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12<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./macros.html" class="navigation-link">Macros</a> / <a href="./asserts.html" class="navigation-link">Asserts</a> / <a href="./assert.html" class="navigation-link">BOOST_MPL_ASSERT</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="assert">
15<h1><a class="toc-backref" href="./asserts.html#id511" name="assert">BOOST_MPL_ASSERT</a></h1>
16<div class="section" id="assert-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19#define <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>( pred ) \
20    <em>unspecified token sequence</em> \
21/**/
22</pre>
23</div>
24<div class="section" id="assert-description">
25<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
26<p>Generates a compilation error when the predicate <tt class="literal"><span class="pre">pred</span></tt> holds false.</p>
27</div>
28<div class="section" id="assert-header">
29<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
30<pre class="literal-block">
31#include &lt;<a href="../../../../boost/mpl/assert.hpp" class="header">boost/mpl/assert.hpp</a>&gt;
32</pre>
33</div>
34<div class="section" id="assert-parameters">
35<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
36<table border="1" class="table">
37<colgroup>
38<col width="19%" />
39<col width="43%" />
40<col width="38%" />
41</colgroup>
42<thead valign="bottom">
43<tr><th>Parameter</th>
44<th>Requirement</th>
45<th>Description</th>
46</tr>
47</thead>
48<tbody valign="top">
49<tr><td><tt class="literal"><span class="pre">pred</span></tt></td>
50<td>Boolean nullary <a class="reference" href="./metafunction.html">Metafunction</a></td>
51<td>A predicate to be asserted.</td>
52</tr>
53</tbody>
54</table>
55</div>
56<div class="section" id="assert-expression-semantics">
57<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
58<p>For any boolean nullary <a class="reference" href="./metafunction.html">Metafunction</a> <tt class="literal"><span class="pre">pred</span></tt>:</p>
59<pre class="literal-block">
60<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( pred ));
61</pre>
62<table class="field-list" frame="void" rules="none">
63<col class="field-name" />
64<col class="field-body" />
65<tbody valign="top">
66<tr class="field"><th class="field-name">Return type:</th><td class="field-body">None.</td>
67</tr>
68<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Generates a compilation error if <tt class="literal"><span class="pre">pred::type::value</span> <span class="pre">!=</span> <span class="pre">true</span></tt>, otherwise
69has no effect. Note that double parentheses are required even if no commas
70appear in the condition.</p>
71<p>When possible within the compiler's diagnostic capabilities,
72the error message will include the predicate's full type name, and have a
73general form of:</p>
74<pre class="last literal-block">
75<em>...</em> ************ pred::************ <em>...</em>
76</pre>
77</td>
78</tr>
79</tbody>
80</table>
81</div>
82<div class="section" id="assert-example">
83<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
84<pre class="literal-block">
85template&lt; typename T, typename U &gt; struct my
86{
87    // ...
88    <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; T,U &gt; ));
89};
90
91my&lt;void*,char*&gt; test;
92
93// In instantiation of `my&lt;void, char*&gt;':
94//   instantiated from here
95// conversion from `
96//   mpl_::failed************boost::is_same&lt;void, char*&gt;::************' to
97//   non-scalar type `mpl_::assert&lt;false&gt;' requested
98</pre>
99</div>
100<div class="section" id="assert-see-also">
101<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
102<p><a class="reference" href="./asserts.html">Asserts</a>, <a class="refentry reference" href="./assert-not.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_ASSERT_NOT</span></tt></a>, <a class="refentry reference" href="./assert-msg.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_ASSERT_MSG</span></tt></a>, <a class="refentry reference" href="./assert-relation.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_ASSERT_RELATION</span></tt></a></p>
103<!-- modtime: November 10, 2004 04:45:28 +0000 -->
104<!-- Macros/Asserts//BOOST_MPL_ASSERT_MSG -->
105</div>
106</div>
107
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