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7<title>The MPL Reference Manual: has_key</title>
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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#id363" name="has-key">has_key</a></h1>
16<div class="section" id="has-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19template&lt;
20      typename Sequence
21    , typename Key
22    &gt;
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="has-description">
30<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
31<p>Returns a true-valued <a class="reference" 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="has-header">
35<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
36<pre class="literal-block">
37#include &lt;<a href="../../../../boost/mpl/has_key.hpp" class="header">boost/mpl/has_key.hpp</a>&gt;
38</pre>
39</div>
40<div class="section" id="has-model-of">
41<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3>
42<p><a class="reference" href="./tag-dispatched.html">Tag Dispatched Metafunction</a></p>
43</div>
44<div class="section" id="has-parameters">
45<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
46<table border="1" class="table">
47<colgroup>
48<col width="17%" />
49<col width="30%" />
50<col width="53%" />
51</colgroup>
52<thead valign="bottom">
53<tr><th>Parameter</th>
54<th>Requirement</th>
55<th>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" 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="has-expression-semantics">
71<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
72<p>For any <a class="reference" 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>&lt;s,key&gt;::type c;
75</pre>
76<table class="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" 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="has-complexity">
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="has-example">
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>&lt; <a href="./pair.html" class="identifier">pair</a>&lt;int,unsigned&gt;, <a href="./pair.html" class="identifier">pair</a>&lt;char,long&gt; &gt; m;
96<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( <a href="./has-key.html" class="identifier">has_key</a>&lt;m,long&gt; ));
97
98typedef <a href="./insert.html" class="identifier">insert</a>&lt; m, <a href="./pair.html" class="identifier">pair</a>&lt;long,unsigned long&gt; &gt; m1;
99<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./has-key.html" class="identifier">has_key</a>&lt;m1,long&gt; ));
100</pre>
101</div>
102<div class="section" id="has-see-also">
103<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
104<p><a class="reference" href="./associative-sequence.html">Associative Sequence</a>, <a class="refentry reference" href="./count.html"><tt class="refentry literal"><span class="pre">count</span></tt></a>, <a class="refentry reference" href="./insert.html"><tt class="refentry literal"><span class="pre">insert</span></tt></a>, <a class="refentry reference" href="./erase-key.html"><tt class="refentry literal"><span class="pre">erase_key</span></tt></a></p>
105<!-- modtime: November 13, 2004 01:28:31 +0000 -->
106<!-- Sequences/Intrinsic Metafunctions//insert -->
107</div>
108</div>
109
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