
    6018. 

  6018. {
    6019. 

  6019.     D()
    6020. 

  6020.     {
    6021. 

  6021.     }
    6022. 

  6022. 

  6023.     BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR((bool))
    6024. 

  6024.     {
    6025. 

  6025.         BOOST_TEST_EQ(
    6026. 

  6026.             passed_by_lvalue_reference_to_const
    6027. 

  6027.           , U::evaluate_category&lt;0&gt;(args[_lrc])
    6028. 

  6028.         );
    6029. 

  6029.         BOOST_TEST_EQ(
    6030. 

  6030.             passed_by_lvalue_reference
    6031. 

  6031.           , U::evaluate_category&lt;1&gt;(args[_lr])
    6032. 

  6032.         );
    6033. 

  6033.         BOOST_TEST_EQ(
    6034. 

  6034.             passed_by_rvalue_reference_to_const
    6035. 

  6035.           , U::evaluate_category&lt;2&gt;(
    6036. 

  6036.                 args[_rrc | rvalue_const_bitset&lt;2&gt;()]
    6037. 

  6037.             )
    6038. 

  6038.         );
    6039. 

  6039.         BOOST_TEST_EQ(
    6040. 

  6040.             passed_by_rvalue_reference
    6041. 

  6041.           , U::evaluate_category&lt;3&gt;(
    6042. 

  6042.                 args[_rr | rvalue_bitset&lt;3&gt;()]
    6043. 

  6043.             )
    6044. 

  6044.         );
    6045. 

  6045. 

  6046.         return true;
    6047. 

  6047.     }
    6048. 

  6048. };
    6049. 

  6049. </pre>
    6050. 

  6050. <p>To invoke the function call operator, bind all its arguments to named
    6051. 

  6051. parameters.</p>
    6052. 

  6052. <pre class="literal-block">
    6053. 

  6053. D const d = D();
    6054. 

  6054. d(
    6055. 

  6055.     _rr0 = rvalue_bitset&lt;3&gt;()
    6056. 

  6056.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    6057. 

  6057.   , _lr0 = lvalue_bitset&lt;1&gt;()
    6058. 

  6058.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    6059. 

  6059. );
    6060. 

  6060. d(
    6061. 

  6061.     _lr0 = lvalue_bitset&lt;1&gt;()
    6062. 

  6062.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    6063. 

  6063. );
    6064. 

  6064. </pre>
    6065. 

  6065. <p>The <a class="reference external" href="../../test/preprocessor_eval_cat_no_spec.cpp">preprocessor_eval_cat_no_spec.cpp</a> test program demonstrates proper usage of this
    6066. 

  6066. macro.</p>
    6067. 

  6067. <p><strong>Macro parameters:</strong></p>
    6068. 

  6068. <ul class="simple">
    6069. 

  6069. <li><tt class="docutils literal">result</tt> is the parenthesized return type of the function call operator.</li>
    6070. 

  6070. </ul>
    6071. 

  6071. <p><strong>Argument specifiers syntax:</strong></p>
    6072. 

  6072. <p>None.</p>
    6073. 

  6073. <p><strong>Approximate expansion:</strong></p>
    6074. 

  6074. <pre class="literal-block">
    6075. 

  6075. // If <strong>result</strong> is a template instantiation of <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>,
    6076. 

  6076. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>,
    6077. 

  6077. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if_c</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::disable_if_c</a>,
    6078. 

  6078. // <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if</a>, <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_disable_if_c</a>, or
    6079. 

  6079. // <a class="reference external" href="http://en.cppreference.com/w/cpp/types/enable_if">std::enable_if</a>:
    6080. 

  6080. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    6081. 

  6081. using boost_param_no_spec_result_const_ ## __LINE__ ## operator = <strong>result</strong>;
    6082. 

  6082. 

  6083. // If <strong>result</strong> is a simple return type:
    6084. 

  6084. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    6085. 

  6085. struct boost_param_no_spec_result_const_ ## __LINE__ ## operator
    6086. 

  6086. {
    6087. 

  6087.     typedef <strong>result</strong> type;
    6088. 

  6088. };
    6089. 

  6089. 

  6090. template &lt;typename TaggedArg0, typename ...TaggedArgs&gt;
    6091. 

  6091. inline typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::lazy_enable_if</a>&lt;
    6092. 

  6092.     <a class="reference internal" href="#are-tagged-arguments"><tt class="docutils literal">are_tagged_arguments</tt></a>&lt;TaggedArg0,TaggedArgs...&gt;
    6093. 

  6093.   , boost_param_no_spec_result_const_ ## __LINE__ ## operator&lt;
    6094. 

  6094.         TaggedArg0
    6095. 

  6095.       , TaggedArgs...
    6096. 

  6096.     &gt;
    6097. 

  6097. &gt;::type
    6098. 

  6098.     operator()(
    6099. 

  6099.         TaggedArg0 const&amp; arg0
    6100. 

  6100.       , TaggedArgs const&amp;... args
    6101. 

  6101.     ) const
    6102. 

  6102. {
    6103. 

  6103.     return this-&gt;boost_param_no_spec_impl_const ## __LINE__ ## operator(
    6104. 

  6104.         static_cast&lt;
    6105. 

  6105.             typename
    6106. 

  6106.             boost_param_no_spec_result_const_ ## __LINE__ ## operator&lt;
    6107. 

  6107.                 TaggedArg0
    6108. 

  6108.               , TaggedArgs...
    6109. 

  6109.             &gt;::type(*)()
    6110. 

  6110.         &gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    6111. 

  6111.       , <a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a>(arg0, args...)
    6112. 

  6112.     );
    6113. 

  6113. }
    6114. 

  6114. 

  6115. template &lt;typename ResultType, typename Args&gt;
    6116. 

  6116. ResultType
    6117. 

  6117.     boost_param_no_spec_impl_const ## __LINE__ ## operator(
    6118. 

  6118.         (ResultType(*)())
    6119. 

  6119.       , Args const&amp; args
    6120. 

  6120.     ) const
    6121. 

  6121. </pre>
    6122. 

  6122. <p>Only the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> type <tt class="docutils literal">Args</tt> and its object instance <tt class="docutils literal">args</tt> are
    6123. 

  6123. available for use within the function body.</p>
    6124. 

  6124. </div>
    6125. 

  6125. <div class="section" id="boost-parameter-no-spec-constructor-cls-impl">
    6126. 

  6126. <span id="boost-parameter-no-spec-constructor"></span><h2><a class="toc-backref" href="#id73">7.17&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR(cls, impl)</tt></a></h2>
    6127. 

  6127. <table class="docutils field-list" frame="void" rules="none">
    6128. 

  6128. <col class="field-name" />
    6129. 

  6129. <col class="field-body" />
    6130. 

  6130. <tbody valign="top">
    6131. 

  6131. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor_no_spec.hpp">boost/parameter/preprocessor_no_spec.hpp</a></td>
    6132. 

  6132. </tr>
    6133. 

  6133. </tbody>
    6134. 

  6134. </table>
    6135. 

  6135. <p>Generates a constructor that can take in named arguments.</p>
    6136. 

  6136. <table class="docutils field-list" frame="void" rules="none">
    6137. 

  6137. <col class="field-name" />
    6138. 

  6138. <col class="field-body" />
    6139. 

  6139. <tbody valign="top">
    6140. 

  6140. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    6141. 

  6141. </tr>
    6142. 

  6142. </tbody>
    6143. 

  6143. </table>
    6144. 

  6144. <p>When designing a front-end class template whose back-end is configurable via
    6145. 

  6145. parameterized inheritance, it can be useful to omit argument specifiers from
    6146. 

  6146. a named-parameter constructor so that the delegate constructors of the
    6147. 

  6147. back-end classes can enforce their own specifications.</p>
    6148. 

  6148. <pre class="literal-block">
    6149. 

  6149. template &lt;typename B&gt;
    6150. 

  6150. struct frontend : B
    6151. 

  6151. {
    6152. 

  6152.     BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR(frontend, (B))
    6153. 

  6153. };
    6154. 

  6154. </pre>
    6155. 

  6155. <p>Named parameters are required when invoking the constructor; however, none of
    6156. 

  6156. their tags need to be in the same namespace.</p>
    6157. 

  6157. <pre class="literal-block">
    6158. 

  6158. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a0)
    6159. 

  6159. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a1)
    6160. 

  6160. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(a2)
    6161. 

  6161. </pre>
    6162. 

  6162. <p>For this example, each of the back-end class templates requires its own
    6163. 

  6163. parameter to be present in the argument pack.  In practice, such parameters
    6164. 

  6164. should be optional, with default values.</p>
    6165. 

  6165. <pre class="literal-block">
    6166. 

  6166. struct _enabler
    6167. 

  6167. {
    6168. 

  6168. };
    6169. 

  6169. 

  6170. template &lt;typename T&gt;
    6171. 

  6171. class backend0
    6172. 

  6172. {
    6173. 

  6173.     T a0;
    6174. 

  6174. 

  6175.  public:
    6176. 

  6176.     template &lt;typename ArgPack&gt;
    6177. 

  6177.     explicit backend0(
    6178. 

  6178.         ArgPack const&amp; args
    6179. 

  6179.       , typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    6180. 

  6180.             <a class="reference internal" href="#is-argument-pack"><tt class="docutils literal">is_argument_pack</tt></a>&lt;ArgPack&gt;
    6181. 

  6181.           , _enabler
    6182. 

  6182.         &gt;::type = _enabler()
    6183. 

  6183.     ) : a0(args[_a0])
    6184. 

  6184.     {
    6185. 

  6185.     }
    6186. 

  6186. 

  6187.     T const&amp; get_a0() const
    6188. 

  6188.     {
    6189. 

  6189.         return this-&gt;a0;
    6190. 

  6190.     }
    6191. 

  6191. };
    6192. 

  6192. 

  6193. template &lt;typename B, typename T&gt;
    6194. 

  6194. class backend1 : public B
    6195. 

  6195. {
    6196. 

  6196.     T a1;
    6197. 

  6197. 

  6198.  public:
    6199. 

  6199.     template &lt;typename ArgPack&gt;
    6200. 

  6200.     explicit backend1(
    6201. 

  6201.         ArgPack const&amp; args
    6202. 

  6202.       , typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    6203. 

  6203.             <a class="reference internal" href="#is-argument-pack"><tt class="docutils literal">is_argument_pack</tt></a>&lt;ArgPack&gt;
    6204. 

  6204.           , _enabler
    6205. 

  6205.         &gt;::type = _enabler()
    6206. 

  6206.     ) : B(args), a1(args[_a1])
    6207. 

  6207.     {
    6208. 

  6208.     }
    6209. 

  6209. 

  6210.     T const&amp; get_a1() const
    6211. 

  6211.     {
    6212. 

  6212.         return this-&gt;a1;
    6213. 

  6213.     }
    6214. 

  6214. };
    6215. 

  6215. 

  6216. template &lt;typename B, typename T&gt;
    6217. 

  6217. class backend2 : public B
    6218. 

  6218. {
    6219. 

  6219.     T a2;
    6220. 

  6220. 

  6221.  public:
    6222. 

  6222.     template &lt;typename ArgPack&gt;
    6223. 

  6223.     explicit backend2(
    6224. 

  6224.         ArgPack const&amp; args
    6225. 

  6225.       , typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    6226. 

  6226.             <a class="reference internal" href="#is-argument-pack"><tt class="docutils literal">is_argument_pack</tt></a>&lt;ArgPack&gt;
    6227. 

  6227.           , _enabler
    6228. 

  6228.         &gt;::type = _enabler()
    6229. 

  6229.     ) : B(args), a2(args[_a2])
    6230. 

  6230.     {
    6231. 

  6231.     }
    6232. 

  6232. 

  6233.     T const&amp; get_a2() const
    6234. 

  6234.     {
    6235. 

  6235.         return this-&gt;a2;
    6236. 

  6236.     }
    6237. 

  6237. };
    6238. 

  6238. </pre>
    6239. 

  6239. <p>This example shows that while <tt class="docutils literal">backend0</tt> must always be the root base class
    6240. 

  6240. template and that <tt class="docutils literal">frontend</tt> must always be the most derived class template,
    6241. 

  6241. the other back-ends can be chained together in different orders.</p>
    6242. 

  6242. <pre class="literal-block">
    6243. 

  6243. char const* p = &quot;foo&quot;;
    6244. 

  6244. frontend&lt;
    6245. 

  6245.     backend2&lt;backend1&lt;backend0&lt;char const*&gt;, char&gt;, int&gt;
    6246. 

  6246. &gt; composed_obj0(_a2 = 4, _a1 = ' ', _a0 = p);
    6247. 

  6247. frontend&lt;
    6248. 

  6248.     backend1&lt;backend2&lt;backend0&lt;char const*&gt;, int&gt;, char&gt;
    6249. 

  6249. &gt; composed_obj1(_a0 = p, _a1 = ' ', _a2 = 4);
    6250. 

  6250. BOOST_TEST_EQ(composed_obj0.get_a0(), composed_obj1.get_a0());
    6251. 

  6251. BOOST_TEST_EQ(composed_obj0.get_a1(), composed_obj1.get_a1());
    6252. 

  6252. BOOST_TEST_EQ(composed_obj0.get_a2(), composed_obj1.get_a2());
    6253. 

  6253. </pre>
    6254. 

  6254. <p>The <a class="reference external" href="../../test/parameterized_inheritance.cpp">parameterized_inheritance.cpp</a> and <a class="reference external" href="../../test/preprocessor_eval_cat_no_spec.cpp">preprocessor_eval_cat_no_spec.cpp</a> test
    6255. 

  6255. programs demonstrate proper usage of this macro.</p>
    6256. 

  6256. <p><strong>Macro parameters:</strong></p>
    6257. 

  6257. <ul class="simple">
    6258. 

  6258. <li><tt class="docutils literal">cls</tt> is the name of the enclosing class.</li>
    6259. 

  6259. <li><tt class="docutils literal">impl</tt> is the parenthesized implementation base class for <tt class="docutils literal">cls</tt>.</li>
    6260. 

  6260. </ul>
    6261. 

  6261. <p><strong>Argument specifiers syntax:</strong></p>
    6262. 

  6262. <p>None.</p>
    6263. 

  6263. <p><strong>Approximate expansion:</strong></p>
    6264. 

  6264. <pre class="literal-block">
    6265. 

  6265. template &lt;
    6266. 

  6266.     typename TaggedArg0
    6267. 

  6267.   , typename ...TaggedArgs
    6268. 

  6268.   , typename = typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    6269. 

  6269.         <a class="reference internal" href="#are-tagged-arguments"><tt class="docutils literal">are_tagged_arguments</tt></a>&lt;TaggedArg0,TaggedArgs...&gt;
    6270. 

  6270.     &gt;::type
    6271. 

  6271. &gt;
    6272. 

  6272. inline explicit <strong>cls</strong>(
    6273. 

  6273.     TaggedArg0 const&amp; arg0
    6274. 

  6274.   , TaggedArgs const&amp;... args
    6275. 

  6275. ) : <strong>impl</strong>(<a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a>(arg0, args...))
    6276. 

  6276. {
    6277. 

  6277. }
    6278. 

  6278. </pre>
    6279. 

  6279. </div>
    6280. 

  6280. <div class="section" id="boost-parameter-no-spec-no-base-constructor-cls-impl">
    6281. 

  6281. <span id="boost-parameter-no-spec-no-base-constructor"></span><h2><a class="toc-backref" href="#id74">7.18&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR(cls, impl)</tt></a></h2>
    6282. 

  6282. <table class="docutils field-list" frame="void" rules="none">
    6283. 

  6283. <col class="field-name" />
    6284. 

  6284. <col class="field-body" />
    6285. 

  6285. <tbody valign="top">
    6286. 

  6286. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/preprocessor_no_spec.hpp">boost/parameter/preprocessor_no_spec.hpp</a></td>
    6287. 

  6287. </tr>
    6288. 

  6288. </tbody>
    6289. 

  6289. </table>
    6290. 

  6290. <p>Generates a constructor that can take in named arguments.</p>
    6291. 

  6291. <table class="docutils field-list" frame="void" rules="none">
    6292. 

  6292. <col class="field-name" />
    6293. 

  6293. <col class="field-body" />
    6294. 

  6294. <tbody valign="top">
    6295. 

  6295. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    6296. 

  6296. </tr>
    6297. 

  6297. </tbody>
    6298. 

  6298. </table>
    6299. 

  6299. <p>The return type of each of the following function templates falls under a
    6300. 

  6300. different value category.</p>
    6301. 

  6301. <pre class="literal-block">
    6302. 

  6302. template &lt;std::size_t N&gt;
    6303. 

  6303. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; rvalue_bitset()
    6304. 

  6304. {
    6305. 

  6305.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    6306. 

  6306. }
    6307. 

  6307. 

  6308. template &lt;std::size_t N&gt;
    6309. 

  6309. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const rvalue_const_bitset()
    6310. 

  6310. {
    6311. 

  6311.     return <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    6312. 

  6312. }
    6313. 

  6313. 

  6314. template &lt;std::size_t N&gt;
    6315. 

  6315. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp; lvalue_bitset()
    6316. 

  6316. {
    6317. 

  6317.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; lset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    6318. 

  6318.     return lset;
    6319. 

  6319. }
    6320. 

  6320. 

  6321. template &lt;std::size_t N&gt;
    6322. 

  6322. <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp; lvalue_const_bitset()
    6323. 

  6323. {
    6324. 

  6324.     static <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const clset = <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;();
    6325. 

  6325.     return clset;
    6326. 

  6326. }
    6327. 

  6327. </pre>
    6328. 

  6328. <p>The <tt class="docutils literal"><span class="pre">U::evaluate_category</span></tt> static member function template has a simple job:
    6329. 

  6329. to return the correct value category when passed in an object returned by one
    6330. 

  6330. of the functions defined above.  Assume that
    6331. 

  6331. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined.</p>
    6332. 

  6332. <pre class="literal-block">
    6333. 

  6333. enum invoked
    6334. 

  6334. {
    6335. 

  6335.     passed_by_lvalue_reference_to_const
    6336. 

  6336.   , passed_by_lvalue_reference
    6337. 

  6337.   , passed_by_rvalue_reference_to_const
    6338. 

  6338.   , passed_by_rvalue_reference
    6339. 

  6339. };
    6340. 

  6340. 

  6341. struct U
    6342. 

  6342. {
    6343. 

  6343.     template &lt;std::size_t N&gt;
    6344. 

  6344.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;)
    6345. 

  6345.     {
    6346. 

  6346.         return passed_by_lvalue_reference_to_const;
    6347. 

  6347.     }
    6348. 

  6348. 

  6349.     template &lt;std::size_t N&gt;
    6350. 

  6350.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;)
    6351. 

  6351.     {
    6352. 

  6352.         return passed_by_lvalue_reference;
    6353. 

  6353.     }
    6354. 

  6354. 

  6355.     template &lt;std::size_t N&gt;
    6356. 

  6356.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt; const&amp;&amp;)
    6357. 

  6357.     {
    6358. 

  6358.         return passed_by_rvalue_reference_to_const;
    6359. 

  6359.     }
    6360. 

  6360. 

  6361.     template &lt;std::size_t N&gt;
    6362. 

  6362.     static invoked evaluate_category(<a class="reference external" href="http://en.cppreference.com/w/cpp/utility/bitset">std::bitset</a>&lt;N + 1&gt;&amp;&amp;)
    6363. 

  6363.     {
    6364. 

  6364.         return passed_by_rvalue_reference;
    6365. 

  6365.     }
    6366. 

  6366. };
    6367. 

  6367. </pre>
    6368. 

  6368. <p>Named parameters are required when invoking the constructor; however, none of
    6369. 

  6369. their tags need to be in the same namespace.</p>
    6370. 

  6370. <pre class="literal-block">
    6371. 

  6371. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lrc, kw0) in(lrc))
    6372. 

  6372. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_lr, kw1) in_out(lr))
    6373. 

  6373. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rrc, kw2) in(rrc))
    6374. 

  6374. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>((_rr, kw3) consume(rr))
    6375. 

  6375. </pre>
    6376. 

  6376. <p>Unlike <a class="reference internal" href="#boost-parameter-no-spec-constructor"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR</tt></a>, this macro doesn't require a
    6377. 

  6377. base class, only a delegate function to which the generated constructor can
    6378. 

  6378. pass its <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a>.</p>
    6379. 

  6379. <pre class="literal-block">
    6380. 

  6380. struct D
    6381. 

  6381. {
    6382. 

  6382.     BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR(D, D::_evaluate)
    6383. 

  6383. 

  6384.  private:
    6385. 

  6385.     template &lt;typename Args&gt;
    6386. 

  6386.     static bool _evaluate(Args const&amp; args)
    6387. 

  6387.     {
    6388. 

  6388.         BOOST_TEST_EQ(
    6389. 

  6389.             passed_by_lvalue_reference_to_const
    6390. 

  6390.           , U::evaluate_category&lt;0&gt;(args[_lrc])
    6391. 

  6391.         );
    6392. 

  6392.         BOOST_TEST_EQ(
    6393. 

  6393.             passed_by_lvalue_reference
    6394. 

  6394.           , U::evaluate_category&lt;1&gt;(args[_lr])
    6395. 

  6395.         );
    6396. 

  6396.         BOOST_TEST_EQ(
    6397. 

  6397.             passed_by_rvalue_reference_to_const
    6398. 

  6398.           , U::evaluate_category&lt;2&gt;(
    6399. 

  6399.                 args[_rrc | rvalue_const_bitset&lt;2&gt;()]
    6400. 

  6400.             )
    6401. 

  6401.         );
    6402. 

  6402.         BOOST_TEST_EQ(
    6403. 

  6403.             passed_by_rvalue_reference
    6404. 

  6404.           , U::evaluate_category&lt;3&gt;(
    6405. 

  6405.                 args[_rr | rvalue_bitset&lt;3&gt;()]
    6406. 

  6406.             )
    6407. 

  6407.         );
    6408. 

  6408. 

  6409.         return true;
    6410. 

  6410.     }
    6411. 

  6411. };
    6412. 

  6412. </pre>
    6413. 

  6413. <p>To invoke the constructor, bind all its arguments to named parameters.</p>
    6414. 

  6414. <pre class="literal-block">
    6415. 

  6415. D dp0(
    6416. 

  6416.     _rr0 = rvalue_bitset&lt;3&gt;()
    6417. 

  6417.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    6418. 

  6418.   , _lr0 = lvalue_bitset&lt;1&gt;()
    6419. 

  6419.   , _rrc0 = rvalue_const_bitset&lt;2&gt;()
    6420. 

  6420. );
    6421. 

  6421. D dp1(
    6422. 

  6422.     _lr0 = lvalue_bitset&lt;1&gt;()
    6423. 

  6423.   , _lrc0 = lvalue_const_bitset&lt;0&gt;()
    6424. 

  6424. );
    6425. 

  6425. </pre>
    6426. 

  6426. <p>The <a class="reference external" href="../../test/preprocessor_eval_cat_no_spec.cpp">preprocessor_eval_cat_no_spec.cpp</a> test program demonstrates proper usage of
    6427. 

  6427. this macro.</p>
    6428. 

  6428. <p><strong>Macro parameters:</strong></p>
    6429. 

  6429. <ul class="simple">
    6430. 

  6430. <li><tt class="docutils literal">cls</tt> is the name of the enclosing class.</li>
    6431. 

  6431. <li><tt class="docutils literal">func</tt> is a function that takes in the <a class="reference internal" href="#argumentpack"><span class="concept">ArgumentPack</span></a> that the
    6432. 

  6432. generated constructor passes on.</li>
    6433. 

  6433. </ul>
    6434. 

  6434. <p><strong>Argument specifiers syntax:</strong></p>
    6435. 

  6435. <p>None.</p>
    6436. 

  6436. <p><strong>Approximate expansion:</strong></p>
    6437. 

  6437. <pre class="literal-block">
    6438. 

  6438. template &lt;
    6439. 

  6439.     typename TaggedArg0
    6440. 

  6440.   , typename ...TaggedArgs
    6441. 

  6441.   , typename = typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;
    6442. 

  6442.         <a class="reference internal" href="#are-tagged-arguments"><tt class="docutils literal">are_tagged_arguments</tt></a>&lt;TaggedArg0,TaggedArgs...&gt;
    6443. 

  6443.     &gt;::type
    6444. 

  6444. &gt;
    6445. 

  6445. inline explicit <strong>cls</strong>(
    6446. 

  6446.     TaggedArg0 const&amp; arg0
    6447. 

  6447.   , TaggedArgs const&amp;... args
    6448. 

  6448. )
    6449. 

  6449. {
    6450. 

  6450.     <strong>func</strong>(<a class="reference internal" href="#compose"><tt class="docutils literal">compose</tt></a>(arg0, args...));
    6451. 

  6451. }
    6452. 

  6452. </pre>
    6453. 

  6453. </div>
    6454. 

  6454. <div class="section" id="boost-parameter-name-name">
    6455. 

  6455. <span id="boost-parameter-name"></span><h2><a class="toc-backref" href="#id75">7.19&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NAME(name)</tt></a></h2>
    6456. 

  6456. <table class="docutils field-list" frame="void" rules="none">
    6457. 

  6457. <col class="field-name" />
    6458. 

  6458. <col class="field-body" />
    6459. 

  6459. <tbody valign="top">
    6460. 

  6460. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/name.hpp">boost/parameter/name.hpp</a></td>
    6461. 

  6461. </tr>
    6462. 

  6462. </tbody>
    6463. 

  6463. </table>
    6464. 

  6464. <p>Declares a tag-type and keyword object.</p>
    6465. 

  6465. <p><strong>If</strong> <em>name</em> is of the form:</p>
    6466. 

  6466. <pre class="literal-block">
    6467. 

  6467. (<em>object-name</em>, <em>namespace-name</em>) <em>qualifier</em>(<em>tag-name</em>)
    6468. 

  6468. </pre>
    6469. 

  6469. <p><strong>then</strong></p>
    6470. 

  6470. <table class="docutils field-list" frame="void" rules="none">
    6471. 

  6471. <col class="field-name" />
    6472. 

  6472. <col class="field-body" />
    6473. 

  6473. <tbody valign="top">
    6474. 

  6474. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><em>qualifier</em> is either <tt class="docutils literal">in</tt>, <tt class="docutils literal">out</tt>, <tt class="docutils literal">in_out</tt>, <tt class="docutils literal">consume</tt>,
    6475. 

  6475. <tt class="docutils literal">move_from</tt>, or <tt class="docutils literal">forward</tt>.</td>
    6476. 

  6476. </tr>
    6477. 

  6477. <tr class="field"><th class="field-name">Expands to:</th><td class="field-body"></td>
    6478. 

  6478. </tr>
    6479. 

  6479. </tbody>
    6480. 

  6480. </table>
    6481. 

  6481. <pre class="literal-block">
    6482. 

  6482. namespace <em>namespace-name</em> {
    6483. 

  6483. 

  6484.     struct <em>tag-name</em>
    6485. 

  6485.     {
    6486. 

  6486.         static constexpr char const* keyword_name()
    6487. 

  6487.         {
    6488. 

  6488.             return ## <em>tag-name</em>;
    6489. 

  6489.         }
    6490. 

  6490. 

  6491.         typedef <em>unspecified</em> _;
    6492. 

  6492.         typedef <em>unspecified</em> _1;
    6493. 

  6493.         typedef boost::parameter::<em>qualifier</em> ## _reference qualifier;
    6494. 

  6494. 

  6495.         // The following definitions are available only when
    6496. 

  6496.         // <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> is defined.
    6497. 

  6497. 

  6498.         template &lt;typename ArgumentPack&gt;
    6499. 

  6499.         using binding_fn = typename <a class="reference internal" href="#binding"><tt class="docutils literal">binding</tt></a>&lt;
    6500. 

  6500.             ArgumentPack
    6501. 

  6501.           , <em>tag-name</em>
    6502. 

  6502.         &gt;::type;
    6503. 

  6503. 

  6504.         template &lt;typename ArgumentPack&gt;
    6505. 

  6505.         using fn = typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;ArgumentPack, <em>tag-name</em>&gt;::type;
    6506. 

  6506.     };
    6507. 

  6507. }
    6508. 

  6508. 

  6509. <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;<em>tag-namespace</em>::<em>tag-name</em>&gt; const&amp; <em>object-name</em>
    6510. 

  6510.     = <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;<em>tag-namespace</em>::<em>tag-name</em>&gt;::instance;
    6511. 

  6511. </pre>
    6512. 

  6512. <p><strong>Else If</strong> <em>name</em> is of the form:</p>
    6513. 

  6513. <pre class="literal-block">
    6514. 

  6514. (<em>tag-name</em>, <em>namespace-name</em>) <em>object-name</em>
    6515. 

  6515. </pre>
    6516. 

  6516. <p><strong>then</strong></p>
    6517. 

  6517. <p>Treats <em>name</em> as if it were of the form:</p>
    6518. 

  6518. <pre class="literal-block">
    6519. 

  6519. (forward(<em>tag-name</em>), <em>namespace-name</em>) <em>object-name</em>
    6520. 

  6520. </pre>
    6521. 

  6521. <p><strong>Else If</strong> <em>name</em> is of the form:</p>
    6522. 

  6522. <pre class="literal-block">
    6523. 

  6523. <em>qualifier</em>(<em>tag-name</em>)
    6524. 

  6524. </pre>
    6525. 

  6525. <p><strong>then</strong></p>
    6526. 

  6526. <table class="docutils field-list" frame="void" rules="none">
    6527. 

  6527. <col class="field-name" />
    6528. 

  6528. <col class="field-body" />
    6529. 

  6529. <tbody valign="top">
    6530. 

  6530. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><em>qualifier</em> is either <tt class="docutils literal">in</tt>, <tt class="docutils literal">out</tt>, <tt class="docutils literal">in_out</tt>, <tt class="docutils literal">consume</tt>,
    6531. 

  6531. <tt class="docutils literal">move_from</tt>, or <tt class="docutils literal">forward</tt>.</td>
    6532. 

  6532. </tr>
    6533. 

  6533. <tr class="field"><th class="field-name">Expands to:</th><td class="field-body"></td>
    6534. 

  6534. </tr>
    6535. 

  6535. </tbody>
    6536. 

  6536. </table>
    6537. 

  6537. <pre class="literal-block">
    6538. 

  6538. namespace tag {
    6539. 

  6539. 

  6540.     struct <em>tag-name</em>
    6541. 

  6541.     {
    6542. 

  6542.         static constexpr char const* keyword_name()
    6543. 

  6543.         {
    6544. 

  6544.             return ## <em>tag-name</em>;
    6545. 

  6545.         }
    6546. 

  6546. 

  6547.         typedef <em>unspecified</em> _;
    6548. 

  6548.         typedef <em>unspecified</em> _1;
    6549. 

  6549.         typedef boost::parameter::<em>qualifier</em> ## _reference qualifier;
    6550. 

  6550. 

  6551.         // The following definitions are available only when
    6552. 

  6552.         // <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> is defined.
    6553. 

  6553. 

  6554.         template &lt;typename ArgumentPack&gt;
    6555. 

  6555.         using binding_fn = typename <a class="reference internal" href="#binding"><tt class="docutils literal">binding</tt></a>&lt;
    6556. 

  6556.             ArgumentPack
    6557. 

  6557.           , <em>tag-name</em>
    6558. 

  6558.         &gt;::type;
    6559. 

  6559. 

  6560.         template &lt;typename ArgumentPack&gt;
    6561. 

  6561.         using fn = typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;ArgumentPack, <em>tag-name</em>&gt;::type;
    6562. 

  6562.     };
    6563. 

  6563. }
    6564. 

  6564. 

  6565. <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;tag::<em>tag-name</em>&gt; const&amp; _ ## <em>tag-name</em>
    6566. 

  6566.     = <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;tag::<em>tag-name</em>&gt;::instance;
    6567. 

  6567. </pre>
    6568. 

  6568. <p><strong>Else</strong></p>
    6569. 

  6569. <p>Treats <em>name</em> as if it were of the form:</p>
    6570. 

  6570. <pre class="literal-block">
    6571. 

  6571. forward(<em>tag-name</em>)
    6572. 

  6572. </pre>
    6573. 

  6573. </div>
    6574. 

  6574. <div class="section" id="boost-parameter-nested-keyword-tag-namespace-name-alias">
    6575. 

  6575. <span id="boost-parameter-nested-keyword"></span><h2><a class="toc-backref" href="#id76">7.20&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_NESTED_KEYWORD(tag_namespace, name, alias)</tt></a></h2>
    6576. 

  6576. <table class="docutils field-list" frame="void" rules="none">
    6577. 

  6577. <col class="field-name" />
    6578. 

  6578. <col class="field-body" />
    6579. 

  6579. <tbody valign="top">
    6580. 

  6580. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/nested_keyword.hpp">boost/parameter/nested_keyword.hpp</a></td>
    6581. 

  6581. </tr>
    6582. 

  6582. </tbody>
    6583. 

  6583. </table>
    6584. 

  6584. <p>Declares a tag-type, a keyword object, and an alias for that object nested in
    6585. 

  6585. the tag-type.</p>
    6586. 

  6586. <p><strong>If</strong> <em>name</em> is of the form:</p>
    6587. 

  6587. <pre class="literal-block">
    6588. 

  6588. <em>qualifier</em>(<em>tag-name</em>)
    6589. 

  6589. </pre>
    6590. 

  6590. <p><strong>then</strong></p>
    6591. 

  6591. <table class="docutils field-list" frame="void" rules="none">
    6592. 

  6592. <col class="field-name" />
    6593. 

  6593. <col class="field-body" />
    6594. 

  6594. <tbody valign="top">
    6595. 

  6595. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><em>qualifier</em> is either <tt class="docutils literal">in</tt>, <tt class="docutils literal">out</tt>, <tt class="docutils literal">in_out</tt>, <tt class="docutils literal">consume</tt>,
    6596. 

  6596. <tt class="docutils literal">move_from</tt>, or <tt class="docutils literal">forward</tt>.</td>
    6597. 

  6597. </tr>
    6598. 

  6598. <tr class="field"><th class="field-name">Expands to:</th><td class="field-body"></td>
    6599. 

  6599. </tr>
    6600. 

  6600. </tbody>
    6601. 

  6601. </table>
    6602. 

  6602. <pre class="literal-block">
    6603. 

  6603. namespace tag {
    6604. 

  6604. 

  6605.     struct <em>tag-name</em>
    6606. 

  6606.     {
    6607. 

  6607.         static constexpr char const* keyword_name()
    6608. 

  6608.         {
    6609. 

  6609.             return ## <em>tag-name</em> ## _;
    6610. 

  6610.         }
    6611. 

  6611. 

  6612.         typedef <em>unspecified</em> _;
    6613. 

  6613.         typedef <em>unspecified</em> _1;
    6614. 

  6614.         typedef boost::parameter::<em>qualifier</em> ## _reference qualifier;
    6615. 

  6615.         static <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;<em>tag-name</em>&gt; const&amp; <em>alias</em>;
    6616. 

  6616. 

  6617.         // The following definitions are available only when
    6618. 

  6618.         // <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> is defined.
    6619. 

  6619. 

  6620.         template &lt;typename ArgumentPack&gt;
    6621. 

  6621.         using binding_fn = typename <a class="reference internal" href="#binding"><tt class="docutils literal">binding</tt></a>&lt;
    6622. 

  6622.             ArgumentPack
    6623. 

  6623.           , <em>tag-name</em>
    6624. 

  6624.         &gt;::type;
    6625. 

  6625. 

  6626.         template &lt;typename ArgumentPack&gt;
    6627. 

  6627.         using fn = typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;ArgumentPack, <em>tag-name</em>&gt;::type;
    6628. 

  6628.     };
    6629. 

  6629. 

  6630.     <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;<em>tag-name</em>&gt; const&amp; tag::<em>tag-name</em>::<em>alias</em>
    6631. 

  6631.         = <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;<em>tag-name</em>&gt;::instance;
    6632. 

  6632. }
    6633. 

  6633. 

  6634. <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;tag::<em>tag-name</em>&gt; const&amp; tag::<em>tag-name</em>::<em>name</em>
    6635. 

  6635.     = <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;tag::<em>tag-name</em>&gt;::instance;
    6636. 

  6636. </pre>
    6637. 

  6637. <p><strong>Else</strong></p>
    6638. 

  6638. <p>Treats <em>name</em> as if it were of the form:</p>
    6639. 

  6639. <pre class="literal-block">
    6640. 

  6640. forward(<em>tag-name</em>)
    6641. 

  6641. </pre>
    6642. 

  6642. </div>
    6643. 

  6643. <div class="section" id="boost-parameter-template-keyword-name">
    6644. 

  6644. <span id="boost-parameter-template-keyword"></span><h2><a class="toc-backref" href="#id77">7.21&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_TEMPLATE_KEYWORD(name)</tt></a></h2>
    6645. 

  6645. <table class="docutils field-list" frame="void" rules="none">
    6646. 

  6646. <col class="field-name" />
    6647. 

  6647. <col class="field-body" />
    6648. 

  6648. <tbody valign="top">
    6649. 

  6649. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/template_keyword.hpp">boost/parameter/template_keyword.hpp</a></td>
    6650. 

  6650. </tr>
    6651. 

  6651. <tr class="field"><th class="field-name">Included by:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/name.hpp">boost/parameter/name.hpp</a></td>
    6652. 

  6652. </tr>
    6653. 

  6653. <tr class="field"><th class="field-name">Expands to:</th><td class="field-body"></td>
    6654. 

  6654. </tr>
    6655. 

  6655. </tbody>
    6656. 

  6656. </table>
    6657. 

  6657. <pre class="literal-block">
    6658. 

  6658. namespace tag {
    6659. 

  6659. 

  6660.     struct <em>name</em>;
    6661. 

  6661. }
    6662. 

  6662. 

  6663. template &lt;typename T&gt;
    6664. 

  6664. struct <em>name</em> : <a class="reference internal" href="#template-keyword"><tt class="docutils literal">template_keyword</tt></a>&lt;tag:: <em>name</em>, T&gt;
    6665. 

  6665. {
    6666. 

  6666. };
    6667. 

  6667. </pre>
    6668. 

  6668. <p>The <a class="reference external" href="../../test/function_type_tpl_param.cpp">function_type_tpl_param.cpp</a> test program demonstrates proper usage of
    6669. 

  6669. this macro.</p>
    6670. 

  6670. </div>
    6671. 

  6671. <div class="section" id="boost-parameter-fun-r-n-l-h-p">
    6672. 

  6672. <span id="boost-parameter-fun"></span><h2><a class="toc-backref" href="#id78">7.22&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_FUN(r, n, l, h, p)</tt></a></h2>
    6673. 

  6673. <div class="admonition-deprecated admonition">
    6674. 

  6674. <p class="first admonition-title">Deprecated</p>
    6675. 

  6675. <p class="last">This macro has been deprecated in favor of
    6676. 

  6676. <tt class="docutils literal">BOOST_PARAMETER_FUNCTION</tt>.</p>
    6677. 

  6677. </div>
    6678. 

  6678. <p>Generates a sequence of <a class="reference external" href="index.html#forwarding-functions">forwarding function</a> templates named
    6679. 

  6679. <tt class="docutils literal">n</tt>, with arities ranging from <tt class="docutils literal">l</tt> to <tt class="docutils literal">h</tt>, returning <tt class="docutils literal">r</tt>,
    6680. 

  6680. and using <tt class="docutils literal">p</tt> to control overload resolution and assign tags to
    6681. 

  6681. positional arguments.</p>
    6682. 

  6682. <table class="docutils field-list" frame="void" rules="none">
    6683. 

  6683. <col class="field-name" />
    6684. 

  6684. <col class="field-body" />
    6685. 

  6685. <tbody valign="top">
    6686. 

  6686. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/macros.hpp">boost/parameter/macros.hpp</a></td>
    6687. 

  6687. </tr>
    6688. 

  6688. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal">l</tt> and <tt class="docutils literal">h</tt> are nonnegative integer tokens
    6689. 

  6689. such that <tt class="docutils literal">l</tt> &lt; <tt class="docutils literal">h</tt></td>
    6690. 

  6690. </tr>
    6691. 

  6691. <tr class="field"><th class="field-name">Expands to:</th><td class="field-body"></td>
    6692. 

  6692. </tr>
    6693. 

  6693. </tbody>
    6694. 

  6694. </table>
    6695. 

  6695. <pre class="literal-block">
    6696. 

  6696. template &lt;typename A1, typename A2, …, typename A ## <strong>l</strong>&gt;
    6697. 

  6697. r
    6698. 

  6698.     name(
    6699. 

  6699.         A1 &amp;&amp; a1, A2 &amp;&amp; a2, …, A ## <strong>l</strong> &amp;&amp; a ## <strong>l</strong>
    6700. 

  6700.       , typename <strong>p</strong>::match&lt;A1, A2, …, A ## <strong>l</strong>&gt;::type p = <strong>p</strong>()
    6701. 

  6701.     )
    6702. 

  6702. {
    6703. 

  6703.     return <strong>name</strong>_with_named_params(
    6704. 

  6704.         <strong>p</strong>(
    6705. 

  6705.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A1&gt;(a1)
    6706. 

  6706.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A2&gt;(a2)
    6707. 

  6707.           , …
    6708. 

  6708.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>l</strong>&gt;(a ## <strong>l</strong>)
    6709. 

  6709.         )
    6710. 

  6710.     );
    6711. 

  6711. }
    6712. 

  6712. 

  6713. template &lt;
    6714. 

  6714.     typename A1
    6715. 

  6715.   , typename A2
    6716. 

  6716.   , …
    6717. 

  6717.   , typename A ## <strong>l</strong>
    6718. 

  6718.   , typename A ## <a class="reference external" href="../../../preprocessor/doc/ref/inc.html">BOOST_PP_INC</a>(<strong>l</strong>)
    6719. 

  6719. &gt;
    6720. 

  6720. r
    6721. 

  6721.     name(
    6722. 

  6722.         A1 &amp;&amp; a1, A2 &amp;&amp; a2, …, A ## <strong>l</strong> &amp;&amp; a ## <strong>l</strong>
    6723. 

  6723.       , A ## <a class="reference external" href="../../../preprocessor/doc/ref/inc.html">BOOST_PP_INC</a>(<strong>l</strong>) const&amp; a ## <a class="reference external" href="../../../preprocessor/doc/ref/inc.html">BOOST_PP_INC</a>(<strong>l</strong>)
    6724. 

  6724.       , typename <strong>p</strong>::match&lt;
    6725. 

  6725.             A1, A2, …, A ## <strong>l</strong>, A ## <a class="reference external" href="../../../preprocessor/doc/ref/inc.html">BOOST_PP_INC</a>(<strong>l</strong>)
    6726. 

  6726.         &gt;::type p = <strong>p</strong>()
    6727. 

  6727.     )
    6728. 

  6728. {
    6729. 

  6729.     return <strong>name</strong>_with_named_params(
    6730. 

  6730.         <strong>p</strong>(
    6731. 

  6731.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A1&gt;(a1)
    6732. 

  6732.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A2&gt;(a2)
    6733. 

  6733.           , …
    6734. 

  6734.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>l</strong>&gt;(a ## <strong>l</strong>)
    6735. 

  6735.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <a class="reference external" href="../../../preprocessor/doc/ref/inc.html">BOOST_PP_INC</a>(<strong>l</strong>)&gt;(
    6736. 

  6736.                 a ## <a class="reference external" href="../../../preprocessor/doc/ref/inc.html">BOOST_PP_INC</a>(<strong>l</strong>)
    6737. 

  6737.             )
    6738. 

  6738.         )
    6739. 

  6739.     );
    6740. 

  6740. }
    6741. 

  6741. 

  6742. <span class="vellipsis">⋮</span>
    6743. 

  6743. 

  6744. template &lt;typename A1, typename A2, …, typename A ## <strong>h</strong>&gt;
    6745. 

  6745. r
    6746. 

  6746.     name(
    6747. 

  6747.         A1 &amp;&amp; a1, A2 &amp;&amp; a2, …, A ## <strong>h</strong> &amp;&amp; x ## <strong>h</strong>
    6748. 

  6748.       , typename <strong>p</strong>::match&lt;A1, A2, …, A ## <strong>h</strong>&gt;::type p = <strong>p</strong>()
    6749. 

  6749.     )
    6750. 

  6750. {
    6751. 

  6751.     return <strong>name</strong>_with_named_params(
    6752. 

  6752.         <strong>p</strong>(
    6753. 

  6753.             <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A1&gt;(a1)
    6754. 

  6754.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A2&gt;(a2)
    6755. 

  6755.           , …
    6756. 

  6756.           , <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/forward">std::forward</a>&lt;A ## <strong>h</strong>&gt;(a ## <strong>h</strong>)
    6757. 

  6757.         )
    6758. 

  6758.     );
    6759. 

  6759. }
    6760. 

  6760. </pre>
    6761. 

  6761. <p>The <a class="reference external" href="../../test/macros.cpp">macros.cpp</a> and <a class="reference external" href="../../test/macros_eval_category.cpp">macros_eval_category.cpp</a> test programs demonstrate proper
    6762. 

  6762. usage of this macro.</p>
    6763. 

  6763. </div>
    6764. 

  6764. <div class="section" id="boost-parameter-keyword-n-k">
    6765. 

  6765. <span id="boost-parameter-keyword"></span><h2><a class="toc-backref" href="#id79">7.23&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_KEYWORD(n, k)</tt></a></h2>
    6766. 

  6766. <div class="admonition-deprecated admonition">
    6767. 

  6767. <p class="first admonition-title">Deprecated</p>
    6768. 

  6768. <p class="last">This macro has been deprecated in favor of
    6769. 

  6769. <tt class="docutils literal">BOOST_PARAMETER_NAME</tt>.</p>
    6770. 

  6770. </div>
    6771. 

  6771. <p>Generates the declaration of a <a class="reference internal" href="#keyword-tag-type">keyword tag type</a> named <tt class="docutils literal">k</tt> in
    6772. 

  6772. namespace <tt class="docutils literal">n</tt> and a corresponding <a class="reference internal" href="#keyword-object">keyword object</a> definition in
    6773. 

  6773. the enclosing namespace.</p>
    6774. 

  6774. <table class="docutils field-list" frame="void" rules="none">
    6775. 

  6775. <col class="field-name" />
    6776. 

  6776. <col class="field-body" />
    6777. 

  6777. <tbody valign="top">
    6778. 

  6778. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/keyword.hpp">boost/parameter/keyword.hpp</a></td>
    6779. 

  6779. </tr>
    6780. 

  6780. <tr class="field"><th class="field-name">Expands to:</th><td class="field-body"></td>
    6781. 

  6781. </tr>
    6782. 

  6782. </tbody>
    6783. 

  6783. </table>
    6784. 

  6784. <pre class="literal-block">
    6785. 

  6785. namespace <strong>n</strong> {
    6786. 

  6786. 

  6787.     struct <strong>k</strong>
    6788. 

  6788.     {
    6789. 

  6789.         static constexpr char const* keyword_name()
    6790. 

  6790.         {
    6791. 

  6791.             return ## <em>k</em>;
    6792. 

  6792.         }
    6793. 

  6793. 

  6794.         typedef <em>unspecified</em> _;
    6795. 

  6795.         typedef <em>unspecified</em> _1;
    6796. 

  6796.         typedef boost::parameter::forward_reference qualifier;
    6797. 

  6797. 

  6798.         // The following definitions are available only when
    6799. 

  6799.         // <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> is defined.
    6800. 

  6800. 

  6801.         template &lt;typename ArgumentPack&gt;
    6802. 

  6802.         using binding_fn = typename <a class="reference internal" href="#binding"><tt class="docutils literal">binding</tt></a>&lt;
    6803. 

  6803.             ArgumentPack
    6804. 

  6804.           , <em>k</em>
    6805. 

  6805.         &gt;::type;
    6806. 

  6806. 

  6807.         template &lt;typename ArgumentPack&gt;
    6808. 

  6808.         using fn = typename <a class="reference internal" href="#value-type"><tt class="docutils literal">value_type</tt></a>&lt;ArgumentPack, <em>k</em>&gt;::type;
    6809. 

  6809.     };
    6810. 

  6810. }
    6811. 

  6811. 

  6812. namespace {
    6813. 

  6813. 

  6814.     <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;<em>n</em>::<strong>k</strong>&gt; const&amp; <strong>k</strong>
    6815. 

  6815.         = <a class="reference internal" href="#keyword"><tt class="docutils literal">keyword</tt></a>&lt;<em>n</em>::<strong>k</strong>&gt;::instance;
    6816. 

  6816. }
    6817. 

  6817. </pre>
    6818. 

  6818. </div>
    6819. 

  6819. <div class="section" id="boost-parameter-match-p-a-x">
    6820. 

  6820. <h2><a class="toc-backref" href="#id80">7.24&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_MATCH(p, a, x)</tt></a></h2>
    6821. 

  6821. <p>Generates a defaulted parameter declaration for a <a class="reference external" href="index.html#forwarding-functions">forwarding function</a>.</p>
    6822. 

  6822. <table class="docutils field-list" frame="void" rules="none">
    6823. 

  6823. <col class="field-name" />
    6824. 

  6824. <col class="field-body" />
    6825. 

  6825. <tbody valign="top">
    6826. 

  6826. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/match.hpp">boost/parameter/match.hpp</a></td>
    6827. 

  6827. </tr>
    6828. 

  6828. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal">a</tt> is a <a class="reference external" href="../../../preprocessor/doc/data.html">Boost.Preprocessor sequence</a> of the form</td>
    6829. 

  6829. </tr>
    6830. 

  6830. </tbody>
    6831. 

  6831. </table>
    6832. 

  6832. <pre class="literal-block">
    6833. 

  6833. (A0)(A1)…(A ## <em>n</em>)
    6834. 

  6834. </pre>
    6835. 

  6835. <table class="docutils field-list" frame="void" rules="none">
    6836. 

  6836. <col class="field-name" />
    6837. 

  6837. <col class="field-body" />
    6838. 

  6838. <tbody valign="top">
    6839. 

  6839. <tr class="field"><th class="field-name">Expands to:</th><td class="field-body"></td>
    6840. 

  6840. </tr>
    6841. 

  6841. </tbody>
    6842. 

  6842. </table>
    6843. 

  6843. <pre class="literal-block">
    6844. 

  6844. typename <strong>p</strong>::match&lt;<strong>A0</strong>, <strong>A1</strong>, …, <strong>A</strong> ## <em>n</em>&gt;::type
    6845. 

  6845.     <strong>x</strong> = <strong>p</strong>()
    6846. 

  6846. </pre>
    6847. 

  6847. </div>
    6848. 

  6848. </div>
    6849. 

  6849. <div class="section" id="configuration-macros">
    6850. 

  6850. <h1><a class="toc-backref" href="#id81">8&nbsp;&nbsp;&nbsp;Configuration Macros</a></h1>
    6851. 

  6851. <div class="section" id="id21">
    6852. 

  6852. <span id="boost-parameter-has-perfect-forwarding"></span><h2><a class="toc-backref" href="#id82">8.1&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a></h2>
    6853. 

  6853. <p>Determines whether or not the library supports perfect forwarding, or the
    6854. 

  6854. preservation of parameter value categories.  Users can manually disable this
    6855. 

  6855. macro by <tt class="docutils literal">#defining</tt> the <a class="reference internal" href="#boost-parameter-disable-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING</tt></a>
    6856. 

  6856. macro.  Otherwise, the library will <tt class="docutils literal">#define</tt> this macro if and only if it
    6857. 

  6857. is not already defined, and if the configuration macros
    6858. 

  6858. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__03_defects"><tt class="docutils literal">BOOST_NO_FUNCTION_TEMPLATE_ORDERING</tt></a>, <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__03_defects"><tt class="docutils literal">BOOST_NO_SFINAE</tt></a>,
    6859. 

  6859. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_RVALUE_REFERENCES</tt></a>, <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_VARIADIC_TEMPLATES</tt></a>, and
    6860. 

  6860. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS</tt></a> are not already defined by
    6861. 

  6861. <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a>.</p>
    6862. 

  6862. <table class="docutils field-list" frame="void" rules="none">
    6863. 

  6863. <col class="field-name" />
    6864. 

  6864. <col class="field-body" />
    6865. 

  6865. <tbody valign="top">
    6866. 

  6866. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/config.hpp">boost/parameter/config.hpp</a></td>
    6867. 

  6867. </tr>
    6868. 

  6868. </tbody>
    6869. 

  6869. </table>
    6870. 

  6870. </div>
    6871. 

  6871. <div class="section" id="id22">
    6872. 

  6872. <span id="boost-parameter-disable-perfect-forwarding"></span><h2><a class="toc-backref" href="#id83">8.2&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING</tt></a></h2>
    6873. 

  6873. <p>It may be necessary to test user code in case perfect forwarding support is
    6874. 

  6874. unavailable.  Users can <tt class="docutils literal">#define</tt> this macro either in their project
    6875. 

  6875. settings or before including any library header files.  Doing so will leave
    6876. 

  6876. both <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> and
    6877. 

  6877. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> undefined.</p>
    6878. 

  6878. </div>
    6879. 

  6879. <div class="section" id="id23">
    6880. 

  6880. <span id="boost-parameter-can-use-mp11"></span><h2><a class="toc-backref" href="#id84">8.3&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a></h2>
    6881. 

  6881. <p>Determines whether or not the library can use <a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a>, a C++11
    6882. 

  6882. metaprogramming library.  Users can manually disable this macro by
    6883. 

  6883. <tt class="docutils literal">#defining</tt> the <a class="reference internal" href="#boost-parameter-disable-mp11-usage"><tt class="docutils literal">BOOST_PARAMETER_DISABLE_MP11_USAGE</tt></a> macro or the
    6884. 

  6884. <a class="reference internal" href="#boost-parameter-disable-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING</tt></a> macro.  Otherwise, the library
    6885. 

  6885. will <tt class="docutils literal">#define</tt> this macro if and only if it is not already defined, if
    6886. 

  6886. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is defined, and if the configuration
    6887. 

  6887. macros <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_CONSTEXPR</tt></a>, <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_DECLTYPE_N3276</tt></a>,
    6888. 

  6888. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_AUTO_DECLARATIONS</tt></a>, <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_TEMPLATE_ALIASES</tt></a>,
    6889. 

  6889. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_STATIC_ASSERT</tt></a>, <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_HDR_TYPE_TRAITS</tt></a>,
    6890. 

  6890. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_HDR_INITIALIZER_LIST</tt></a>, and <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_HDR_TUPLE</tt></a>
    6891. 

  6891. are not already defined by <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a>.</p>
    6892. 

  6892. <div class="admonition-usage-note admonition">
    6893. 

  6893. <p class="first admonition-title">Usage Note</p>
    6894. 

  6894. <p class="last"><a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a> and <a class="reference external" href="../../../mpl/doc/index.html">Boost.MPL</a> are <strong>not</strong> mutually exclusive.  It's
    6895. 

  6895. perfectly acceptable to specify deduced parameters using both quoted
    6896. 

  6896. metafunctions and metafunction classes, for example.  See
    6897. 

  6897. <a class="reference external" href="../../test/evaluate_category.cpp">evaluate_category.cpp</a>.</p>
    6898. 

  6898. </div>
    6899. 

  6899. <table class="docutils field-list" frame="void" rules="none">
    6900. 

  6900. <col class="field-name" />
    6901. 

  6901. <col class="field-body" />
    6902. 

  6902. <tbody valign="top">
    6903. 

  6903. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/config.hpp">boost/parameter/config.hpp</a></td>
    6904. 

  6904. </tr>
    6905. 

  6905. <tr class="field"><th class="field-name">Example usage:</th><td class="field-body"></td>
    6906. 

  6906. </tr>
    6907. 

  6907. </tbody>
    6908. 

  6908. </table>
    6909. 

  6909. <p>Given the following definitions:</p>
    6910. 

  6910. <pre class="literal-block">
    6911. 

  6911. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(x)
    6912. 

  6912. 

  6913. template &lt;typename A0&gt;
    6914. 

  6914. typename <a class="reference external" href="../../../core/doc/html/core/enable_if.html">boost::enable_if</a>&lt;<a class="reference external" href="http://en.cppreference.com/w/cpp/types/is_same">std::is_same</a>&lt;int,A0&gt;,int&gt;::type
    6915. 

  6915.     sfinae(A0 const&amp; a0)
    6916. 

  6916. {
    6917. 

  6917.     return 0;
    6918. 

  6918. }
    6919. 

  6919. </pre>
    6920. 

  6920. <p><a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a> allows deduced parameters to be defined more succinctly:</p>
    6921. 

  6921. <pre class="literal-block">
    6922. 

  6922. template &lt;typename T, typename Args&gt;
    6923. 

  6923. using predicate = <a class="reference external" href="http://en.cppreference.com/w/cpp/types/is_convertible">std::is_convertible</a>&lt;T,char const*&gt;;
    6924. 

  6924. 

  6925. <a class="reference internal" href="#boost-parameter-function"><tt class="docutils literal">BOOST_PARAMETER_FUNCTION</tt></a>((int), sfinae, tag,
    6926. 

  6926.     (deduced
    6927. 

  6927.         (optional
    6928. 

  6928.             (x
    6929. 

  6929.               , *(<a class="reference external" href="../../../mp11/doc/html/mp11.html#mp_quotef">boost::mp11::mp_quote</a>&lt;predicate&gt;)
    6930. 

  6930.               , static_cast&lt;char const*&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    6931. 

  6931.             )
    6932. 

  6932.         )
    6933. 

  6933.     )
    6934. 

  6934. )
    6935. 

  6935. {
    6936. 

  6936.     return 1;
    6937. 

  6937. }
    6938. 

  6938. </pre>
    6939. 

  6939. <p>Without <a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a>, deduced parameter definitions tend to be more verbose:</p>
    6940. 

  6940. <pre class="literal-block">
    6941. 

  6941. struct predicate
    6942. 

  6942. {
    6943. 

  6943.     template &lt;typename T, typename Args&gt;
    6944. 

  6944.     struct apply
    6945. 

  6945.       : <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    6946. 

  6946.             <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_convertible.html">boost::is_convertible</a>&lt;T,char const*&gt;
    6947. 

  6947.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a>  // Still have to convert to a
    6948. 

  6948.           , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean Integral Constant</a>.
    6949. 

  6949.         &gt;
    6950. 

  6950.     {
    6951. 

  6951.     };
    6952. 

  6952. };
    6953. 

  6953. 

  6954. <a class="reference internal" href="#boost-parameter-function"><tt class="docutils literal">BOOST_PARAMETER_FUNCTION</tt></a>((int), sfinae, tag,
    6955. 

  6955.     (deduced
    6956. 

  6956.         (optional
    6957. 

  6957.             (x
    6958. 

  6958.               , *(predicate)
    6959. 

  6959.               , static_cast&lt;char const*&gt;(<a class="reference external" href="http://en.cppreference.com/w/cpp/language/nullptr">std::nullptr</a>)
    6960. 

  6960.             )
    6961. 

  6961.         )
    6962. 

  6962.     )
    6963. 

  6963. )
    6964. 

  6964. {
    6965. 

  6965.     return 1;
    6966. 

  6966. }
    6967. 

  6967. </pre>
    6968. 

  6968. <p>Either way, the following assertions will succeed:</p>
    6969. 

  6969. <pre class="literal-block">
    6970. 

  6970. assert(1 == sfinae());
    6971. 

  6971. assert(1 == sfinae(&quot;foo&quot;));
    6972. 

  6972. assert(0 == sfinae(1));
    6973. 

  6973. </pre>
    6974. 

  6974. <p>As another example, given the following declarations and definitions:</p>
    6975. 

  6975. <pre class="literal-block">
    6976. 

  6976. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(x)
    6977. 

  6977. <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a>(y)
    6978. 

  6978. 

  6979. template &lt;typename E, typename Args&gt;
    6980. 

  6980. void check0(E const&amp; e, Args const&amp; args);
    6981. 

  6981. 

  6982. template &lt;typename P, typename E, typename ...Args&gt;
    6983. 

  6983. void check(E const&amp; e, Args const&amp;... args)
    6984. 

  6984. {
    6985. 

  6985.     check0(e, P()(args...));
    6986. 

  6986. }
    6987. 

  6987. </pre>
    6988. 

  6988. <p>Argument packs qualify as <a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a>-style lists containing
    6989. 

  6989. <a class="reference internal" href="#keyword-tag-type">keyword tag type</a>s:</p>
    6990. 

  6990. <pre class="literal-block">
    6991. 

  6991. template &lt;typename Args&gt;
    6992. 

  6992. struct some_functor
    6993. 

  6993. {
    6994. 

  6994.     template &lt;typename K&gt;
    6995. 

  6995.     void operator()(K&amp;&amp;) const
    6996. 

  6996.     {
    6997. 

  6997.         // K is one of tag::x, tag::y, etc.
    6998. 

  6998.     }
    6999. 

  6999. };
    7000. 

  7000. 

  7001. template &lt;typename E, typename Args&gt;
    7002. 

  7002. void check0(E const&amp; e, Args const&amp; args)
    7003. 

  7003. {
    7004. 

  7004.     boost::mp11::mp_for_each&lt;E&gt;(some_functor&lt;Args&gt;());
    7005. 

  7005. }
    7006. 

  7006. </pre>
    7007. 

  7007. <p>The first check determines whether or not the argument type of <tt class="docutils literal">_y</tt> is the
    7008. 

  7008. same as the reference type of <tt class="docutils literal">_x</tt>, while the second check determines
    7009. 

  7009. whether or not the argument type of <tt class="docutils literal">_y</tt> is convertible to the value type of
    7010. 

  7010. <tt class="docutils literal">_x</tt>.  Here, it's possible to access the reference and value result types of
    7011. 

  7011. indexing an argument pack a little more directly:</p>
    7012. 

  7012. <pre class="literal-block">
    7013. 

  7013. // Use mp_bind on tag::x::binding_fn to access the reference type of _x.
    7014. 

  7014. check&lt;
    7015. 

  7015.     <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    7016. 

  7016.         tag::x
    7017. 

  7017.       , <a class="reference internal" href="#optional"><tt class="docutils literal">optional</tt></a>&lt;
    7018. 

  7018.             <a class="reference internal" href="#deduced"><tt class="docutils literal">deduced</tt></a>&lt;tag::y&gt;
    7019. 

  7019.           , <a class="reference external" href="../../../mp11/doc/html/mp11.html#mp_bindf_t">boost::mp11::mp_bind</a>&lt;
    7020. 

  7020.                 <a class="reference external" href="http://en.cppreference.com/w/cpp/types/is_same">std::is_same</a> // <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>, standard version.
    7021. 

  7021.               , <a class="reference external" href="../../../mp11/doc/html/mp11.html#1_9">boost::mp11::_1</a> // will be bound to the argument type of _y.
    7022. 

  7022.               , <a class="reference external" href="../../../mp11/doc/html/mp11.html#mp_bindf_t">boost::mp11::mp_bind</a>&lt;
    7023. 

  7023.                     tag::x::binding_fn
    7024. 

  7024.                   , <a class="reference external" href="../../../mp11/doc/html/mp11.html#1_9">boost::mp11::_2</a> // will be bound to the argument pack type.
    7025. 

  7025.                 &gt;
    7026. 

  7026.             &gt;
    7027. 

  7027.         &gt;
    7028. 

  7028.     &gt;
    7029. 

  7029. &gt;((_x = 0, _y = 1), 0, 1);
    7030. 

  7030. 

  7031. // Use mp_bind_q on tag::x to access the value type of _x.
    7032. 

  7032. check&lt;
    7033. 

  7033.     <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    7034. 

  7034.         tag::x
    7035. 

  7035.       , <a class="reference internal" href="#optional"><tt class="docutils literal">optional</tt></a>&lt;
    7036. 

  7036.             <a class="reference internal" href="#deduced"><tt class="docutils literal">deduced</tt></a>&lt;tag::y&gt;
    7037. 

  7037.           , <a class="reference external" href="../../../mp11/doc/html/mp11.html#mp_bindf_t">boost::mp11::mp_bind</a>&lt;
    7038. 

  7038.                 <a class="reference external" href="http://en.cppreference.com/w/cpp/types/is_convertible">std::is_convertible</a> // <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_convertible.html">boost::is_convertible</a>, standard version.
    7039. 

  7039.               , <a class="reference external" href="../../../mp11/doc/html/mp11.html#1_9">boost::mp11::_1</a> // will be bound to the argument type of _y.
    7040. 

  7040.               , <a class="reference external" href="../../../mp11/doc/html/mp11.html#mp_bind_qq_t">boost::mp11::mp_bind_q</a>&lt;
    7041. 

  7041.                     tag::x
    7042. 

  7042.                   , <a class="reference external" href="../../../mp11/doc/html/mp11.html#1_9">boost::mp11::_2</a> // will be bound to the argument pack type.
    7043. 

  7043.                 &gt;
    7044. 

  7044.             &gt;
    7045. 

  7045.         &gt;
    7046. 

  7046.     &gt;
    7047. 

  7047. &gt;((_x = 0U, _y = 1U), 0U, 1U);
    7048. 

  7048. </pre>
    7049. 

  7049. <p>Argument packs still qualify as <a class="reference external" href="../../../mpl/doc/index.html">Boost.MPL</a>-style lists containing
    7050. 

  7050. <a class="reference internal" href="#keyword-tag-type">keyword tag type</a>s:</p>
    7051. 

  7051. <pre class="literal-block">
    7052. 

  7052. template &lt;typename Args&gt;
    7053. 

  7053. struct some_functor
    7054. 

  7054. {
    7055. 

  7055.     template &lt;typename K&gt;
    7056. 

  7056.     void operator()(K) const
    7057. 

  7057.     {
    7058. 

  7058.         // K is one of tag::x, tag::y, etc.
    7059. 

  7059.     }
    7060. 

  7060. };
    7061. 

  7061. 

  7062. template &lt;typename E, typename Args&gt;
    7063. 

  7063. void check0(E const&amp; e, Args const&amp; args)
    7064. 

  7064. {
    7065. 

  7065.     boost::mpl::for_each&lt;E&gt;(some_functor&lt;Args&gt;());
    7066. 

  7066. }
    7067. 

  7067. </pre>
    7068. 

  7068. <p>However, without <a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a>, the corresponding checks become a little more
    7069. 

  7069. verbose:</p>
    7070. 

  7070. <pre class="literal-block">
    7071. 

  7071. check&lt;
    7072. 

  7072.     <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    7073. 

  7073.         tag::x
    7074. 

  7074.       , <a class="reference internal" href="#optional"><tt class="docutils literal">optional</tt></a>&lt;
    7075. 

  7075.             <a class="reference internal" href="#deduced"><tt class="docutils literal">deduced</tt></a>&lt;tag::y&gt;
    7076. 

  7076.           , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    7077. 

  7077.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_same.html">boost::is_same</a>&lt;
    7078. 

  7078.                     <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/add_lvalue_reference.html">boost::add_lvalue_reference</a>&lt;<a class="reference external" href="../../../mp11/doc/html/mp11.html#1_9">boost::mp11::_1</a>&gt;
    7079. 

  7079.                   , <a class="reference internal" href="#binding"><tt class="docutils literal">binding</tt></a>&lt;<a class="reference external" href="../../../mp11/doc/html/mp11.html#1_9">boost::mp11::_2</a>, tag::x&gt;
    7080. 

  7080.                 &gt;
    7081. 

  7081.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a>  // Still have to convert to a
    7082. 

  7082.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean Integral Constant</a>.
    7083. 

  7083.             &gt;
    7084. 

  7084.         &gt;
    7085. 

  7085.     &gt;
    7086. 

  7086. &gt;((_x = 0, _y = 1), 0, 1);
    7087. 

  7087. 

  7088. // Use tag::x::_ or tag::x::_1 to access the value type of _x.
    7089. 

  7089. check&lt;
    7090. 

  7090.     <a class="reference internal" href="#parameters"><tt class="docutils literal">parameters</tt></a>&lt;
    7091. 

  7091.         tag::x
    7092. 

  7092.       , <a class="reference internal" href="#optional"><tt class="docutils literal">optional</tt></a>&lt;
    7093. 

  7093.             <a class="reference internal" href="#deduced"><tt class="docutils literal">deduced</tt></a>&lt;tag::y&gt;
    7094. 

  7094.           , <a class="reference external" href="../../../mpl/doc/refmanual/if.html">mpl::if_</a>&lt;
    7095. 

  7095.                 <a class="reference external" href="../../../type_traits/doc/html/boost_typetraits/is_convertible.html">boost::is_convertible</a>&lt;<a class="reference external" href="../../../mp11/doc/html/mp11.html#1_9">boost::mp11::_1</a>, tag::x::_1&gt;
    7096. 

  7096.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::true_</a>  // Still have to convert to a
    7097. 

  7097.               , <a class="reference external" href="../../../mpl/doc/refmanual/bool.html">mpl::false_</a> // <a class="reference external" href="../../../mpl/doc/refmanual/integral-constant.html">Boolean Integral Constant</a>.
    7098. 

  7098.             &gt;
    7099. 

  7099.         &gt;
    7100. 

  7100.     &gt;
    7101. 

  7101. &gt;((_x = 0U, _y = 1U), 0U, 1U);
    7102. 

  7102. </pre>
    7103. 

  7103. <p>The <a class="reference external" href="../../test/singular.cpp">singular.cpp</a>, <a class="reference external" href="../../test/compose.cpp">compose.cpp</a>, <a class="reference external" href="../../test/optional_deduced_sfinae.cpp">optional_deduced_sfinae.cpp</a>, and
    7104. 

  7104. <a class="reference external" href="../../test/deduced_dependent_predicate.cpp">deduced_dependent_predicate.cpp</a> test programs demonstrate proper usage of this
    7105. 

  7105. macro.</p>
    7106. 

  7106. </div>
    7107. 

  7107. <div class="section" id="id24">
    7108. 

  7108. <span id="boost-parameter-disable-mp11-usage"></span><h2><a class="toc-backref" href="#id85">8.4&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_DISABLE_MP11_USAGE</tt></a></h2>
    7109. 

  7109. <p>It may be necessary to disable usage of <a class="reference external" href="../../../mp11/doc/html/mp11.html">Boost.MP11</a> for compilers that
    7110. 

  7110. cannot support it.  Users can <tt class="docutils literal">#define</tt> this macro either in their project
    7111. 

  7111. settings or before including any library header files.  Doing so will leave
    7112. 

  7112. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> undefined.</p>
    7113. 

  7113. </div>
    7114. 

  7114. <div class="section" id="id25">
    7115. 

  7115. <span id="boost-parameter-variadic-mpl-sequence"></span><h2><a class="toc-backref" href="#id86">8.5&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE</tt></a></h2>
    7116. 

  7116. <p>If <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is <tt class="docutils literal">#defined</tt>, then determines
    7117. 

  7117. the <a class="reference external" href="../../../mpl/doc/refmanual/variadic-sequence.html">MPL Variadic Sequence</a> underlying the nested <tt class="docutils literal">parameter_spec</tt> type of
    7118. 

  7118. <tt class="docutils literal">parameters</tt>.  If the user does not manually <tt class="docutils literal">#define</tt> this macro, then the
    7119. 

  7119. library will <tt class="docutils literal">#define</tt> it as <a class="reference external" href="../../../mp11/doc/html/mp11.html#mp_listt"><tt class="docutils literal"><span class="pre">boost::mp11::mp_list</span></tt></a> if
    7120. 

  7120. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> is defined, <a class="reference external" href="../../../fusion/doc/html/fusion/container/list.html"><tt class="docutils literal"><span class="pre">boost::fusion::list</span></tt></a> if
    7121. 

  7121. <a class="reference external" href="../../../../boost/fusion/container/list/list_fwd.hpp"><tt class="docutils literal">BOOST_FUSION_HAS_VARIADIC_LIST</tt></a> is defined (by <a class="reference external" href="../../../fusion/doc/html/index.html">Boost.Fusion</a>),
    7122. 

  7122. <a class="reference external" href="../../../fusion/doc/html/fusion/container/deque.html"><tt class="docutils literal"><span class="pre">boost::fusion::deque</span></tt></a> if <a class="reference external" href="../../../../boost/fusion/container/deque/deque_fwd.hpp"><tt class="docutils literal">BOOST_FUSION_HAS_VARIADIC_DEQUE</tt></a> is defined
    7123. 

  7123. (by <a class="reference external" href="../../../fusion/doc/html/index.html">Boost.Fusion</a>), or <a class="reference external" href="../../../mpl/doc/refmanual/vector.html"><tt class="docutils literal"><span class="pre">boost::mpl::vector</span></tt></a> otherwise.</p>
    7124. 

  7124. <table class="docutils field-list" frame="void" rules="none">
    7125. 

  7125. <col class="field-name" />
    7126. 

  7126. <col class="field-body" />
    7127. 

  7127. <tbody valign="top">
    7128. 

  7128. <tr class="field"><th class="field-name">Example:</th><td class="field-body"></td>
    7129. 

  7129. </tr>
    7130. 

  7130. </tbody>
    7131. 

  7131. </table>
    7132. 

  7132. <pre class="literal-block">
    7133. 

  7133. #define BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE <a class="reference external" href="../../../fusion/doc/html/fusion/container/vector.html"><tt class="docutils literal"><span class="pre">boost::fusion::vector</span></tt></a>
    7134. 

  7134. </pre>
    7135. 

  7135. <table class="docutils field-list" frame="void" rules="none">
    7136. 

  7136. <col class="field-name" />
    7137. 

  7137. <col class="field-body" />
    7138. 

  7138. <tbody valign="top">
    7139. 

  7139. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/parameters.hpp">boost/parameter/parameters.hpp</a></td>
    7140. 

  7140. </tr>
    7141. 

  7141. </tbody>
    7142. 

  7142. </table>
    7143. 

  7143. </div>
    7144. 

  7144. <div class="section" id="id26">
    7145. 

  7145. <span id="boost-parameter-max-arity"></span><h2><a class="toc-backref" href="#id87">8.6&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_MAX_ARITY</tt></a></h2>
    7146. 

  7146. <p>If <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is <tt class="docutils literal">#defined</tt>, then:</p>
    7147. 

  7147. <ul class="simple">
    7148. 

  7148. <li>If the <a class="reference external" href="../../../mpl/doc/refmanual/variadic-sequence.html">MPL Variadic Sequence</a> underlying the nested <tt class="docutils literal">parameter_spec</tt>
    7149. 

  7149. type of <tt class="docutils literal">parameters</tt> does not have a size limit--which is the case with
    7150. 

  7150. <a class="reference external" href="../../../mp11/doc/html/mp11.html#mp_listt"><tt class="docutils literal"><span class="pre">boost::mp11::mp_list</span></tt></a>, <a class="reference external" href="../../../fusion/doc/html/fusion/container/list.html"><tt class="docutils literal"><span class="pre">boost::fusion::list</span></tt></a>, and <a class="reference external" href="../../../fusion/doc/html/fusion/container/deque.html"><tt class="docutils literal"><span class="pre">boost::fusion::deque</span></tt></a>, but not
    7151. 

  7151. <a class="reference external" href="../../../mpl/doc/refmanual/vector.html"><tt class="docutils literal"><span class="pre">boost::mpl::vector</span></tt></a>--then this macro can be safely ignored.  User code that
    7152. 

  7152. manually defines <a class="reference internal" href="#boost-parameter-variadic-mpl-sequence"><tt class="docutils literal">BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE</tt></a> should also
    7153. 

  7153. manually define this macro to the size limit of the sequence if it has
    7154. 

  7154. one.</li>
    7155. 

  7155. </ul>
    7156. 

  7156. <p>If <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is <strong>not</strong> <tt class="docutils literal">#defined</tt>, then:</p>
    7157. 

  7157. <ul class="simple">
    7158. 

  7158. <li>Mutable references must be wrapped by <a class="reference external" href="../../../core/doc/html/core/ref.html"><tt class="docutils literal"><span class="pre">boost::ref</span></tt></a> or <a class="reference external" href="http://en.cppreference.com/w/cpp/utility/functional/ref"><tt class="docutils literal"><span class="pre">std::ref</span></tt></a> if passed
    7159. 

  7159. by position to Boost.Parameter-enabled functions with arity greater than
    7160. 

  7160. or equal to <a class="reference internal" href="#boost-parameter-exponential-overload-threshold-arity"><tt class="docutils literal">BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY</tt></a>.</li>
    7161. 

  7161. </ul>
    7162. 

  7162. <table class="docutils field-list" frame="void" rules="none">
    7163. 

  7163. <col class="field-name" />
    7164. 

  7164. <col class="field-body" />
    7165. 

  7165. <tbody valign="top">
    7166. 

  7166. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/config.hpp">boost/parameter/config.hpp</a></td>
    7167. 

  7167. </tr>
    7168. 

  7168. <tr class="field"><th class="field-name">Default Value:</th><td class="field-body"><a class="reference external" href="../../../mpl/doc/refmanual/limit-vector-size.html"><tt class="docutils literal">BOOST_MPL_LIMIT_VECTOR_SIZE</tt></a> (defined by <a class="reference external" href="../../../mpl/doc/index.html">Boost.MPL</a>) if
    7169. 

  7169. perfect forwarding is supported, <tt class="docutils literal">8</tt> otherwise.</td>
    7170. 

  7170. </tr>
    7171. 

  7171. <tr class="field"><th class="field-name">Minimum Value:</th><td class="field-body"><tt class="docutils literal">2</tt></td>
    7172. 

  7172. </tr>
    7173. 

  7173. <tr class="field"><th class="field-name">Maximum Value:</th><td class="field-body"><a class="reference internal" href="#boost-parameter-compose-max-arity"><tt class="docutils literal">BOOST_PARAMETER_COMPOSE_MAX_ARITY</tt></a></td>
    7174. 

  7174. </tr>
    7175. 

  7175. </tbody>
    7176. 

  7176. </table>
    7177. 

  7177. </div>
    7178. 

  7178. <div class="section" id="id27">
    7179. 

  7179. <span id="boost-parameter-compose-max-arity"></span><h2><a class="toc-backref" href="#id88">8.7&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_COMPOSE_MAX_ARITY</tt></a></h2>
    7180. 

  7180. <p>If <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is <strong>not</strong> <tt class="docutils literal">#defined</tt>, then
    7181. 

  7181. determines the maximum number of arguments supported by the <tt class="docutils literal">compose</tt> function
    7182. 

  7182. and by the <a class="reference internal" href="#boost-parameter-no-spec-function"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_FUNCTION</tt></a>,
    7183. 

  7183. <a class="reference internal" href="#boost-parameter-no-spec-member-function"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION</tt></a>,
    7184. 

  7184. <a class="reference internal" href="#boost-parameter-no-spec-const-member-function"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION</tt></a>,
    7185. 

  7185. <a class="reference internal" href="#boost-parameter-no-spec-function-call-operator"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR</tt></a>,
    7186. 

  7186. <a class="reference internal" href="#boost-parameter-no-spec-const-function-call-operator"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR</tt></a>,
    7187. 

  7187. <a class="reference internal" href="#boost-parameter-no-spec-constructor"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR</tt></a>, and
    7188. 

  7188. <a class="reference internal" href="#boost-parameter-no-spec-no-base-constructor"><tt class="docutils literal">BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR</tt></a> code generation macros.</p>
    7189. 

  7189. <table class="docutils field-list" frame="void" rules="none">
    7190. 

  7190. <col class="field-name" />
    7191. 

  7191. <col class="field-body" />
    7192. 

  7192. <tbody valign="top">
    7193. 

  7193. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/config.hpp">boost/parameter/config.hpp</a></td>
    7194. 

  7194. </tr>
    7195. 

  7195. <tr class="field"><th class="field-name">Default Value:</th><td class="field-body"><tt class="docutils literal">20</tt> for a few older compilers, <tt class="docutils literal">64</tt> otherwise</td>
    7196. 

  7196. </tr>
    7197. 

  7197. <tr class="field"><th class="field-name">Minimum Value:</th><td class="field-body"><tt class="docutils literal">2</tt></td>
    7198. 

  7198. </tr>
    7199. 

  7199. </tbody>
    7200. 

  7200. </table>
    7201. 

  7201. </div>
    7202. 

  7202. <div class="section" id="id28">
    7203. 

  7203. <span id="boost-parameter-exponential-overload-threshold-arity"></span><h2><a class="toc-backref" href="#id89">8.8&nbsp;&nbsp;&nbsp;<tt class="docutils literal">BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY</tt></a></h2>
    7204. 

  7204. <p>If this library does <strong>not</strong> support perfect forwarding, determines the number
    7205. 

  7205. of arguments less than which <tt class="docutils literal">parameters</tt> generates an exponential number of
    7206. 

  7206. function call operator overloads, and greater than or equal to which
    7207. 

  7207. <tt class="docutils literal">parameters</tt> does not.  Will only be <tt class="docutils literal">#defined</tt> by the library if it is
    7208. 

  7208. not already <tt class="docutils literal">#defined</tt> and <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> is
    7209. 

  7209. <strong>not</strong> <tt class="docutils literal">#defined</tt>.</p>
    7210. 

  7210. <table class="docutils field-list" frame="void" rules="none">
    7211. 

  7211. <col class="field-name" />
    7212. 

  7212. <col class="field-body" />
    7213. 

  7213. <tbody valign="top">
    7214. 

  7214. <tr class="field"><th class="field-name">Defined in:</th><td class="field-body"><a class="reference external" href="../../../../boost/parameter/config.hpp">boost/parameter/config.hpp</a></td>
    7215. 

  7215. </tr>
    7216. 

  7216. <tr class="field"><th class="field-name">Default Value:</th><td class="field-body"><tt class="docutils literal">0</tt></td>
    7217. 

  7217. </tr>
    7218. 

  7218. <tr class="field"><th class="field-name">Minimum Value:</th><td class="field-body"><tt class="docutils literal">0</tt></td>
    7219. 

  7219. </tr>
    7220. 

  7220. </tbody>
    7221. 

  7221. </table>
    7222. 

  7222. </div>
    7223. 

  7223. <div class="section" id="outside-of-this-library">
    7224. 

  7224. <h2><a class="toc-backref" href="#id90">8.9&nbsp;&nbsp;&nbsp;...Outside Of This Library</a></h2>
    7225. 

  7225. <ol class="arabic simple">
    7226. 

  7226. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro
    7227. 

  7227. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__03_defects"><tt class="docutils literal">BOOST_NO_FUNCTION_TEMPLATE_ORDERING</tt></a>, then the macros
    7228. 

  7228. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> and
    7229. 

  7229. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined; otherwise, the
    7230. 

  7230. code generation macros would not work correctly.</li>
    7231. 

  7231. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__03_defects"><tt class="docutils literal">BOOST_NO_SFINAE</tt></a>, then the macros
    7232. 

  7232. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> and
    7233. 

  7233. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined; otherwise, keyword
    7234. 

  7234. types generated by <a class="reference internal" href="#boost-parameter-name"><tt class="docutils literal">BOOST_PARAMETER_NAME</tt></a> and
    7235. 

  7235. <a class="reference internal" href="#boost-parameter-nested-keyword"><tt class="docutils literal">BOOST_PARAMETER_NESTED_KEYWORD</tt></a> would not work correctly.</li>
    7236. 

  7236. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro
    7237. 

  7237. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_RVALUE_REFERENCES</tt></a>, then the macros
    7238. 

  7238. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> and
    7239. 

  7239. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7240. 

  7240. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_VARIADIC_TEMPLATES</tt></a>,
    7241. 

  7241. then the macros <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> and
    7242. 

  7242. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7243. 

  7243. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro
    7244. 

  7244. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS</tt></a>, then the macros
    7245. 

  7245. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a> and
    7246. 

  7246. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7247. 

  7247. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_CONSTEXPR</tt></a>, then the
    7248. 

  7248. macro <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7249. 

  7249. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_DECLTYPE_N3276</tt></a>,
    7250. 

  7250. then the macro <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7251. 

  7251. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_AUTO_DECLARATIONS</tt></a>,
    7252. 

  7252. then the macro <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7253. 

  7253. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_TEMPLATE_ALIASES</tt></a>,
    7254. 

  7254. then the macro <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7255. 

  7255. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_STATIC_ASSERT</tt></a>, then
    7256. 

  7256. the macro <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7257. 

  7257. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_HDR_TYPE_TRAITS</tt></a>,
    7258. 

  7258. then the macro <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7259. 

  7259. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro
    7260. 

  7260. <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_HDR_INITIALIZER_LIST</tt></a>, then the macro
    7261. 

  7261. <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7262. 

  7262. <li>If <a class="reference external" href="../../../config/doc/html/index.html">Boost.Config</a> defines the macro <a class="reference external" href="../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported"><tt class="docutils literal">BOOST_NO_CXX11_HDR_TUPLE</tt></a>, then the
    7263. 

  7263. macro <a class="reference internal" href="#boost-parameter-can-use-mp11"><tt class="docutils literal">BOOST_PARAMETER_CAN_USE_MP11</tt></a> will be left undefined.</li>
    7264. 

  7264. <li>If <a class="reference external" href="../../../fusion/doc/html/index.html">Boost.Fusion</a> defines the macro <a class="reference external" href="../../../../boost/fusion/container/list/list_fwd.hpp"><tt class="docutils literal">BOOST_FUSION_HAS_VARIADIC_LIST</tt></a>,
    7265. 

  7265. if this library defines the macro
    7266. 

  7266. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a>, and if
    7267. 

  7267. <a class="reference internal" href="#boost-parameter-variadic-mpl-sequence"><tt class="docutils literal">BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE</tt></a> is left undefined, then the
    7268. 

  7268. <a class="reference external" href="../../../mpl/doc/refmanual/variadic-sequence.html">MPL Variadic Sequence</a> underlying the nested <tt class="docutils literal">parameter_spec</tt> type of
    7269. 

  7269. <tt class="docutils literal">parameters</tt> will be <a class="reference external" href="../../../fusion/doc/html/fusion/container/list.html"><tt class="docutils literal"><span class="pre">boost::fusion::list</span></tt></a>.</li>
    7270. 

  7270. <li>If <a class="reference external" href="../../../fusion/doc/html/index.html">Boost.Fusion</a> defines the macro <a class="reference external" href="../../../../boost/fusion/container/deque/deque_fwd.hpp"><tt class="docutils literal">BOOST_FUSION_HAS_VARIADIC_DEQUE</tt></a>,
    7271. 

  7271. if this library defines the macro
    7272. 

  7272. <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a>, and if
    7273. 

  7273. <a class="reference internal" href="#boost-parameter-variadic-mpl-sequence"><tt class="docutils literal">BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE</tt></a> is left undefined, then the
    7274. 

  7274. <a class="reference external" href="../../../mpl/doc/refmanual/variadic-sequence.html">MPL Variadic Sequence</a> underlying the nested <tt class="docutils literal">parameter_spec</tt> type of
    7275. 

  7275. <tt class="docutils literal">parameters</tt> will be <a class="reference external" href="../../../fusion/doc/html/fusion/container/deque.html"><tt class="docutils literal"><span class="pre">boost::fusion::deque</span></tt></a>.</li>
    7276. 

  7276. <li>The value that <a class="reference external" href="../../../mpl/doc/index.html">Boost.MPL</a> defines the macro
    7277. 

  7277. <a class="reference external" href="../../../mpl/doc/refmanual/limit-vector-size.html"><tt class="docutils literal">BOOST_MPL_LIMIT_VECTOR_SIZE</tt></a> as will be the value that this library
    7278. 

  7278. defines the macro <a class="reference internal" href="#boost-parameter-max-arity"><tt class="docutils literal">BOOST_PARAMETER_MAX_ARITY</tt></a> as if this library defines
    7279. 

  7279. the macro <a class="reference internal" href="#boost-parameter-has-perfect-forwarding"><tt class="docutils literal">BOOST_PARAMETER_HAS_PERFECT_FORWARDING</tt></a>.</li>
    7280. 

  7280. </ol>
    7281. 

  7281. </div>
    7282. 

  7282. </div>
    7283. 

  7283. <div class="section" id="tutorial">
    7284. 

  7284. <h1><a class="toc-backref" href="#id91">9&nbsp;&nbsp;&nbsp;Tutorial</a></h1>
    7285. 

  7285. <p>Follow <a class="reference external" href="index.html#tutorial">this link</a> to the Boost.Parameter tutorial documentation.</p>
    7286. 

  7286. <hr class="docutils" />
    7287. 

  7287. <table class="docutils footnote" frame="void" id="thread" rules="none">
    7288. 

  7288. <colgroup><col class="label" /><col /></colgroup>
    7289. 

  7289. <tbody valign="top">
    7290. 

  7290. <tr><td class="label"><a class="fn-backref" href="#id2">[1]</a></td><td>References to tag objects may be initialized multiple
    7291. 

  7291. times.  This scenario can only occur in the presence of
    7292. 

  7292. threading.  Because the C++ standard doesn't consider threading,
    7293. 

  7293. it doesn't explicitly allow or forbid multiple initialization of
    7294. 

  7294. references.  That said, it's hard to imagine an implementation
    7295. 

  7295. where it could make a difference.</td></tr>
    7296. 

  7296. </tbody>
    7297. 

  7297. </table>
    7298. 

  7298. <table class="docutils footnote" frame="void" id="no-result-of" rules="none">
    7299. 

  7299. <colgroup><col class="label" /><col /></colgroup>
    7300. 

  7300. <tbody valign="top">
    7301. 

  7301. <tr><td class="label">[2]</td><td><em>(<a class="fn-backref" href="#id6">1</a>, <a class="fn-backref" href="#id12">2</a>, <a class="fn-backref" href="#id15">3</a>)</em> Where <a class="reference external" href="../../../utility/utility.htm#BOOST_NO_RESULT_OF"><tt class="docutils literal">BOOST_NO_RESULT_OF</tt></a> is <tt class="docutils literal">#defined</tt>,
    7302. 

  7302. <a class="reference external" href="../../../utility/utility.htm#result_of"><tt class="docutils literal"><span class="pre">boost::result_of</span></tt></a><tt class="docutils literal"><span class="pre">&lt;F()&gt;::type</span></tt> is replaced by <tt class="docutils literal"><span class="pre">F::result_type</span></tt>.</td></tr>
    7303. 

  7303. </tbody>
    7304. 

  7304. </table>
    7305. 

  7305. </div>
    7306. 

  7306. </div>
    7307. 

  7307. <div class="footer">
    7308. 

  7308. <hr class="footer" />
    7309. 

  7309. Generated on: 2019-12-10 00:22 UTC.
    7310. 

  7310. Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
    7311. 

  7311. 

  7312. </div>
    7313. 

  7313. </body>
    7314. 

  7314. </html>
    7315.