1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>at_key</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Chapter 1. Fusion 2.2"> 8<link rel="up" href="../functions.html" title="Functions"> 9<link rel="prev" href="has_key.html" title="has_key"> 10<link rel="next" href="swap.html" title="swap"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="has_key.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.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="swap.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<a name="fusion.sequence.intrinsic.functions.at_key"></a><a class="link" href="at_key.html" title="at_key">at_key</a> 28</h5></div></div></div> 29<h6> 30<a name="fusion.sequence.intrinsic.functions.at_key.h0"></a> 31 <span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.description"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.description">Description</a> 32 </h6> 33<p> 34 Returns the element associated with a Key from the sequence. 35 </p> 36<h6> 37<a name="fusion.sequence.intrinsic.functions.at_key.h1"></a> 38 <span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.synopsis"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.synopsis">Synopsis</a> 39 </h6> 40<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> 41<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> 42<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> 43 44<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> 45<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> 46<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> 47</pre> 48<h6> 49<a name="fusion.sequence.intrinsic.functions.at_key.h2"></a> 50 <span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.parameters"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.parameters">Parameters</a> 51 </h6> 52<div class="informaltable"><table class="table"> 53<colgroup> 54<col> 55<col> 56<col> 57</colgroup> 58<thead><tr> 59<th> 60 <p> 61 Parameter 62 </p> 63 </th> 64<th> 65 <p> 66 Requirement 67 </p> 68 </th> 69<th> 70 <p> 71 Description 72 </p> 73 </th> 74</tr></thead> 75<tbody> 76<tr> 77<td> 78 <p> 79 <code class="computeroutput"><span class="identifier">seq</span></code> 80 </p> 81 </td> 82<td> 83 <p> 84 Model of <a class="link" href="../../concepts/associative_sequence.html" title="Associative Sequence">Associative 85 Sequence</a> 86 </p> 87 </td> 88<td> 89 <p> 90 The sequence we wish to investigate. 91 </p> 92 </td> 93</tr> 94<tr> 95<td> 96 <p> 97 <code class="computeroutput"><span class="identifier">Key</span></code> 98 </p> 99 </td> 100<td> 101 <p> 102 Any type 103 </p> 104 </td> 105<td> 106 <p> 107 The queried key. 108 </p> 109 </td> 110</tr> 111</tbody> 112</table></div> 113<h6> 114<a name="fusion.sequence.intrinsic.functions.at_key.h3"></a> 115 <span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.expression_semantics"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.expression_semantics">Expression 116 Semantics</a> 117 </h6> 118<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> 119</pre> 120<p> 121 <span class="bold"><strong>Return type</strong></span>: Returns a reference to 122 the element associated with Key from the sequence <code class="computeroutput"><span class="identifier">seq</span></code> 123 if <code class="computeroutput"><span class="identifier">seq</span></code> is mutable and 124 <code class="computeroutput"><span class="identifier">e</span> <span class="special">=</span> 125 <span class="identifier">o</span></code>, where <code class="computeroutput"><span class="identifier">e</span></code> 126 is the element associated with Key, is a valid expression. Else, returns 127 a type convertible to the element associated with Key. 128 </p> 129<p> 130 <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> (where <code class="computeroutput"><span class="identifier">seq</span></code> 131 is not <a class="link" href="../../concepts/unbounded_sequence.html" title="Unbounded Sequence">Unbounded 132 Sequence</a>) 133 </p> 134<p> 135 <span class="bold"><strong>Semantics</strong></span>: Returns the element associated 136 with Key. 137 </p> 138<h6> 139<a name="fusion.sequence.intrinsic.functions.at_key.h4"></a> 140 <span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.header"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.header">Header</a> 141 </h6> 142<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> 143<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> 144</pre> 145<h6> 146<a name="fusion.sequence.intrinsic.functions.at_key.h5"></a> 147 <span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.example"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.example">Example</a> 148 </h6> 149<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> 150<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> 151</pre> 152</div> 153<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 154<td align="left"></td> 155<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman, 156 Dan Marsden, Tobias Schwinger<p> 157 Distributed under the Boost Software License, Version 1.0. (See accompanying 158 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>) 159 </p> 160</div></td> 161</tr></table> 162<hr> 163<div class="spirit-nav"> 164<a accesskey="p" href="has_key.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.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="swap.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 165</div> 166</body> 167</html> 168
