Home Explore Help
Register Sign In
devn00b
/
EQ2EMu
9
3
Fork 0
Files Issues 59
Tree: 9d9a5ec294
Branches Tags
EQ2EMu
/
EQ2
/
source
/
depends
/
boost_1_72_0
/
libs
/
optional
/
doc
/
html
/
boost_optional
/
tutorial
/
in_place_factories.html

in_place_factories.html 19 KB
History Raw

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197 
  1. <html>
    2. 

  2. <head>
    3. 

  3. <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
    4. 

  4. <title>In-Place Factories</title>
    5. 

  5. <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
    6. 

  6. <meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
    7. 

  7. <link rel="home" href="../../index.html" title="Boost.Optional">
    8. 

  8. <link rel="up" href="../../optional/tutorial.html" title="Tutorial">
    9. 

  9. <link rel="prev" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">
    10. 

  10. <link rel="next" href="gotchas.html" title="Gotchas">
    11. 

  11. </head>
    12. 

  12. <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
    13. 

  13. <table cellpadding="2" width="100%"><tr>
    14. 

  14. <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
    15. 

  15. <td align="center"><a href="../../../../../../index.html">Home</a></td>
    16. 

  16. <td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
    17. 

  17. <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
    18. 

  18. <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
    19. 

  19. <td align="center"><a href="../../../../../../more/index.htm">More</a></td>
    20. 

  20. </tr></table>
    21. 

  21. <hr>
    22. 

  22. <div class="spirit-nav">
    23. 

  23. <a accesskey="p" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
    24. 

  24. </div>
    25. 

  25. <div class="section">
    26. 

  26. <div class="titlepage"><div><div><h3 class="title">
    27. 

  27. <a name="boost_optional.tutorial.in_place_factories"></a><a class="link" href="in_place_factories.html" title="In-Place Factories">In-Place
    28. 

  28.       Factories</a>
    29. 

  29. </h3></div></div></div>
    30. 

  30. <p>
    31. 

  31.         One of the typical problems with wrappers and containers is that their interfaces
    32. 

  32.         usually provide an operation to initialize or assign the contained object
    33. 

  33.         as a copy of some other object. This not only requires the underlying type
    34. 

  34.         to be <a href="../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a>, but also requires
    35. 

  35.         the existence of a fully constructed object, often temporary, just to follow
    36. 

  36.         the copy from:
    37. 

  37.       </p>
    38. 

  38. <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span>
    39. 

  39. <span class="special">{</span>
    40. 

  40.     <span class="identifier">X</span> <span class="special">(</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span>
    41. 

  41. <span class="special">}</span> <span class="special">;</span>
    42. 

  42. 

  43. <span class="keyword">class</span> <span class="identifier">W</span>
    44. 

  44. <span class="special">{</span>
    45. 

  45.     <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
    46. 

  46. 

  47.     <span class="keyword">public</span><span class="special">:</span>
    48. 

  48. 

  49.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
    50. 

  50. <span class="special">}</span> <span class="special">;</span>
    51. 

  51. 

  52. <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
    53. 

  53. <span class="special">{</span>
    54. 

  54.     <span class="comment">// Temporary object created.</span>
    55. 

  55.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span><span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
    56. 

  56. <span class="special">}</span>
    57. 

  57. </pre>
    58. 

  58. <p>
    59. 

  59.         A solution to this problem is to support direct construction of the contained
    60. 

  60.         object right in the container's storage. In this scheme, the user only needs
    61. 

  61.         to supply the arguments to the constructor to use in the wrapped object construction.
    62. 

  62.       </p>
    63. 

  63. <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
    64. 

  64. <span class="special">{</span>
    65. 

  65.     <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
    66. 

  66. 

  67.     <span class="keyword">public</span><span class="special">:</span>
    68. 

  68. 

  69.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
    70. 

  70.     <span class="identifier">W</span> <span class="special">(</span> <span class="keyword">int</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">a1</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">a0</span><span class="special">,</span><span class="identifier">a1</span><span class="special">)</span> <span class="special">{}</span>
    71. 

  71. <span class="special">}</span> <span class="special">;</span>
    72. 

  72. 

  73. <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
    74. 

  74. <span class="special">{</span>
    75. 

  75.     <span class="comment">// Wrapped object constructed in-place</span>
    76. 

  76.     <span class="comment">// No temporary created.</span>
    77. 

  77.     <span class="identifier">W</span> <span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">;</span>
    78. 

  78. <span class="special">}</span>
    79. 

  79. </pre>
    80. 

  80. <p>
    81. 

  81.         A limitation of this method is that it doesn't scale well to wrapped objects
    82. 

  82.         with multiple constructors nor to generic code were the constructor overloads
    83. 

  83.         are unknown.
    84. 

  84.       </p>
    85. 

  85. <p>
    86. 

  86.         The solution presented in this library is the family of <span class="bold"><strong>InPlaceFactories</strong></span>
    87. 

  87.         and <span class="bold"><strong>TypedInPlaceFactories</strong></span>. These factories
    88. 

  88.         are a family of classes which encapsulate an increasing number of arbitrary
    89. 

  89.         constructor parameters and supply a method to construct an object of a given
    90. 

  90.         type using those parameters at an address specified by the user via placement
    91. 

  91.         new.
    92. 

  92.       </p>
    93. 

  93. <p>
    94. 

  94.         For example, one member of this family looks like:
    95. 

  95.       </p>
    96. 

  96. <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">A1</span><span class="special">&gt;</span>
    97. 

  97. <span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory2</span>
    98. 

  98. <span class="special">{</span>
    99. 

  99.     <span class="identifier">A0</span> <span class="identifier">m_a0</span> <span class="special">;</span> <span class="identifier">A1</span> <span class="identifier">m_a1</span> <span class="special">;</span>
    100. 

  100. 

  101.     <span class="keyword">public</span><span class="special">:</span>
    102. 

  102. 

  103.     <span class="identifier">TypedInPlaceFactory2</span><span class="special">(</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">A1</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a1</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">m_a0</span><span class="special">(</span><span class="identifier">a0</span><span class="special">),</span> <span class="identifier">m_a1</span><span class="special">(</span><span class="identifier">a1</span><span class="special">)</span> <span class="special">{}</span>
    104. 

  104. 

  105.     <span class="keyword">void</span> <span class="identifier">construct</span> <span class="special">(</span> <span class="keyword">void</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">)</span> <span class="special">{</span> <span class="keyword">new</span> <span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="identifier">T</span><span class="special">(</span><span class="identifier">m_a0</span><span class="special">,</span><span class="identifier">m_a1</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
    106. 

  106.  <span class="special">}</span> <span class="special">;</span>
    107. 

  107. </pre>
    108. 

  108. <p>
    109. 

  109.         A wrapper class aware of this can use it as:
    110. 

  110.       </p>
    111. 

  111. <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
    112. 

  112. <span class="special">{</span>
    113. 

  113.     <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
    114. 

  114. 

  115.     <span class="keyword">public</span><span class="special">:</span>
    116. 

  116. 

  117.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
    118. 

  118.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory2</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">fac</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">fac</span><span class="special">.</span><span class="identifier">construct</span><span class="special">(&amp;</span><span class="identifier">wrapped_</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
    119. 

  119. <span class="special">}</span> <span class="special">;</span>
    120. 

  120. 

  121. <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
    122. 

  122. <span class="special">{</span>
    123. 

  123.     <span class="comment">// Wrapped object constructed in-place via a TypedInPlaceFactory.</span>
    124. 

  124.     <span class="comment">// No temporary created.</span>
    125. 

  125.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory2</span><span class="special">&lt;</span><span class="identifier">X</span><span class="special">,</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">))</span> <span class="special">;</span>
    126. 

  126. <span class="special">}</span>
    127. 

  127. </pre>
    128. 

  128. <p>
    129. 

  129.         The factories are divided in two groups:
    130. 

  130.       </p>
    131. 

  131. <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
    132. 

  132. <li class="listitem">
    133. 

  133.             <span class="underline">TypedInPlaceFactories</span>: those which
    134. 

  134.             take the target type as a primary template parameter.
    135. 

  135.           </li>
    136. 

  136. <li class="listitem">
    137. 

  137.             <span class="underline">InPlaceFactories</span>: those with a
    138. 

  138.             template <code class="computeroutput"><span class="identifier">construct</span><span class="special">(</span><span class="keyword">void</span><span class="special">*)</span></code>
    139. 

  139.             member function taking the target type.
    140. 

  140.           </li>
    141. 

  141. </ul></div>
    142. 

  142. <p>
    143. 

  143.         Within each group, all the family members differ only in the number of parameters
    144. 

  144.         allowed.
    145. 

  145.       </p>
    146. 

  146. <p>
    147. 

  147.         This library provides an overloaded set of helper template functions to construct
    148. 

  148.         these factories without requiring unnecessary template parameters:
    149. 

  149.       </p>
    150. 

  150. <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,...,</span><span class="keyword">class</span> <span class="identifier">AN</span><span class="special">&gt;</span>
    151. 

  151. <span class="identifier">InPlaceFactoryN</span> <span class="special">&lt;</span><span class="identifier">A0</span><span class="special">,...,</span><span class="identifier">AN</span><span class="special">&gt;</span> <span class="identifier">in_place</span> <span class="special">(</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">AN</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">aN</span><span class="special">)</span> <span class="special">;</span>
    152. 

  152. 

  153. <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,...,</span><span class="keyword">class</span> <span class="identifier">AN</span><span class="special">&gt;</span>
    154. 

  154. <span class="identifier">TypedInPlaceFactoryN</span> <span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">A0</span><span class="special">,...,</span><span class="identifier">AN</span><span class="special">&gt;</span> <span class="identifier">in_place</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">AN</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">aN</span><span class="special">)</span> <span class="special">;</span>
    155. 

  155. </pre>
    156. 

  156. <p>
    157. 

  157.         In-place factories can be used generically by the wrapper and user as follows:
    158. 

  158.       </p>
    159. 

  159. <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
    160. 

  160. <span class="special">{</span>
    161. 

  161.     <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
    162. 

  162. 

  163.     <span class="keyword">public</span><span class="special">:</span>
    164. 

  164. 

  165.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
    166. 

  166. 

  167.     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">InPlaceFactory</span> <span class="special">&gt;</span>
    168. 

  168.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">fac</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">fac</span><span class="special">.</span><span class="keyword">template</span> <span class="special">&lt;</span><span class="identifier">X</span><span class="special">&gt;</span><span class="identifier">construct</span><span class="special">(&amp;</span><span class="identifier">wrapped_</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
    169. 

  169. 

  170. <span class="special">}</span> <span class="special">;</span>
    171. 

  171. 

  172. <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
    173. 

  173. <span class="special">{</span>
    174. 

  174.     <span class="comment">// Wrapped object constructed in-place via a InPlaceFactory.</span>
    175. 

  175.     <span class="comment">// No temporary created.</span>
    176. 

  176.     <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">in_place</span><span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
    177. 

  177. <span class="special">}</span>
    178. 

  178. </pre>
    179. 

  179. <p>
    180. 

  180.         The factories are implemented in the headers: <a href="../../../../../../boost/utility/in_place_factory.hpp" target="_top">in_place_factory.hpp</a>
    181. 

  181.         and <a href="../../../../../../boost/utility/typed_in_place_factory.hpp" target="_top">typed_in_place_factory.hpp</a>
    182. 

  182.       </p>
    183. 

  183. </div>
    184. 

  184. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
    185. 

  185. <td align="left"></td>
    186. 

  186. <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014-2018 Andrzej Krzemie&#324;ski<p>
    187. 

  187.         Distributed under the Boost Software License, Version 1.0. (See accompanying
    188. 

  188.         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
    189. 

  189.       </p>
    190. 

  190. </div></td>
    191. 

  191. </tr></table>
    192. 

  192. <hr>
    193. 

  193. <div class="spirit-nav">
    194. 

  194. <a accesskey="p" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
    195. 

  195. </div>
    196. 

  196. </body>
    197. 

  197. </html>
    198.