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    28. 

  28. <h2><span class="refentrytitle">Macro BOOST_CONTRACT_OLD_PTR_IF_COPYABLE</span></h2>
    29. 

  29. <p>BOOST_CONTRACT_OLD_PTR_IF_COPYABLE &#8212; Program old values that can be completely disabled at compile-time for old value types that are not required to be copyable. </p>
    30. 

  30. </div>
    31. 

  31. <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
    32. 

  32. <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="reference.html#header.boost.contract_macro_hpp" title="Header &lt;boost/contract_macro.hpp&gt;">boost/contract_macro.hpp</a>&gt;
    33. 

  33. 

  34. </span>BOOST_CONTRACT_OLD_PTR_IF_COPYABLE(...)</pre></div>
    35. 

  35. <div class="refsect1">
    36. 

  36. <a name="idm45707992820784"></a><h2>Description</h2>
    37. 

  37. <p>This is used to program old value copies for types that might or might not be copyable:</p>
    38. 

  38. <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="comment">// Type `T` might or not be copyable.</span>
    39. 

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

  40. <span class="keyword">public</span><span class="special">:</span>
    41. 

  41.     <span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="special">...</span><span class="special">)</span> <span class="special">{</span>
    42. 

  42.         <span class="identifier">BOOST_CONTRACT_OLD_PTR_IF_COPYABLE</span><span class="special">(</span><span class="identifier">old_type_a</span><span class="special">)</span><span class="special">(</span><span class="identifier">old_var_a</span><span class="special">)</span><span class="special">;</span>
    43. 

  43.         <span class="identifier">BOOST_CONTRACT_OLD_PTR_IF_COPYABLE</span><span class="special">(</span><span class="identifier">old_type_b</span><span class="special">)</span><span class="special">(</span><span class="identifier">old_var_b</span><span class="special">,</span>
    44. 

  44.                 <span class="identifier">old_expr_b</span><span class="special">)</span><span class="special">;</span>
    45. 

  45.         <span class="identifier">BOOST_CONTRACT_PUBLIC_FUNCTION</span><span class="special">(</span><span class="keyword">this</span><span class="special">)</span>
    46. 

  46.             <span class="special">...</span>
    47. 

  47.             <span class="identifier">BOOST_CONTRACT_OLD</span><span class="special">(</span><span class="special">[</span><span class="special">&amp;</span><span class="special">]</span> <span class="special">{</span>
    48. 

  48.                 <span class="identifier">old_var_a</span> <span class="special">=</span> <span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">old_expr_a</span><span class="special">)</span><span class="special">;</span>
    49. 

  49.                 <span class="special">...</span>
    50. 

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

  51.             <span class="special">...</span> <span class="comment">// In postconditions or exception guarantees:</span>
    52. 

  52.                 <span class="keyword">if</span><span class="special">(</span><span class="identifier">old_var_a</span><span class="special">)</span> <span class="special">...</span> <span class="comment">// Always null for non-copyable types.</span>
    53. 

  53.                 <span class="keyword">if</span><span class="special">(</span><span class="identifier">old_var_b</span><span class="special">)</span> <span class="special">...</span> <span class="comment">// Always null for non-copyable types.</span>
    54. 

  54.             <span class="special">...</span>
    55. 

  55.         <span class="special">;</span>
    56. 

  56. 

  57.         <span class="special">...</span> <span class="comment">// Function body.</span>
    58. 

  58.     <span class="special">}</span>
    59. 

  59. 

  60.     <span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">g</span><span class="special">(</span><span class="special">...</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">virtual_</span><span class="special">*</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> <span class="special">{</span>
    61. 

  61.         <span class="identifier">BOOST_CONTRACT_OLD_PTR_IF_COPYABLE</span><span class="special">(</span><span class="identifier">old_type_a</span><span class="special">)</span><span class="special">(</span><span class="identifier">old_var_a</span><span class="special">)</span><span class="special">;</span>
    62. 

  62.         <span class="identifier">BOOST_CONTRACT_OLD_PTR_IF_COPYABLE</span><span class="special">(</span><span class="identifier">old_type_b</span><span class="special">)</span><span class="special">(</span><span class="identifier">v</span><span class="special">,</span> <span class="identifier">old_var_b</span><span class="special">,</span>
    63. 

  63.                 <span class="identifier">old_expr_b</span><span class="special">)</span><span class="special">;</span>
    64. 

  64.         <span class="identifier">BOOST_CONTRACT_PUBLIC_FUNCTION</span><span class="special">(</span><span class="identifier">v</span><span class="special">,</span> <span class="keyword">this</span><span class="special">)</span>
    65. 

  65.             <span class="special">...</span>
    66. 

  66.             <span class="identifier">BOOST_CONTRACT_OLD</span><span class="special">(</span><span class="special">[</span><span class="special">&amp;</span><span class="special">]</span> <span class="special">{</span>
    67. 

  67.                 <span class="identifier">old_var_a</span> <span class="special">=</span> <span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">v</span><span class="special">,</span> <span class="identifier">old_expr_a</span><span class="special">)</span><span class="special">;</span>
    68. 

  68.                 <span class="special">...</span>
    69. 

  69.             <span class="special">}</span><span class="special">)</span>
    70. 

  70.             <span class="special">...</span> <span class="comment">// In postconditions or exception guarantees:</span>
    71. 

  71.                 <span class="keyword">if</span><span class="special">(</span><span class="identifier">old_var_a</span><span class="special">)</span> <span class="special">...</span> <span class="comment">// Always null for non-copyable types.</span>
    72. 

  72.                 <span class="keyword">if</span><span class="special">(</span><span class="identifier">old_var_b</span><span class="special">)</span> <span class="special">...</span> <span class="comment">// Always null for non-copyable types.</span>
    73. 

  73.             <span class="special">...</span>
    74. 

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

  75. 

  76.         <span class="special">...</span> <span class="comment">// Function body.</span>
    77. 

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

  78. 

  79.     <span class="special">...</span>
    80. 

  80. <span class="special">}</span><span class="special">;</span>
    81. 

  81. </pre>
    82. 

  82. <p>This is an overloaded variadic macro and it can be used in the following different ways (note that no code is generated when  <code class="computeroutput"><a class="link" href="BOOST_CONTRACT_NO_OLDS.html" title="Macro BOOST_CONTRACT_NO_OLDS">BOOST_CONTRACT_NO_OLDS</a></code> is defined).</p>
    83. 

  83. <p>1. <code class="computeroutput">BOOST_CONTRACT_OLD_PTR_IF_COPYABLE(old_type)(old_var)</code> expands to code equivalent to the following (this leaves the old value pointer null):</p>
    84. 

  84. <pre class="programlisting"><span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_CONTRACT_NO_OLDS</span>
    85. 

  85.     <span class="comment">// This declaration does not need to use `v`.</span>
    86. 

  86.     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">old_ptr_if_copyable</span><span class="special">&lt;</span><span class="identifier">old_type</span><span class="special">&gt;</span> <span class="identifier">old_var</span>
    87. 

  87. <span class="preprocessor">#endif</span>
    88. 

  88. </pre>
    89. 

  89. <p>2. <code class="computeroutput">BOOST_CONTRACT_OLD_PTR_IF_COPYABLE(old_type)(old_var, old_expr)</code> expands to code equivalent to the following (this initializes the pointer to the old value copy, but not to be used for virtual public functions and public function overrides):</p>
    90. 

  90. <pre class="programlisting"><span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_CONTRACT_NO_OLDS</span>
    91. 

  91.     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">old_ptr_if_copyable</span><span class="special">&lt;</span><span class="identifier">old_type</span><span class="special">&gt;</span> <span class="identifier">old_var</span> <span class="special">=</span>
    92. 

  92.             <span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">old_expr</span><span class="special">)</span>
    93. 

  93. <span class="preprocessor">#endif</span>
    94. 

  94. </pre>
    95. 

  95. <p>3. <code class="computeroutput">BOOST_CONTRACT_OLD_PTR_IF_COPYABLE(old_type)(v, old_var, old_expr)</code> expands to code equivalent to the following (this initializes the pointer to the old value copy for virtual public functions and public function overrides):</p>
    96. 

  96. <pre class="programlisting"><span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_CONTRACT_NO_OLDS</span>
    97. 

  97.     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">old_ptr_if_copyable</span><span class="special">&lt;</span><span class="identifier">old_type</span><span class="special">&gt;</span> <span class="identifier">old_var</span> <span class="special">=</span>
    98. 

  98.             <span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">v</span><span class="special">,</span> <span class="identifier">old_expr</span><span class="special">)</span>
    99. 

  99. <span class="preprocessor">#endif</span>
    100. 

  100. </pre>
    101. 

  101. <p>Where:</p>
    102. 

  102. <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
    103. 

  103. <li class="listitem"><p><code class="computeroutput"><span class="bold"><strong>old_type</strong></span></code> is the type of the pointed old value. If this type is not copyable (i.e., <code class="computeroutput">boost::contract::is_old_value_copyable&lt;old_type&gt;::value</code> is <code class="computeroutput">false</code>), this pointer will always be null, but this library will not generate a compile-time error when this pointer is dereferenced (see <code class="computeroutput"><a class="link" href="BOOST_CONTRACT_OLD_PTR.html" title="Macro BOOST_CONTRACT_OLD_PTR">BOOST_CONTRACT_OLD_PTR</a></code>). (This is a variadic macro parameter so it can contain commas not protected by round parenthesis.) </p></li>
    104. 

  104. <li class="listitem"><p><code class="computeroutput"><span class="bold"><strong>v</strong></span></code> is the extra trailing parameter of type  <code class="computeroutput"><a class="link" href="boost/contract/virtual_.html" title="Class virtual_">boost::contract::virtual_</a></code><code class="computeroutput">*</code> and default value <code class="computeroutput">0</code> from the enclosing virtual public function or public function override declaring the contract. (This is not a variadic macro parameter but it should never contain commas because it is an identifier.) </p></li>
    105. 

  105. <li class="listitem"><p><code class="computeroutput"><span class="bold"><strong>old_var</strong></span></code> is the name of the old value pointer variable. (This is not a variadic macro parameter but it should never contain commas because it is an identifier.) </p></li>
    106. 

  106. <li class="listitem"><p><code class="computeroutput"><span class="bold"><strong>old_expr</strong></span></code> is the expression to be evaluated and copied in the old value pointer. (This is not a variadic macro parameter so any comma it might contain must be protected by round parenthesis and <code class="computeroutput">BOOST_CONTRACT_OLD_PTR_IF_COPYABLE(old_type)(v, old_var, (old_expr))</code> will always work.)</p></li>
    107. 

  107. </ul></div>
    108. 

  108. <p>
    109. 

  109. </p>
    110. 

  110. <p><span class="bold"><strong>See Also:</strong></span></p>
    111. 

  111. <p> <a class="link" href="boost_contract/extras.html#boost_contract.extras.disable_contract_compilation__macro_interface_" title="Disable Contract Compilation (Macro Interface)">
    112. 

  112.         Disable Contract Compilation</a>,  <a class="link" href="boost_contract/extras.html#boost_contract.extras.old_value_requirements__templates_" title="Old Value Requirements (Templates)">
    113. 

  113.         Old Value Requirements</a> </p>
    114. 

  114. <p>
    115. 

  115. </p>
    116. 

  116. <p>
    117. 

  117. </p>
    118. 

  118. </div>
    119. 

  119. </div>
    120. 

  120. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
    121. 

  121. <td align="left"></td>
    122. 

  122. <td align="right"><div class="copyright-footer">Copyright &#169; 2008-2019 Lorenzo Caminiti<p>
    123. 

  123.         Distributed under the Boost Software License, Version 1.0 (see accompanying
    124. 

  124.         file LICENSE_1_0.txt or a copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
    125. 

  125.       </p>
    126. 

  126. </div></td>
    127. 

  127. </tr></table>
    128. 

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    129. 

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