boost_mpl/doc/refmanual/assert-msg.html

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<div class="section" id="assert-msg">
<h1><a class="toc-backref" href="./asserts.html#id512" name="assert-msg">BOOST_MPL_ASSERT_MSG</a></h1>
<div class="section" id="asserts-assert-synopsis">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
#define <a href="./assert-msg.html" class="identifier">BOOST_MPL_ASSERT_MSG</a>( condition, message, types ) \
    <em>unspecified token sequence</em> \
/**/
</pre>
</div>
<div class="section" id="asserts-assert-description">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p>Generates a compilation error with an embedded custom message when the condition 
doesn't hold.</p>
</div>
<div class="section" id="asserts-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="asserts-assert-parameters">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
<table border="1" class="table">
<colgroup>
<col width="15%" />
<col width="36%" />
<col width="48%" />
</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">condition</span></tt></td>
<td>An integral constant expression</td>
<td>A condition to be asserted.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">message</span></tt></td>
<td>A legal identifier token</td>
<td>A custom message in a form of a legal C++
identifier token.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">types</span></tt></td>
<td>A legal function parameter list</td>
<td>A parenthized list of types to be displayed
in the error message.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="asserts-assert-expression-semantics">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For any integral constant expression <tt class="literal"><span class="pre">expr</span></tt>, legal C++ identifier <tt class="literal"><span class="pre">message</span></tt>, and 
arbitrary types <tt class="literal"><span class="pre">t1</span></tt>, <tt class="literal"><span class="pre">t2</span></tt>,... <tt class="literal"><span class="pre">tn</span></tt>:</p>
<pre class="literal-block">
<a href="./assert-msg.html" class="identifier">BOOST_MPL_ASSERT_MSG</a>( expr, message, (t1, t2,... tn) );
</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">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">t1</span></tt>, <tt class="literal"><span class="pre">t2</span></tt>,... <tt class="literal"><span class="pre">tn</span></tt> are non-<tt class="literal"><span class="pre">void</span></tt>.</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">expr::value</span> <span class="pre">!=</span> <span class="pre">true</span></tt>, otherwise
has no effect.</p>
<p>When possible within the compiler's diagnostic capabilities,
the error message will include the <tt class="literal"><span class="pre">message</span></tt> identifier and the parenthized 
list of <tt class="literal"><span class="pre">t1</span></tt>, <tt class="literal"><span class="pre">t2</span></tt>,... <tt class="literal"><span class="pre">tn</span></tt> types, and have a general form of:</p>
<pre class="last literal-block">
<em>...</em> ************( <em>...</em>::message )************)(t1, t2,... tn) <em>...</em>
</pre>
</td>
</tr>
</tbody>
</table>
<pre class="literal-block">
<a href="./assert-msg.html" class="identifier">BOOST_MPL_ASSERT_MSG</a>( expr, message, (types&lt;t1, t2,... tn&gt;) );
</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">Precondition:</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">expr::value</span> <span class="pre">!=</span> <span class="pre">true</span></tt>, otherwise
has no effect.</p>
<p>When possible within the compiler's diagnostics capabilities,
the error message will include the <tt class="literal"><span class="pre">message</span></tt> identifier and the list of 
<tt class="literal"><span class="pre">t1</span></tt>, <tt class="literal"><span class="pre">t2</span></tt>,... <tt class="literal"><span class="pre">tn</span></tt> types, and have a general form of:</p>
<pre class="last literal-block">
<em>...</em> ************( <em>...</em>::message )************)(types&lt;t1, t2,... tn&gt;) <em>...</em>
</pre>
</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="asserts-assert-example">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
template&lt; typename T &gt; struct my
{
    // ...
    <a href="./assert-msg.html" class="identifier">BOOST_MPL_ASSERT_MSG</a>( 
          is_integral&lt;T&gt;::value
        , NON_INTEGRAL_TYPES_ARE_NOT_ALLOWED
        , (T)
        );
};

my&lt;void*&gt; test;

// In instantiation of `my&lt;void*&gt;':
//   instantiated from here
// conversion from `
//   mpl_::failed************(my&lt;void*&gt;::
//   NON_INTEGRAL_TYPES_ARE_NOT_ALLOWED::************)(void*)
//   ' to non-scalar type `mpl_::assert&lt;false&gt;' requested
</pre>
</div>
<div class="section" id="asserts-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.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_ASSERT</span></tt></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-relation.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_ASSERT_RELATION</span></tt></a></p>
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