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15<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>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="assert">
18<h1><a class="toc-backref" href="./asserts.html#id511" name="assert">BOOST_MPL_ASSERT</a></h1>
19<div class="section" id="assert-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22#define <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>( pred ) \
23    <em>unspecified token sequence</em> \
24/**/
25</pre>
26</div>
27<div class="section" id="assert-description">
28<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
29<p>Generates a compilation error when the predicate <tt class="literal"><span class="pre">pred</span></tt> holds false.</p>
30</div>
31<div class="section" id="assert-header">
32<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
33<pre class="literal-block">
34#include &lt;<a href="../../../../boost/mpl/assert.hpp" class="header">boost/mpl/assert.hpp</a>&gt;
35</pre>
36</div>
37<div class="section" id="assert-parameters">
38<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
39<table border="1" class="table">
40<colgroup>
41<col width="19%" />
42<col width="43%" />
43<col width="38%" />
44</colgroup>
45<thead valign="bottom">
46<tr><th>Parameter</th>
47<th>Requirement</th>
48<th>Description</th>
49</tr>
50</thead>
51<tbody valign="top">
52<tr><td><tt class="literal"><span class="pre">pred</span></tt></td>
53<td>Boolean nullary <a class="reference" href="./metafunction.html">Metafunction</a></td>
54<td>A predicate to be asserted.</td>
55</tr>
56</tbody>
57</table>
58</div>
59<div class="section" id="assert-expression-semantics">
60<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
61<p>For any boolean nullary <a class="reference" href="./metafunction.html">Metafunction</a> <tt class="literal"><span class="pre">pred</span></tt>:</p>
62<pre class="literal-block">
63<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( pred ));
64</pre>
65<table class="field-list" frame="void" rules="none">
66<col class="field-name" />
67<col class="field-body" />
68<tbody valign="top">
69<tr class="field"><th class="field-name">Return type:</th><td class="field-body">None.</td>
70</tr>
71<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
72has no effect. Note that double parentheses are required even if no commas
73appear in the condition.</p>
74<p>When possible within the compiler's diagnostic capabilities,
75the error message will include the predicate's full type name, and have a
76general form of:</p>
77<pre class="last literal-block">
78<em>...</em> ************ pred::************ <em>...</em>
79</pre>
80</td>
81</tr>
82</tbody>
83</table>
84</div>
85<div class="section" id="assert-example">
86<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
87<pre class="literal-block">
88template&lt; typename T, typename U &gt; struct my
89{
90    // ...
91    <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; T,U &gt; ));
92};
93
94my&lt;void*,char*&gt; test;
95
96// In instantiation of `my&lt;void, char*&gt;':
97//   instantiated from here
98// conversion from `
99//   mpl_::failed************boost::is_same&lt;void, char*&gt;::************' to
100//   non-scalar type `mpl_::assert&lt;false&gt;' requested
101</pre>
102</div>
103<div class="section" id="assert-see-also">
104<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
105<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>
106<!-- modtime: November 10, 2004 04:45:28 +0000 -->
107<!-- Macros/Asserts//BOOST_MPL_ASSERT_MSG -->
108</div>
109</div>
110
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