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  25 <div class="refentry">
  26 <a name="boost.contract.old_ptr_if_copyable"></a><div class="titlepage"></div>
  27 <div class="refnamediv">
  28 <h2><span class="refentrytitle">Class template old_ptr_if_copyable</span></h2>
  29 <p>boost::contract::old_ptr_if_copyable &#8212; Old value pointer that does not require the pointed old value type to be copyable. </p>
  30 </div>
  31 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  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.old_hpp" title="Header &lt;boost/contract/old.hpp&gt;">boost/contract/old.hpp</a>&gt;
  33
  34 </span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> T<span class="special">&gt;</span>
  35 <span class="keyword">class</span> <a class="link" href="old_ptr_if_copyable.html" title="Class template old_ptr_if_copyable">old_ptr_if_copyable</a> <span class="special">{</span>
  36 <span class="keyword">public</span><span class="special">:</span>
  37   <span class="comment">// types</span>
  38   <span class="keyword">typedef</span> <span class="identifier">T</span> <a name="boost.contract.old_ptr_if_copyable.element_type"></a><span class="identifier">element_type</span><span class="special">;</span>  <span class="comment">// Pointed old value type. </span>
  39
  40   <span class="comment">// <a class="link" href="old_ptr_if_copyable.html#boost.contract.old_ptr_if_copyableconstruct-copy-destruct">construct/copy/destruct</a></span>
  41   <a class="link" href="old_ptr_if_copyable.html#idm45394999013184-bb"><span class="identifier">old_ptr_if_copyable</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
  42   <a class="link" href="old_ptr_if_copyable.html#idm45394999012576-bb"><span class="identifier">old_ptr_if_copyable</span></a><span class="special">(</span><a class="link" href="old_ptr.html" title="Class template old_ptr">old_ptr</a><span class="special">&lt;</span> <span class="identifier">T</span> <span class="special">&gt;</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  43
  44   <span class="comment">// <a class="link" href="old_ptr_if_copyable.html#idm45394999028256-bb">public member functions</a></span>
  45   <span class="identifier">T</span> <span class="keyword">const</span>  <span class="special">&amp;</span> <a class="link" href="old_ptr_if_copyable.html#idm45394999027696-bb"><span class="keyword">operator</span> <span class="special">*</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  46   <span class="identifier">T</span> <span class="keyword">const</span>  <span class="special">*</span> <a class="link" href="old_ptr_if_copyable.html#idm45394999022096-bb"><span class="keyword">operator</span><span class="special">-&gt;</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  47   <span class="keyword">explicit</span> <a class="link" href="old_ptr_if_copyable.html#idm45394999016496-bb"><span class="keyword">operator</span> <span class="keyword">bool</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  48 <span class="special">}</span><span class="special">;</span></pre></div>
  49 <div class="refsect1">
  50 <a name="idm45707994520144"></a><h2>Description</h2>
  51 <p>This pointer can be set to point to an actual old value copy using either  <code class="computeroutput"><a class="link" href="../../BOOST_CONTRACT_OLDOF.html" title="Macro BOOST_CONTRACT_OLDOF">BOOST_CONTRACT_OLDOF</a></code> or <code class="computeroutput"><a class="link" href="make_old_idm45394998968720.html" title="Function make_old">boost::contract::make_old</a></code>:</p>
  52 <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>
  53 <span class="keyword">class</span> <span class="identifier">u</span> <span class="special">{</span>
  54 <span class="keyword">public</span><span class="special">:</span>
  55     <span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">f</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>
  56         <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">T</span><span class="special">&gt;</span> <span class="identifier">old_var</span> <span class="special">=</span>
  57                 <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><span class="special">;</span>
  58         <span class="special">...</span>
  59             <span class="keyword">if</span><span class="special">(</span><span class="identifier">old_var</span><span class="special">)</span> <span class="special">...</span> <span class="comment">// Always null for non-copyable types.</span>
  60         <span class="special">...</span>
  61     <span class="special">}</span>
  62
  63     <span class="special">...</span>
  64 <span class="special">}</span><span class="special">;</span>
  65 </pre>
  66 <p><span class="bold"><strong>See Also:</strong></span></p>
  67 <p> <a class="link" href="../../boost_contract/extras.html#boost_contract.extras.old_value_requirements__templates_" title="Old Value Requirements (Templates)">
  68         Old Value Requirements</a></p>
  69 <p>
  70 </p>
  71 <p>
  72
  73 </p>
  74 <div class="refsect2">
  75 <a name="idm45707994479808"></a><h3>Template Parameters</h3>
  76 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
  77 <pre class="literallayout"><span class="keyword">typename</span> T</pre>
  78 <p>Type of the pointed old value. If this type is not copyable (i.e., <code class="computeroutput">boost::contract::is_old_value_copyable&lt;T&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). </p>
  79 </li></ol></div>
  80 </div>
  81 <div class="refsect2">
  82 <a name="idm45707994475104"></a><h3>
  83 <a name="boost.contract.old_ptr_if_copyableconstruct-copy-destruct"></a><code class="computeroutput">old_ptr_if_copyable</code>
  84         public
  85        construct/copy/destruct</h3>
  86 <div class="orderedlist"><ol class="orderedlist" type="1">
  87 <li class="listitem">
  88 <pre class="literallayout"><a name="idm45394999013184-bb"></a><span class="identifier">old_ptr_if_copyable</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>Construct this old value pointer as null. </li>
  89 <li class="listitem">
  90 <pre class="literallayout"><a name="idm45394999012576-bb"></a><span class="identifier">old_ptr_if_copyable</span><span class="special">(</span><a class="link" href="old_ptr.html" title="Class template old_ptr">old_ptr</a><span class="special">&lt;</span> <span class="identifier">T</span> <span class="special">&gt;</span> <span class="keyword">const</span> <span class="special">&amp;</span> other<span class="special">)</span><span class="special">;</span></pre>Construct this old value pointer from an old value pointer that requires the old value type to be copyable. <p>Ownership of the pointed value object is transferred to this pointer. This constructor is implicitly called by this library when assigning an object of this type using <code class="computeroutput"><code class="computeroutput"><a class="link" href="../../BOOST_CONTRACT_OLDOF.html" title="Macro BOOST_CONTRACT_OLDOF">BOOST_CONTRACT_OLDOF</a></code></code> (this constructor is usually not explicitly called by user code).</p>
  91 <p>
  92 </p>
  93 <div class="variablelist"><table border="0" class="variablelist compact">
  94 <colgroup>
  95 <col align="left" valign="top">
  96 <col>
  97 </colgroup>
  98 <tbody><tr>
  99 <td><p><span class="term">Parameters:</span></p></td>
 100 <td><div class="variablelist"><table border="0" class="variablelist compact">
 101 <colgroup>
 102 <col align="left" valign="top">
 103 <col>
 104 </colgroup>
 105 <tbody><tr>
 106 <td><p><span class="term"><code class="computeroutput">other</code></span></p></td>
 107 <td><p>Old value pointer that requires the old value type to be copyable. </p></td>
 108 </tr></tbody>
 109 </table></div></td>
 110 </tr></tbody>
 111 </table></div>
 112 </li>
 113 </ol></div>
 114 </div>
 115 <div class="refsect2">
 116 <a name="idm45707994455568"></a><h3>
 117 <a name="idm45394999028256-bb"></a><code class="computeroutput">old_ptr_if_copyable</code> public member functions</h3>
 118 <div class="orderedlist"><ol class="orderedlist" type="1">
 119 <li class="listitem">
 120 <pre class="literallayout"><span class="identifier">T</span> <span class="keyword">const</span>  <span class="special">&amp;</span> <a name="idm45394999027696-bb"></a><span class="keyword">operator</span> <span class="special">*</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>Dereference this old value pointer. <p>This will generate a run-time error if this pointer is null, but no compile-time error is generated if the pointed type <code class="computeroutput">T</code> is not copyable (i.e., if <code class="computeroutput">boost::contract::is_old_value_copyable&lt;T&gt;::value</code> is <code class="computeroutput">false</code>).</p>
 121 <p>
 122 </p>
 123 <div class="variablelist"><table border="0" class="variablelist compact">
 124 <colgroup>
 125 <col align="left" valign="top">
 126 <col>
 127 </colgroup>
 128 <tbody><tr>
 129 <td><p><span class="term">Returns:</span></p></td>
 130 <td><p>The pointed old value. Contract assertions should not change the state of the program so this member function is <code class="computeroutput">const</code> and it returns the old value as a reference to a constant object (see  <a class="link" href="../../boost_contract/contract_programming_overview.html#boost_contract.contract_programming_overview.constant_correctness" title="Constant-Correctness">
 131         Constant Correctness</a>). </p></td>
 132 </tr></tbody>
 133 </table></div>
 134 </li>
 135 <li class="listitem">
 136 <pre class="literallayout"><span class="identifier">T</span> <span class="keyword">const</span>  <span class="special">*</span> <a name="idm45394999022096-bb"></a><span class="keyword">operator</span><span class="special">-&gt;</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>Structure-dereference this old value pointer. <p>This will return null but will not generate a compile-time error if the pointed type <code class="computeroutput">T</code> is not copyable (i.e., if <code class="computeroutput">boost::contract::is_old_value_copyable&lt;T&gt;::value</code> is <code class="computeroutput">false</code>).</p>
 137 <p>
 138 </p>
 139 <div class="variablelist"><table border="0" class="variablelist compact">
 140 <colgroup>
 141 <col align="left" valign="top">
 142 <col>
 143 </colgroup>
 144 <tbody><tr>
 145 <td><p><span class="term">Returns:</span></p></td>
 146 <td><p>A pointer to the old value (null if this old value pointer is null). Contract assertions should not change the state of the program so this member function is <code class="computeroutput">const</code> and it returns the old value as a pointer to a constant object (see  <a class="link" href="../../boost_contract/contract_programming_overview.html#boost_contract.contract_programming_overview.constant_correctness" title="Constant-Correctness">
 147         Constant Correctness</a>). </p></td>
 148 </tr></tbody>
 149 </table></div>
 150 </li>
 151 <li class="listitem">
 152 <pre class="literallayout"><span class="keyword">explicit</span> <a name="idm45394999016496-bb"></a><span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>Query if this old value pointer is null or not (safe-bool operator). <p>(This is implemented using safe-bool emulation on compilers that do not support C++11 explicit type conversion operators.)</p>
 153 <p>
 154 </p>
 155 <div class="variablelist"><table border="0" class="variablelist compact">
 156 <colgroup>
 157 <col align="left" valign="top">
 158 <col>
 159 </colgroup>
 160 <tbody><tr>
 161 <td><p><span class="term">Returns:</span></p></td>
 162 <td><p>True if this pointer is not null, false otherwise. </p></td>
 163 </tr></tbody>
 164 </table></div>
 165 </li>
 166 </ol></div>
 167 </div>
 168 </div>
 169 </div>
 170 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 171 <td align="left"></td>
 172 <td align="right"><div class="copyright-footer">Copyright &#169; 2008-2019 Lorenzo Caminiti<p>
 173         Distributed under the Boost Software License, Version 1.0 (see accompanying
 174         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>)
 175       </p>
 176 </div></td>
 177 </tr></table>
 178 <hr>
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