<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>category_of</title> <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../../index.html" title="Chapter 1. Fusion 2.0"> <link rel="up" href="../support.html" title="Support"> <link rel="prev" href="tag_of.html" title="tag_of"> <link rel="next" href="deduce.html" title="deduce"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> <td align="center"><a href="../../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td 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href="category_of.html#fusion.support.category_of.description">Description</a> </h5> <p> A metafunction that establishes the conceptual classification of a particular <a class="link" href="../sequence.html" title="Sequence">Sequence</a> or <a class="link" href="../iterator.html" title="Iterator">Iterator</a> (see <a class="link" href="../iterator/concepts.html" title="Concepts">Iterator Concepts</a> and <a class="link" href="../sequence/concepts.html" title="Concepts">Sequence Concepts</a>). </p> <a name="fusion.support.category_of.synopsis"></a><h5> <a name="id879168"></a> <a class="link" href="category_of.html#fusion.support.category_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">T</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">category_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> <a name="fusion.support.category_of.parameters"></a><h5> <a name="id879261"></a> <a class="link" href="category_of.html#fusion.support.category_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> <a name="fusion.support.category_of.expression_semantics"></a><h5> <a name="id879349"></a> <a class="link" href="category_of.html#fusion.support.category_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">category_of</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">category</span><span class="special">;</span> </pre> <p> <span class="bold"><strong>Return type</strong></span>: </p> <p> The return type is derived from one of: </p> <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">fusion</span> <span class="special">{</span> <span class="keyword">struct</span> <span class="identifier">incrementable_traversal_tag</span> <span class="special">{};</span> <span class="keyword">struct</span> <span class="identifier">single_pass_traversal_tag</span> <span class="special">:</span> <span class="identifier">incrementable_traversal_tag</span> <span class="special">{};</span> <span class="keyword">struct</span> <span class="identifier">forward_traversal_tag</span> <span class="special">:</span> <span class="identifier">single_pass_traversal_tag</span> <span class="special">{};</span> <span class="keyword">struct</span> <span class="identifier">bidirectional_traversal_tag</span> <span class="special">:</span> <span class="identifier">forward_traversal_tag</span> <span class="special">{};</span> <span class="keyword">struct</span> <span class="identifier">random_access_traversal_tag</span> <span class="special">:</span> <span class="identifier">bidirectional_traversal_tag</span> <span class="special">{};</span> <span class="special">}}</span> </pre> <p> And optionally from: </p> <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">fusion</span> <span class="special">{</span> <span class="keyword">struct</span> <span class="identifier">associative_tag</span> <span class="special">{};</span> <span class="special">}}</span> </pre> <p> <span class="bold"><strong>Semantics</strong></span>: Establishes the conceptual classification of a particular <a class="link" href="../sequence.html" title="Sequence">Sequence</a> or <a class="link" href="../iterator.html" title="Iterator">Iterator</a>. </p> <a name="fusion.support.category_of.header"></a><h5> <a name="id879638"></a> <a class="link" href="category_of.html#fusion.support.category_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">category_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">category_of</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> </pre> <a name="fusion.support.category_of.example"></a><h5> <a name="id879746"></a> <a class="link" href="category_of.html#fusion.support.category_of.example">Example</a> </h5> <pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_base_of</span><span class="special">;</span> <span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">category_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">list_category</span><span class="special">;</span> <span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">category_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">vector_category</span><span class="special">;</span> <span class="identifier">BOOST_MPL_ASSERT</span><span class="special">((</span> <span class="identifier">is_base_of</span><span class="special"><</span><span class="identifier">forward_traversal_tag</span><span class="special">,</span> <span class="identifier">list_category</span><span class="special">></span> <span class="special">));</span> <span class="identifier">BOOST_MPL_ASSERT</span><span class="special">((</span> <span class="identifier">is_base_of</span><span class="special"><</span><span class="identifier">random_access_traversal_tag</span><span class="special">,</span> <span class="identifier">vector_category</span><span class="special">></span> <span class="special">));</span> </pre> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2001-2007 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>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="tag_of.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../support.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="deduce.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>