<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>at_key</title> <link rel="stylesheet" href="../../../../../../../../doc/html/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.1"> <link rel="home" href="../../../../index.html" title="Chapter 1. Fusion 2.0"> <link rel="up" href="../functions.html" title="Functions"> <link rel="prev" href="has_key.html" title="has_key"> <link rel="next" href="swap.html" title="swap"> </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="../../../../../../../libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="has_key.html"><img src="../../../../../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.html"><img src="../../../../../../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="swap.html"><img src="../../../../../../../../doc/html/images/next.png" alt="Next"></a> </div> <div class="section" title="at_key"> <div class="titlepage"><div><div><h5 class="title"> <a name="fusion.sequence.intrinsic.functions.at_key"></a><a class="link" href="at_key.html" title="at_key">at_key</a> </h5></div></div></div> <a name="fusion.sequence.intrinsic.functions.at_key.description"></a><h6> <a name="id663530"></a> <a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.description">Description</a> </h6> <p> Returns the element associated with a Key from the sequence. </p> <a name="fusion.sequence.intrinsic.functions.at_key.synopsis"></a><h6> <a name="id663546"></a> <a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.synopsis">Synopsis</a> </h6> <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Key</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span> <span class="keyword">typename</span> <a class="link" href="../metafunctions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">,</span> <span class="identifier">Key</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">at_key</span><span class="special">(</span><span class="identifier">Sequence</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span> <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Key</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span> <span class="keyword">typename</span> <a class="link" href="../metafunctions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></a><span class="special"><</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">,</span> <span class="identifier">Key</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">at_key</span><span class="special">(</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span> </pre> <a name="fusion.sequence.intrinsic.functions.at_key.parameters"></a><h6> <a name="id663779"></a> <a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.parameters">Parameters</a> </h6> <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">seq</span></code> </p> </td> <td> <p> Model of <a class="link" href="../../concepts/associative_sequence.html" title="Associative Sequence">Associative Sequence</a> </p> </td> <td> <p> The sequence we wish to investigate. </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">Key</span></code> </p> </td> <td> <p> Any type </p> </td> <td> <p> The queried key. </p> </td> </tr> </tbody> </table></div> <a name="fusion.sequence.intrinsic.functions.at_key.expression_semantics"></a><h6> <a name="id663900"></a> <a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.expression_semantics">Expression Semantics</a> </h6> <pre class="programlisting"><span class="identifier">at_key</span><span class="special"><</span><span class="identifier">Key</span><span class="special">>(</span><span class="identifier">seq</span><span class="special">);</span> </pre> <p> <span class="bold"><strong>Return type</strong></span>: Returns a reference to the element associated with Key from the sequence <code class="computeroutput"><span class="identifier">seq</span></code> if <code class="computeroutput"><span class="identifier">seq</span></code> is mutable and <code class="computeroutput"><span class="identifier">e</span> <span class="special">=</span> <span class="identifier">o</span></code>, where <code class="computeroutput"><span class="identifier">e</span></code> is the element associated with Key, is a valid expression. Else, returns a type convertable to the element associated with Key. </p> <p> <span class="bold"><strong>Precondition</strong></span>: <code class="computeroutput"><span class="identifier">has_key</span><span class="special"><</span><span class="identifier">Key</span><span class="special">>(</span><span class="identifier">seq</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code> </p> <p> <span class="bold"><strong>Semantics</strong></span>: Returns the element associated with Key. </p> <a name="fusion.sequence.intrinsic.functions.at_key.header"></a><h6> <a name="id664041"></a> <a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.header">Header</a> </h6> <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">sequence</span><span class="special">/</span><span class="identifier">intrinsic</span><span class="special">/</span><span class="identifier">at_key</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">at_key</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> </pre> <a name="fusion.sequence.intrinsic.functions.at_key.example"></a><h6> <a name="id664156"></a> <a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.example">Example</a> </h6> <pre class="programlisting"><a class="link" href="../../../container/set.html" title="set"><code class="computeroutput"><span class="identifier">set</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">></span> <span class="identifier">s</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="char">'x'</span><span class="special">,</span> <span class="keyword">true</span><span class="special">);</span> <span class="identifier">assert</span><span class="special">(</span><span class="identifier">at_key</span><span class="special"><</span><span class="keyword">char</span><span class="special">>(</span><span class="identifier">s</span><span class="special">)</span> <span class="special">==</span> <span class="char">'x'</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="has_key.html"><img src="../../../../../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.html"><img src="../../../../../../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="swap.html"><img src="../../../../../../../../doc/html/images/next.png" alt="Next"></a> </div> </body> </html>