1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Class template old_ptr</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Chapter 1. Boost.Contract 1.0.0"> 8<link rel="up" href="../../reference.html#header.boost.contract.old_hpp" title="Header <boost/contract/old.hpp>"> 9<link rel="prev" href="old_pointer.html" title="Class old_pointer"> 10<link rel="next" href="old_ptr_if_copyable.html" title="Class template old_ptr_if_copyable"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="old_pointer.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../reference.html#header.boost.contract.old_hpp"><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="old_ptr_if_copyable.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="refentry"> 26<a name="boost.contract.old_ptr"></a><div class="titlepage"></div> 27<div class="refnamediv"> 28<h2><span class="refentrytitle">Class template old_ptr</span></h2> 29<p>boost::contract::old_ptr — Old value pointer that requires 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: <<a class="link" href="../../reference.html#header.boost.contract.old_hpp" title="Header <boost/contract/old.hpp>">boost/contract/old.hpp</a>> 33 34</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> 35<span class="keyword">class</span> <a class="link" href="old_ptr.html" title="Class template old_ptr">old_ptr</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.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.html#boost.contract.old_ptrconstruct-copy-destruct">construct/copy/destruct</a></span> 41 <a class="link" href="old_ptr.html#idm46268584850864-bb"><span class="identifier">old_ptr</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 42 43 <span class="comment">// <a class="link" href="old_ptr.html#idm46268584865904-bb">public member functions</a></span> 44 <span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span> <a class="link" href="old_ptr.html#idm46268584865344-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> 45 <span class="identifier">T</span> <span class="keyword">const</span> <span class="special">*</span> <a class="link" href="old_ptr.html#idm46268584859760-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="keyword">explicit</span> <a class="link" href="old_ptr.html#idm46268584854176-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> 47<span class="special">}</span><span class="special">;</span></pre></div> 48<div class="refsect1"> 49<a name="idm45988677439920"></a><h2>Description</h2> 50<p>This pointer can be set to point 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_idm46268584781184.html" title="Function make_old">boost::contract::make_old</a></code> (that is why this class does not have public non-default constructors):</p> 51<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">u</span> <span class="special">{</span> 52<span class="keyword">public</span><span class="special">:</span> 53 <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> 54 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">old_ptr</span><span class="special"><</span><span class="identifier">old_type</span><span class="special">></span> <span class="identifier">old_var</span> <span class="special">=</span> <span class="comment">// For copyable `old_type`.</span> 55 <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> 56 <span class="special">...</span> 57 <span class="special">}</span> 58 59 <span class="special">...</span> 60<span class="special">}</span><span class="special">;</span> 61</pre> 62<p><span class="bold"><strong>See Also:</strong></span></p> 63<p> <a class="link" href="../../boost_contract/tutorial.html#boost_contract.tutorial.old_values" title="Old Values"> Old Values</a></p> 64<p> 65</p> 66<p> 67 68</p> 69<div class="refsect2"> 70<a name="idm45988677406800"></a><h3>Template Parameters</h3> 71<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> 72<pre class="literallayout"><span class="keyword">typename</span> T</pre> 73<p>Type of the pointed old value. This type must be copyable (i.e., <code class="computeroutput">boost::contract::is_old_value_copyable<T>::value</code> must be <code class="computeroutput">true</code>), otherwise this pointer will always be null and this library will generate a compile-time error when the pointer is dereferenced. </p> 74</li></ol></div> 75</div> 76<div class="refsect2"> 77<a name="idm45988677402016"></a><h3> 78<a name="boost.contract.old_ptrconstruct-copy-destruct"></a><code class="computeroutput">old_ptr</code> 79 public 80 construct/copy/destruct</h3> 81<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> 82<pre class="literallayout"><a name="idm46268584850864-bb"></a><span class="identifier">old_ptr</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>Construct this old value pointer as null. </li></ol></div> 83</div> 84<div class="refsect2"> 85<a name="idm45988677395888"></a><h3> 86<a name="idm46268584865904-bb"></a><code class="computeroutput">old_ptr</code> public member functions</h3> 87<div class="orderedlist"><ol class="orderedlist" type="1"> 88<li class="listitem"> 89<pre class="literallayout"><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span> <a name="idm46268584865344-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 and 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<T>::value</code> is <code class="computeroutput">false</code>).</p> 90<p> 91</p> 92<div class="variablelist"><table border="0" class="variablelist compact"> 93<colgroup> 94<col align="left" valign="top"> 95<col> 96</colgroup> 97<tbody><tr> 98<td><p><span class="term">Returns:</span></p></td> 99<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"> 100 Constant Correctness</a>). </p></td> 101</tr></tbody> 102</table></div> 103</li> 104<li class="listitem"> 105<pre class="literallayout"><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">*</span> <a name="idm46268584859760-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>Structure-dereference this old value pointer. <p>This will 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<T>::value</code> is <code class="computeroutput">false</code>).</p> 106<p> 107</p> 108<div class="variablelist"><table border="0" class="variablelist compact"> 109<colgroup> 110<col align="left" valign="top"> 111<col> 112</colgroup> 113<tbody><tr> 114<td><p><span class="term">Returns:</span></p></td> 115<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"> 116 Constant Correctness</a>). </p></td> 117</tr></tbody> 118</table></div> 119</li> 120<li class="listitem"> 121<pre class="literallayout"><span class="keyword">explicit</span> <a name="idm46268584854176-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> 122<p> 123</p> 124<div class="variablelist"><table border="0" class="variablelist compact"> 125<colgroup> 126<col align="left" valign="top"> 127<col> 128</colgroup> 129<tbody><tr> 130<td><p><span class="term">Returns:</span></p></td> 131<td><p>True if this pointer is not null, false otherwise. </p></td> 132</tr></tbody> 133</table></div> 134</li> 135</ol></div> 136</div> 137</div> 138</div> 139<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 140<td align="left"></td> 141<td align="right"><div class="copyright-footer">Copyright © 2008-2019 Lorenzo Caminiti<p> 142 Distributed under the Boost Software License, Version 1.0 (see accompanying 143 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>) 144 </p> 145</div></td> 146</tr></table> 147<hr> 148<div class="spirit-nav"> 149<a accesskey="p" href="old_pointer.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../reference.html#header.boost.contract.old_hpp"><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="old_ptr_if_copyable.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 150</div> 151</body> 152</html> 153
