libs/core/doc/html/core/exchange.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>exchange</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.Core">
   8 <link rel="up" href="../index.html" title="Chapter&#160;1.&#160;Boost.Core">
   9 <link rel="prev" href="enable_if.html" title="enable_if">
  10 <link rel="next" href="explicit_operator_bool.html" title="explicit_operator_bool">
  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="enable_if.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="explicit_operator_bool.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="core.exchange"></a><a class="link" href="exchange.html" title="exchange">exchange</a>
  28 </h2></div></div></div>
  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="exchange.html#core.exchange.overview">Overview</a></span></dt>
  31 <dt><span class="section"><a href="exchange.html#core.exchange.examples">Examples</a></span></dt>
  32 <dt><span class="section"><a href="exchange.html#core.exchange.reference">Reference</a></span></dt>
  33 </dl></div>
  34 <div class="simplesect">
  35 <div class="titlepage"><div><div><h3 class="title">
  36 <a name="idm46687075842288"></a>Authors</h3></div></div></div>
  37 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
  38           Glen Fernandes
  39         </li></ul></div>
  40 </div>
  41 <div class="section">
  42 <div class="titlepage"><div><div><h3 class="title">
  43 <a name="core.exchange.overview"></a><a class="link" href="exchange.html#core.exchange.overview" title="Overview">Overview</a>
  44 </h3></div></div></div>
  45 <p>
  46         The header &lt;boost/core/exchange.hpp&gt; provides the function template
  47         <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">exchange</span></code> which is an implementation of
  48         the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exchange</span></code> function introduced in C++14.
  49         <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">exchange</span><span class="special">(</span><span class="identifier">o</span><span class="special">,</span> <span class="identifier">v</span><span class="special">)</span></code> replaces the value of <code class="computeroutput"><span class="identifier">o</span></code>
  50         with <code class="computeroutput"><span class="identifier">v</span></code> and returns the old
  51         value of <code class="computeroutput"><span class="identifier">o</span></code>.
  52       </p>
  53 </div>
  54 <div class="section">
  55 <div class="titlepage"><div><div><h3 class="title">
  56 <a name="core.exchange.examples"></a><a class="link" href="exchange.html#core.exchange.examples" title="Examples">Examples</a>
  57 </h3></div></div></div>
  58 <p>
  59         The following example shows <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">exchange</span></code>
  60         used to simplify the implementation of a move constructor.
  61       </p>
  62 <pre class="programlisting"><span class="identifier">Node</span><span class="special">(</span><span class="identifier">Node</span><span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span>
  63   <span class="special">:</span> <span class="identifier">head_</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">exchange</span><span class="special">(</span><span class="identifier">other</span><span class="special">.</span><span class="identifier">head_</span><span class="special">,</span> <span class="keyword">nullptr</span><span class="special">))</span>
  64   <span class="special">,</span> <span class="identifier">tail_</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">exchange</span><span class="special">(</span><span class="identifier">other</span><span class="special">.</span><span class="identifier">tail_</span><span class="special">,</span> <span class="keyword">nullptr</span><span class="special">))</span> <span class="special">{</span> <span class="special">}</span>
  65 </pre>
  66 </div>
  67 <div class="section">
  68 <div class="titlepage"><div><div><h3 class="title">
  69 <a name="core.exchange.reference"></a><a class="link" href="exchange.html#core.exchange.reference" title="Reference">Reference</a>
  70 </h3></div></div></div>
  71 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
  72   <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">U</span> <span class="special">=</span> <span class="identifier">T</span><span class="special">&gt;</span>
  73   <span class="keyword">constexpr</span> <span class="identifier">T</span> <span class="identifier">exchange</span><span class="special">(</span><span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">t</span><span class="special">,</span> <span class="identifier">U</span><span class="special">&amp;&amp;</span> <span class="identifier">u</span><span class="special">);</span>
  74 <span class="special">}</span>
  75 </pre>
  76 <div class="section">
  77 <div class="titlepage"><div><div><h4 class="title">
  78 <a name="core.exchange.reference.functions"></a><a class="link" href="exchange.html#core.exchange.reference.functions" title="Functions">Functions</a>
  79 </h4></div></div></div>
  80 <p>
  81           <span class="bold"><strong><code class="computeroutput"><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>
  82           <span class="identifier">U</span> <span class="special">=</span>
  83           <span class="identifier">T</span><span class="special">&gt;</span>
  84           <span class="keyword">constexpr</span> <span class="identifier">T</span>
  85           <span class="identifier">exchange</span><span class="special">(</span><span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">t</span><span class="special">,</span> <span class="identifier">U</span><span class="special">&amp;&amp;</span> <span class="identifier">u</span><span class="special">);</span></code></strong></span>
  86         </p>
  87 <p>
  88           Equivalent to:
  89         </p>
  90 <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">t</span><span class="special">);</span>
  91 <span class="identifier">t</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;(</span><span class="identifier">u</span><span class="special">);</span>
  92 <span class="keyword">return</span> <span class="identifier">v</span><span class="special">;</span>
  93 </pre>
  94 </div>
  95 </div>
  96 </div>
  97 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
  98 <td align="left"></td>
  99 <td align="right"><div class="copyright-footer">Copyright &#169; 2014 Peter Dimov<br>Copyright &#169; 2014 Glen Fernandes<br>Copyright &#169; 2014 Andrey Semashev<p>
 100         Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost
 101         Software License, Version 1.0</a>.
 102       </p>
 103 </div></td>
 104 </tr></table>
 105 <hr>
 106 <div class="spirit-nav">
 107 <a accesskey="p" href="enable_if.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="explicit_operator_bool.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
 108 </div>
 109 </body>
 110 </html>