libs/contract/doc/html/BOOST_CO_idm45394998674080.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>Macro BOOST_CONTRACT_OLD_PTR_IF_COPYABLE</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&#160;1.&#160;Boost.Contract 1.0.0">
   8 <link rel="up" href="reference.html#header.boost.contract_macro_hpp" title="Header &lt;boost/contract_macro.hpp&gt;">
   9 <link rel="prev" href="BOOST_CONTRACT_OLD_PTR.html" title="Macro BOOST_CONTRACT_OLD_PTR">
  10 <link rel="next" href="BOOST_CONTRACT_INVARIANT.html" title="Macro BOOST_CONTRACT_INVARIANT">
  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="BOOST_CONTRACT_OLD_PTR.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="reference.html#header.boost.contract_macro_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="BOOST_CONTRACT_INVARIANT.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="refentry">
  26 <a name="BOOST_CO_idm45394998674080"></a><div class="titlepage"></div>
  27 <div class="refnamediv">
  28 <h2><span class="refentrytitle">Macro BOOST_CONTRACT_OLD_PTR_IF_COPYABLE</span></h2>
  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 </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_macro_hpp" title="Header &lt;boost/contract_macro.hpp&gt;">boost/contract_macro.hpp</a>&gt;
  33
  34 </span>BOOST_CONTRACT_OLD_PTR_IF_COPYABLE(...)</pre></div>
  35 <div class="refsect1">
  36 <a name="idm45707992820784"></a><h2>Description</h2>
  37 <p>This is used to program old value copies for types that might or might not be copyable:</p>
  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 <span class="keyword">class</span> <span class="identifier">u</span> <span class="special">{</span>
  40 <span class="keyword">public</span><span class="special">:</span>
  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         <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         <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                 <span class="identifier">old_expr_b</span><span class="special">)</span><span class="special">;</span>
  45         <span class="identifier">BOOST_CONTRACT_PUBLIC_FUNCTION</span><span class="special">(</span><span class="keyword">this</span><span class="special">)</span>
  46             <span class="special">...</span>
  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                 <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                 <span class="special">...</span>
  50             <span class="special">}</span><span class="special">)</span>
  51             <span class="special">...</span> <span class="comment">// In postconditions or exception guarantees:</span>
  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                 <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             <span class="special">...</span>
  55         <span class="special">;</span>
  56
  57         <span class="special">...</span> <span class="comment">// Function body.</span>
  58     <span class="special">}</span>
  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         <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         <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                 <span class="identifier">old_expr_b</span><span class="special">)</span><span class="special">;</span>
  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             <span class="special">...</span>
  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                 <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                 <span class="special">...</span>
  69             <span class="special">}</span><span class="special">)</span>
  70             <span class="special">...</span> <span class="comment">// In postconditions or exception guarantees:</span>
  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                 <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             <span class="special">...</span>
  74         <span class="special">;</span>
  75
  76         <span class="special">...</span> <span class="comment">// Function body.</span>
  77     <span class="special">}</span>
  78
  79     <span class="special">...</span>
  80 <span class="special">}</span><span class="special">;</span>
  81 </pre>
  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 <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 <pre class="programlisting"><span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_CONTRACT_NO_OLDS</span>
  85     <span class="comment">// This declaration does not need to use `v`.</span>
  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 <span class="preprocessor">#endif</span>
  88 </pre>
  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 <pre class="programlisting"><span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_CONTRACT_NO_OLDS</span>
  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             <span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">old_expr</span><span class="special">)</span>
  93 <span class="preprocessor">#endif</span>
  94 </pre>
  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 <pre class="programlisting"><span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_CONTRACT_NO_OLDS</span>
  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             <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 <span class="preprocessor">#endif</span>
 100 </pre>
 101 <p>Where:</p>
 102 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 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 <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 <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 <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 </ul></div>
 108 <p>
 109 </p>
 110 <p><span class="bold"><strong>See Also:</strong></span></p>
 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         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         Old Value Requirements</a> </p>
 114 <p>
 115 </p>
 116 <p>
 117 </p>
 118 </div>
 119 </div>
 120 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 121 <td align="left"></td>
 122 <td align="right"><div class="copyright-footer">Copyright &#169; 2008-2019 Lorenzo Caminiti<p>
 123         Distributed under the Boost Software License, Version 1.0 (see accompanying
 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       </p>
 126 </div></td>
 127 </tr></table>
 128 <hr>
 129 <div class="spirit-nav">
 130 <a accesskey="p" href="BOOST_CONTRACT_OLD_PTR.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="reference.html#header.boost.contract_macro_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="BOOST_CONTRACT_INVARIANT.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
 131 </div>
 132 </body>
 133 </html>