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10<title>The MPL Reference Manual: has_key</title>
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15<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>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="has-key">
18<h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id363" name="has-key">has_key</a></h1>
19<div class="section" id="has-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22template&lt;
23      typename Sequence
24    , typename Key
25    &gt;
26struct <a href="./has-key.html" class="identifier">has_key</a>
27{
28    typedef <em>unspecified</em> type;
29};
30</pre>
31</div>
32<div class="section" id="has-description">
33<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
34<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
35with key <tt class="literal"><span class="pre">Key</span></tt>.</p>
36</div>
37<div class="section" id="has-header">
38<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
39<pre class="literal-block">
40#include &lt;<a href="../../../../boost/mpl/has_key.hpp" class="header">boost/mpl/has_key.hpp</a>&gt;
41</pre>
42</div>
43<div class="section" id="has-model-of">
44<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3>
45<p><a class="reference" href="./tag-dispatched.html">Tag Dispatched Metafunction</a></p>
46</div>
47<div class="section" id="has-parameters">
48<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
49<table border="1" class="table">
50<colgroup>
51<col width="17%" />
52<col width="30%" />
53<col width="53%" />
54</colgroup>
55<thead valign="bottom">
56<tr><th>Parameter</th>
57<th>Requirement</th>
58<th>Description</th>
59</tr>
60</thead>
61<tbody valign="top">
62<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
63<td><a class="reference" href="./associative-sequence.html">Associative Sequence</a></td>
64<td>A sequence to query.</td>
65</tr>
66<tr><td><tt class="literal"><span class="pre">Key</span></tt></td>
67<td>Any type</td>
68<td>The queried key.</td>
69</tr>
70</tbody>
71</table>
72</div>
73<div class="section" id="has-expression-semantics">
74<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
75<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>
76<pre class="literal-block">
77typedef <a href="./has-key.html" class="identifier">has_key</a>&lt;s,key&gt;::type c;
78</pre>
79<table class="field-list" frame="void" rules="none">
80<col class="field-name" />
81<col class="field-body" />
82<tbody valign="top">
83<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>
84</tr>
85<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
86<tt class="literal"><span class="pre">c::value</span> <span class="pre">==</span> <span class="pre">false</span></tt>.</td>
87</tr>
88</tbody>
89</table>
90</div>
91<div class="section" id="has-complexity">
92<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
93<p>Amortized constant time.</p>
94</div>
95<div class="section" id="has-example">
96<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
97<pre class="literal-block">
98typedef <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;
99<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; ));
100
101typedef <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;
102<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./has-key.html" class="identifier">has_key</a>&lt;m1,long&gt; ));
103</pre>
104</div>
105<div class="section" id="has-see-also">
106<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
107<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>
108<!-- modtime: November 13, 2004 01:28:31 +0000 -->
109<!-- Sequences/Intrinsic Metafunctions//insert -->
110</div>
111</div>
112
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