doc/html/boost/xpressive/value.html

   1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
   2 <html>
   3 <head>
   4 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   5 <title>Struct template value</title>
   6 <link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css">
   7 <meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
   8 <link rel="home" href="../../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
   9 <link rel="up" href="../../xpressive/reference.html#header.boost.xpressive.regex_actions_hpp" title="Header &lt;boost/xpressive/regex_actions.hpp&gt;">
  10 <link rel="prev" href="function.html" title="Struct template function">
  11 <link rel="next" href="reference.html" title="Struct template reference">
  12 </head>
  13 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
  14 <table cellpadding="2" width="100%"><tr>
  15 <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td>
  16 <td align="center"><a href="../../../../index.html">Home</a></td>
  17 <td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td>
  18 <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
  19 <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
  20 <td align="center"><a href="../../../../more/index.htm">More</a></td>
  21 </tr></table>
  22 <hr>
  23 <div class="spirit-nav">
  24 <a accesskey="p" href="function.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../xpressive/reference.html#header.boost.xpressive.regex_actions_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="reference.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
  25 </div>
  26 <div class="refentry">
  27 <a name="boost.xpressive.value"></a><div class="titlepage"></div>
  28 <div class="refnamediv">
  29 <h2><span class="refentrytitle">Struct template value</span></h2>
  30 <p>boost::xpressive::value &#8212; <code class="computeroutput">value&lt;&gt;</code> is a lazy wrapper for a value that can be used in xpressive semantic actions. </p>
  31 </div>
  32 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  33 <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="../../xpressive/reference.html#header.boost.xpressive.regex_actions_hpp" title="Header &lt;boost/xpressive/regex_actions.hpp&gt;">boost/xpressive/regex_actions.hpp</a>&gt;
  34
  35 </span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> T<span class="special">&gt;</span>
  36 <span class="keyword">struct</span> <a class="link" href="value.html" title="Struct template value">value</a> <span class="special">:</span>
  37   <span class="keyword">public</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">extends</span><span class="special">&lt;</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">terminal</span><span class="special">&lt;</span> <span class="identifier">T</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">value</span><span class="special">&lt;</span> <span class="identifier">T</span> <span class="special">&gt;</span> <span class="special">&gt;</span>
  38 <span class="special">{</span>
  39   <span class="comment">// <a class="link" href="value.html#boost.xpressive.valueconstruct-copy-destruct">construct/copy/destruct</a></span>
  40   <a class="link" href="value.html#idp783837616-bb"><span class="identifier">value</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
  41   <span class="keyword">explicit</span> <a class="link" href="value.html#idp783838656-bb"><span class="identifier">value</span></a><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  42
  43   <span class="comment">// <a class="link" href="value.html#idp783834080-bb">public member functions</a></span>
  44   <span class="identifier">T</span> <span class="special">&amp;</span> <a class="link" href="value.html#idp783834640-bb"><span class="identifier">get</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
  45   <span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&amp;</span> <a class="link" href="value.html#idp783836032-bb"><span class="identifier">get</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  46 <span class="special">}</span><span class="special">;</span></pre></div>
  47 <div class="refsect1">
  48 <a name="idp626558928"></a><h2>Description</h2>
  49 <p>
  50 Below is an example that shows where <code class="computeroutput"><code class="computeroutput">value&lt;&gt;</code></code> is useful.</p>
  51 <pre class="programlisting"><span class="identifier">sregex</span> <span class="identifier">good_voodoo</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">pi</span><span class="special">)</span>
  52 <span class="special">{</span>
  53     <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">xpressive</span><span class="special">;</span>
  54     <span class="comment">// Use val() to hold the shared_ptr by value:</span>
  55     <a class="link" href="basic_regex.html" title="Struct template basic_regex">sregex</a> <span class="identifier">rex</span> <span class="special">=</span> <span class="special">+</span><span class="special">(</span> <span class="identifier">_d</span> <span class="special">[</span> <span class="special">++</span><span class="special">*</span><span class="identifier">val</span><span class="special">(</span><span class="identifier">pi</span><span class="special">)</span> <span class="special">]</span> <span class="special">&gt;&gt;</span> <span class="char">'!'</span> <span class="special">)</span><span class="special">;</span>
  56     <span class="comment">// OK, rex holds a reference count to the integer.</span>
  57     <span class="keyword">return</span> <span class="identifier">rex</span><span class="special">;</span>
  58 <span class="special">}</span>
  59 </pre>
  60 <p> In the above code, <code class="computeroutput">xpressive::val()</code> is a function that returns a <code class="computeroutput">value&lt;&gt;</code> object. Had <code class="computeroutput">val()</code> not been used here, the operation <code class="computeroutput">++*pi</code> would have been evaluated eagerly once, instead of lazily when the regex match happens. </p>
  61 <div class="refsect2">
  62 <a name="idp626590128"></a><h3>Template Parameters</h3>
  63 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
  64 <pre class="literallayout"><span class="keyword">typename</span> T</pre>
  65 <p>The type of the value to store.</p>
  66 </li></ol></div>
  67 </div>
  68 <div class="refsect2">
  69 <a name="idp626593264"></a><h3>
  70 <a name="boost.xpressive.valueconstruct-copy-destruct"></a><code class="computeroutput">value</code>
  71         public
  72        construct/copy/destruct</h3>
  73 <div class="orderedlist"><ol class="orderedlist" type="1">
  74 <li class="listitem">
  75 <pre class="literallayout"><a name="idp783837616-bb"></a><span class="identifier">value</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>Store a default-constructed <code class="computeroutput">T</code>. </li>
  76 <li class="listitem">
  77 <pre class="literallayout"><span class="keyword">explicit</span> <a name="idp783838656-bb"></a><span class="identifier">value</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&amp;</span> t<span class="special">)</span><span class="special">;</span></pre>Store a copy of <code class="computeroutput">t</code>. <p>
  78 </p>
  79 <div class="variablelist"><table border="0" class="variablelist compact">
  80 <colgroup>
  81 <col align="left" valign="top">
  82 <col>
  83 </colgroup>
  84 <tbody><tr>
  85 <td><p><span class="term">Parameters:</span></p></td>
  86 <td><div class="variablelist"><table border="0" class="variablelist compact">
  87 <colgroup>
  88 <col align="left" valign="top">
  89 <col>
  90 </colgroup>
  91 <tbody><tr>
  92 <td><p><span class="term"><code class="computeroutput">t</code></span></p></td>
  93 <td><p>The initial value. </p></td>
  94 </tr></tbody>
  95 </table></div></td>
  96 </tr></tbody>
  97 </table></div>
  98 </li>
  99 </ol></div>
 100 </div>
 101 <div class="refsect2">
 102 <a name="idp626610368"></a><h3>
 103 <a name="idp783834080-bb"></a><code class="computeroutput">value</code> public member functions</h3>
 104 <div class="orderedlist"><ol class="orderedlist" type="1">
 105 <li class="listitem">
 106 <pre class="literallayout"><span class="identifier">T</span> <span class="special">&amp;</span> <a name="idp783834640-bb"></a><span class="identifier">get</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>
 107 <p>This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. </p>
 108 </li>
 109 <li class="listitem">
 110 <pre class="literallayout"><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&amp;</span> <a name="idp783836032-bb"></a><span class="identifier">get</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>Fetch the stored value. </li>
 111 </ol></div>
 112 </div>
 113 </div>
 114 </div>
 115 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 116 <td align="left"></td>
 117 <td align="right"><div class="copyright-footer">Copyright &#169; 2007 Eric Niebler<p>
 118         Distributed under the Boost Software License, Version 1.0. (See accompanying
 119         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 120       </p>
 121 </div></td>
 122 </tr></table>
 123 <hr>
 124 <div class="spirit-nav">
 125 <a accesskey="p" href="function.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../xpressive/reference.html#header.boost.xpressive.regex_actions_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="reference.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
 126 </div>
 127 </body>
 128 </html>