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7<title>The MPL Reference Manual: if_c</title>
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11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./if.html" class="navigation-link">Prev</a>&nbsp;<a href="./eval-if.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./if.html" class="navigation-link">Back</a>&nbsp;<a href="./eval-if.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./type-selection.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</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="./metafunctions.html" class="navigation-link">Metafunctions</a> / <a href="./type-selection.html" class="navigation-link">Type Selection</a> / <a href="./if-c.html" class="navigation-link">if_c</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="if-c">
15<h1><a class="toc-backref" href="./type-selection.html#id447" name="if-c">if_c</a></h1>
16<div class="section" id="type-if-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19template&lt; 
20      bool c
21    , typename T1
22    , typename T2
23    &gt;
24struct <a href="./if-c.html" class="identifier">if_c</a>
25{
26    typedef <em>unspecified</em> type;
27};
28</pre>
29</div>
30<div class="section" id="type-if-description">
31<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
32<p>Returns one of its two arguments, <tt class="literal"><span class="pre">T1</span></tt> or <tt class="literal"><span class="pre">T2</span></tt>, depending on the value of
33integral constant <tt class="literal"><span class="pre">c</span></tt>. <tt class="literal"><span class="pre"><a href="./if-c.html" class="identifier">if_c</a>&lt;c,t1,t2&gt;::type</span></tt> is a shorcut notation for
34<tt class="literal"><span class="pre"><a href="./if.html" class="identifier">if_</a>&lt;</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a>&lt;c&gt;,t1,t2</span> <span class="pre">&gt;::type</span></tt>.</p>
35</div>
36<div class="section" id="type-if-header">
37<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
38<pre class="literal-block">
39#include &lt;<a href="../../../../boost/mpl/if.hpp" class="header">boost/mpl/if.hpp</a>&gt;
40</pre>
41</div>
42<div class="section" id="type-if-parameters">
43<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
44<table border="1" class="table">
45<colgroup>
46<col width="15%" />
47<col width="36%" />
48<col width="48%" />
49</colgroup>
50<thead valign="bottom">
51<tr><th>Parameter</th>
52<th>Requirement</th>
53<th>Description</th>
54</tr>
55</thead>
56<tbody valign="top">
57<tr><td><tt class="literal"><span class="pre">c</span></tt></td>
58<td>An integral constant</td>
59<td>A selection condition.</td>
60</tr>
61<tr><td><tt class="literal"><span class="pre">T1</span></tt>, <tt class="literal"><span class="pre">T2</span></tt></td>
62<td>Any type</td>
63<td>Types to select from.</td>
64</tr>
65</tbody>
66</table>
67</div>
68<div class="section" id="type-if-expression-semantics">
69<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
70<p>For any integral constant <tt class="literal"><span class="pre">c</span></tt> and arbitrary types <tt class="literal"><span class="pre">t1</span></tt>, <tt class="literal"><span class="pre">t2</span></tt>:</p>
71<pre class="literal-block">
72typedef <a href="./if-c.html" class="identifier">if_c</a>&lt;c,t1,t2&gt;::type t;
73</pre>
74<table class="field-list" frame="void" rules="none">
75<col class="field-name" />
76<col class="field-body" />
77<tbody valign="top">
78<tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td>
79</tr>
80<tr class="field"><th class="field-name">Semantics:</th><td class="field-body">Equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre"><a href="./if.html" class="identifier">if_</a>&lt;</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a>&lt;c&gt;,t1,t2</span> <span class="pre">&gt;::type</span> <span class="pre">t;</span></tt></td>
81</tr>
82</tbody>
83</table>
84</div>
85<div class="section" id="type-if-example">
86<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
87<pre class="literal-block">
88typedef <a href="./if-c.html" class="identifier">if_c</a>&lt;true,char,long&gt;::type t1;
89typedef <a href="./if-c.html" class="identifier">if_c</a>&lt;false,char,long&gt;::type t2;
90
91<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;t1, char&gt; ));
92<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;t2, long&gt; ));
93</pre>
94</div>
95<div class="section" id="type-if-see-also">
96<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
97<p><a class="reference" href="./metafunctions.html">Metafunctions</a>, <a class="reference" href="./integral-constant.html">Integral Constant</a>, <a class="refentry reference" href="./if.html"><tt class="refentry literal"><span class="pre">if_</span></tt></a>, <a class="refentry reference" href="./eval-if.html"><tt class="refentry literal"><span class="pre">eval_if</span></tt></a>, <a class="refentry reference" href="./bool.html"><tt class="refentry literal"><span class="pre">bool_</span></tt></a></p>
98<!-- modtime: November 10, 2004 04:40:22 +0000 -->
99<!-- Metafunctions/Type Selection//eval_if |30 -->
100</div>
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102
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