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<title>The MPL Reference Manual: BOOST_MPL_ASSERT</title>
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<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./asserts.html" class="navigation-link">Prev</a>&nbsp;<a href="./assert-msg.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group">Back&nbsp;<a href="./assert-msg.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./asserts.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>
<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>
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<div class="section" id="assert">
<h1><a class="toc-backref" href="./asserts.html#id511" name="assert">BOOST_MPL_ASSERT</a></h1>
<div class="section" id="assert-synopsis">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
#define <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>( pred ) \
<em>unspecified token sequence</em> \
/**/
</pre>
</div>
<div class="section" id="assert-description">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p>Generates a compilation error when the predicate <tt class="literal"><span class="pre">pred</span></tt> holds false.</p>
</div>
<div class="section" id="assert-header">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/assert.hpp" class="header">boost/mpl/assert.hpp</a>&gt;
</pre>
</div>
<div class="section" id="assert-parameters">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
<table border="1" class="table">
<colgroup>
<col width="19%" />
<col width="43%" />
<col width="38%" />
</colgroup>
<thead valign="bottom">
<tr><th>Parameter</th>
<th>Requirement</th>
<th>Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">pred</span></tt></td>
<td>Boolean nullary <a class="reference" href="./metafunction.html">Metafunction</a></td>
<td>A predicate to be asserted.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="assert-expression-semantics">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For any boolean nullary <a class="reference" href="./metafunction.html">Metafunction</a> <tt class="literal"><span class="pre">pred</span></tt>:</p>
<pre class="literal-block">
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( pred ));
</pre>
<table class="field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Return type:</th><td class="field-body">None.</td>
</tr>
<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
has no effect. Note that double parentheses are required even if no commas
appear in the condition.</p>
<p>When possible within the compiler's diagnostic capabilities,
the error message will include the predicate's full type name, and have a
general form of:</p>
<pre class="last literal-block">
<em>...</em> ************ pred::************ <em>...</em>
</pre>
</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="assert-example">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
template&lt; typename T, typename U &gt; struct my
{
// ...
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; T,U &gt; ));
};
my&lt;void*,char*&gt; test;
// In instantiation of `my&lt;void, char*&gt;':
// instantiated from here
// conversion from `
// mpl_::failed************boost::is_same&lt;void, char*&gt;::************' to
// non-scalar type `mpl_::assert&lt;false&gt;' requested
</pre>
</div>
<div class="section" id="assert-see-also">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<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>
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