1<?xml version="1.0" encoding="utf-8" ?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4<head> 5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 6<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> 7<title>The MPL Reference Manual: has_key</title> 8<link rel="stylesheet" href="../style.css" type="text/css" /> 9</head> 10<body class="docframe refmanual"> 11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./front.html" class="navigation-link">Prev</a> <a href="./insert.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./front.html" class="navigation-link">Back</a> <a href="./insert.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./intrinsic-metafunctions.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 12<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./sequences.html" class="navigation-link">Sequences</a> / <a href="./intrinsic-metafunctions.html" class="navigation-link">Intrinsic Metafunctions</a> / <a href="./has-key.html" class="navigation-link">has_key</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="has-key"> 15<h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1435">has_key</a></h1> 16<div class="section" id="id265"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19template< 20 typename Sequence 21 , typename Key 22 > 23struct <a href="./has-key.html" class="identifier">has_key</a> 24{ 25 typedef <em>unspecified</em> type; 26}; 27</pre> 28</div> 29<div class="section" id="id266"> 30<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 31<p>Returns a true-valued <a class="reference internal" href="./integral-constant.html">Integral Constant</a> if <tt class="literal"><span class="pre">Sequence</span></tt> contains an element 32with key <tt class="literal"><span class="pre">Key</span></tt>.</p> 33</div> 34<div class="section" id="id267"> 35<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 36<pre class="literal-block"> 37#include <<a href="../../../../boost/mpl/has_key.hpp" class="header">boost/mpl/has_key.hpp</a>> 38</pre> 39</div> 40<div class="section" id="id268"> 41<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3> 42<p><a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a></p> 43</div> 44<div class="section" id="id269"> 45<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> 46<table border="1" class="docutils table"> 47<colgroup> 48<col width="17%" /> 49<col width="30%" /> 50<col width="53%" /> 51</colgroup> 52<thead valign="bottom"> 53<tr><th class="head">Parameter</th> 54<th class="head">Requirement</th> 55<th class="head">Description</th> 56</tr> 57</thead> 58<tbody valign="top"> 59<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td> 60<td><a class="reference internal" href="./associative-sequence.html">Associative Sequence</a></td> 61<td>A sequence to query.</td> 62</tr> 63<tr><td><tt class="literal"><span class="pre">Key</span></tt></td> 64<td>Any type</td> 65<td>The queried key.</td> 66</tr> 67</tbody> 68</table> 69</div> 70<div class="section" id="id270"> 71<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 72<p>For any <a class="reference internal" href="./associative-sequence.html">Associative Sequence</a> <tt class="literal"><span class="pre">s</span></tt>, and arbitrary type <tt class="literal"><span class="pre">key</span></tt>:</p> 73<pre class="literal-block"> 74typedef <a href="./has-key.html" class="identifier">has_key</a><s,key>::type c; 75</pre> 76<table class="docutils field-list" frame="void" rules="none"> 77<col class="field-name" /> 78<col class="field-body" /> 79<tbody valign="top"> 80<tr class="field"><th class="field-name">Return type:</th><td class="field-body">Boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</td> 81</tr> 82<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">c::value</span> <span class="pre">==</span> <span class="pre">true</span></tt> if <tt class="literal"><span class="pre">key</span></tt> is in <tt class="literal"><span class="pre">s</span></tt>'s set of keys; otherwise 83<tt class="literal"><span class="pre">c::value</span> <span class="pre">==</span> <span class="pre">false</span></tt>.</td> 84</tr> 85</tbody> 86</table> 87</div> 88<div class="section" id="id271"> 89<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3> 90<p>Amortized constant time.</p> 91</div> 92<div class="section" id="id272"> 93<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 94<pre class="literal-block"> 95typedef <a href="./map.html" class="identifier">map</a>< <a href="./pair.html" class="identifier">pair</a><int,unsigned>, <a href="./pair.html" class="identifier">pair</a><char,long> > m; 96<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( <a href="./has-key.html" class="identifier">has_key</a><m,long> )); 97 98typedef <a href="./insert.html" class="identifier">insert</a>< m, <a href="./pair.html" class="identifier">pair</a><long,unsigned long> > m1; 99<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./has-key.html" class="identifier">has_key</a><m1,long> )); 100</pre> 101</div> 102<div class="section" id="id273"> 103<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 104<p><a class="reference internal" href="./associative-sequence.html">Associative Sequence</a>, <a class="reference internal" href="./count.html">count</a>, <a class="reference internal" href="./insert.html">insert</a>, <a class="reference internal" href="./erase-key.html">erase_key</a></p> 105<!-- Sequences/Intrinsic Metafunctions//insert --> 106</div> 107</div> 108 109<div class="footer-separator"></div> 110<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./front.html" class="navigation-link">Prev</a> <a href="./insert.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./front.html" class="navigation-link">Back</a> <a href="./insert.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./intrinsic-metafunctions.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 111<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 112Distributed under the Boost Software License, Version 1.0. (See accompanying 113file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> 114</html> 115