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<a name="boost.xpressive.value"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Struct template value</span></h2>
<p>boost::xpressive::value — <code class="computeroutput">value<></code> is a lazy wrapper for a value that can be used in xpressive semantic actions. </p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<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="../../xpressive/reference.html#header.boost.xpressive.regex_actions_hpp" title="Header <boost/xpressive/regex_actions.hpp>">boost/xpressive/regex_actions.hpp</a>>
</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="value.html" title="Struct template value">value</a> <span class="special">:</span>
<span class="keyword">public</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">extends</span><span class="special"><</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">terminal</span><span class="special"><</span> <span class="identifier">T</span> <span class="special">></span><span class="special">::</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">value</span><span class="special"><</span> <span class="identifier">T</span> <span class="special">></span> <span class="special">></span>
<span class="special">{</span>
<span class="comment">// <a class="link" href="value.html#boost.xpressive.valueconstruct-copy-destruct">construct/copy/destruct</a></span>
<a class="link" href="value.html#idp352672720-bb"><span class="identifier">value</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">explicit</span> <a class="link" href="value.html#idp352673760-bb"><span class="identifier">value</span></a><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
<span class="comment">// <a class="link" href="value.html#idp352669184-bb">public member functions</a></span>
<span class="identifier">T</span> <span class="special">&</span> <a class="link" href="value.html#idp352669744-bb"><span class="identifier">get</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span> <a class="link" href="value.html#idp352671136-bb"><span class="identifier">get</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp531458112"></a><h2>Description</h2>
<p>
Below is an example that shows where <code class="computeroutput"><code class="computeroutput">value<></code></code> is useful.</p>
<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"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">pi</span><span class="special">)</span>
<span class="special">{</span>
<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>
<span class="comment">// Use val() to hold the shared_ptr by value:</span>
<span class="identifier">sregex</span> <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">>></span> <span class="char">'!'</span> <span class="special">)</span><span class="special">;</span>
<span class="comment">// OK, rex holds a reference count to the integer.</span>
<span class="keyword">return</span> <span class="identifier">rex</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p> In the above code, <code class="computeroutput">xpressive::val()</code> is a function that returns a <code class="computeroutput">value<></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>
<div class="refsect2">
<a name="idp531489168"></a><h3>Template Parameters</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> T</pre>
<p>The type of the value to store.</p>
</li></ol></div>
</div>
<div class="refsect2">
<a name="idp531492304"></a><h3>
<a name="boost.xpressive.valueconstruct-copy-destruct"></a><code class="computeroutput">value</code>
public
construct/copy/destruct</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><a name="idp352672720-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>
<li class="listitem">
<pre class="literallayout"><span class="keyword">explicit</span> <a name="idp352673760-bb"></a><span class="identifier">value</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span> t<span class="special">)</span><span class="special">;</span></pre>Store a copy of <code class="computeroutput">t</code>. <p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term"><code class="computeroutput">t</code></span></p></td>
<td><p>The initial value. </p></td>
</tr></tbody>
</table></div></td>
</tr></tbody>
</table></div>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="idp531509280"></a><h3>
<a name="idp352669184-bb"></a><code class="computeroutput">value</code> public member functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="identifier">T</span> <span class="special">&</span> <a name="idp352669744-bb"></a><span class="identifier">get</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>
<p>This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span> <a name="idp352671136-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>
</ol></div>
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<td align="right"><div class="copyright-footer">Copyright © 2007 Eric Niebler<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
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