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<html>
<head>
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<title>tag_of</title>
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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="fusion.support.tag_of"></a><a class="link" href="tag_of.html" title="tag_of">tag_of</a>
</h3></div></div></div>
<h5>
<a name="fusion.support.tag_of.h0"></a>
<span><a name="fusion.support.tag_of.description"></a></span><a class="link" href="tag_of.html#fusion.support.tag_of.description">Description</a>
</h5>
<p>
All conforming Fusion sequences and iterators have an associated tag type.
The purpose of the tag is to enable <a class="link" href="../notes.html#fusion.notes.tag_dispatching"><span class="emphasis"><em>tag
dispatching</em></span></a> from <a class="link" href="../sequence/intrinsic.html" title="Intrinsic">Intrinsic</a>
functions to implementations appropriate for the type.
</p>
<p>
This metafunction may be specialized to accomodate clients providing Fusion
conforming sequences.
</p>
<h5>
<a name="fusion.support.tag_of.h1"></a>
<span><a name="fusion.support.tag_of.synopsis"></a></span><a class="link" href="tag_of.html#fusion.support.tag_of.synopsis">Synopsis</a>
</h5>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">traits</span>
<span class="special">{</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">tag_of</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span> <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>
<span class="special">}</span>
</pre>
<h5>
<a name="fusion.support.tag_of.h2"></a>
<span><a name="fusion.support.tag_of.parameters"></a></span><a class="link" href="tag_of.html#fusion.support.tag_of.parameters">Parameters</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Requirement
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">T</span></code>
</p>
</td>
<td>
<p>
Any type
</p>
</td>
<td>
<p>
The type to query.
</p>
</td>
</tr></tbody>
</table></div>
<h5>
<a name="fusion.support.tag_of.h3"></a>
<span><a name="fusion.support.tag_of.expression_semantics"></a></span><a class="link" href="tag_of.html#fusion.support.tag_of.expression_semantics">Expression
Semantics</a>
</h5>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">tag_of</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">tag</span><span class="special">;</span>
</pre>
<p>
<span class="bold"><strong>Return type</strong></span>: Any type.
</p>
<p>
<span class="bold"><strong>Semantics</strong></span>: Returns the tag type associated
with <code class="computeroutput"><span class="identifier">T</span></code>.
</p>
<h5>
<a name="fusion.support.tag_of.h4"></a>
<span><a name="fusion.support.tag_of.header"></a></span><a class="link" href="tag_of.html#fusion.support.tag_of.header">Header</a>
</h5>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">support</span><span class="special">/</span><span class="identifier">tag_of</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">tag_of</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<h5>
<a name="fusion.support.tag_of.h5"></a>
<span><a name="fusion.support.tag_of.example"></a></span><a class="link" href="tag_of.html#fusion.support.tag_of.example">Example</a>
</h5>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">tag_of</span><span class="special"><</span><a class="link" href="../container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a><span class="special"><></span> <span class="special">>::</span><span class="identifier">type</span> <span class="identifier">tag1</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">tag_of</span><span class="special"><</span><a class="link" href="../container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">>::</span><span class="identifier">type</span> <span class="identifier">tag2</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">tag_of</span><span class="special"><</span><a class="link" href="../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><></span> <span class="special">>::</span><span class="identifier">type</span> <span class="identifier">tag3</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">tag_of</span><span class="special"><</span><a class="link" href="../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">>::</span><span class="identifier">type</span> <span class="identifier">tag4</span><span class="special">;</span>
<span class="identifier">BOOST_MPL_ASSERT</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">tag1</span><span class="special">,</span> <span class="identifier">tag2</span><span class="special">>));</span>
<span class="identifier">BOOST_MPL_ASSERT</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">tag3</span><span class="special">,</span> <span class="identifier">tag4</span><span class="special">>));</span>
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman,
Dan Marsden, Tobias Schwinger<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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