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<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="./miscellaneous.html" class="navigation-link">Miscellaneous</a> / <a href="./numeric-cast.html" class="navigation-link">numeric_cast</a></td>
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<div class="section" id="numeric-cast">
<h1><a class="toc-backref" href="./miscellaneous.html#id1568">numeric_cast</a></h1>
<div class="section" id="id1181">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
template&lt;
      typename SourceTag
    , typename TargetTag
    &gt;
struct <a href="./numeric-cast.html" class="identifier">numeric_cast</a>;
</pre>
</div>
<div class="section" id="id1182">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p>Each <tt class="literal"><span class="pre"><a href="./numeric-cast.html" class="identifier">numeric_cast</a></span></tt> specialization is a user-specialized unary <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>
providing a conversion between two numeric types.</p>
</div>
<div class="section" id="id1183">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/numeric_cast.hpp" class="header">boost/mpl/numeric_cast.hpp</a>&gt;
</pre>
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<div class="section" id="id1184">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<tr><th class="head">Parameter</th>
<th class="head">Requirement</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">SourceTag</span></tt></td>
<td><a class="reference internal" href="./integral-constant.html">Integral Constant</a></td>
<td>A tag for the conversion's source type.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">TargetTag</span></tt></td>
<td><a class="reference internal" href="./integral-constant.html">Integral Constant</a></td>
<td>A tag for the conversion's destination type.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id1185">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>If <tt class="literal"><span class="pre">x</span></tt> and <tt class="literal"><span class="pre">y</span></tt> are two numeric types, <tt class="literal"><span class="pre">x</span></tt> is convertible to <tt class="literal"><span class="pre">y</span></tt>, and
<tt class="literal"><span class="pre">x_tag</span></tt> and <tt class="literal"><span class="pre">y_tag</span></tt> are the types' corresponding <a class="reference internal" href="./integral-constant.html">Integral Constant</a> tags:</p>
<pre class="literal-block">
typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">2</span></tt>&lt; <a href="./numeric-cast.html" class="identifier">numeric_cast</a>&lt;x_tag,y_tag&gt;,x &gt;::type  r;
</pre>
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<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">r</span></tt> is a value of <tt class="literal"><span class="pre">x</span></tt> converted to the type of <tt class="literal"><span class="pre">y</span></tt>.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id1186">
<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
<p>Unspecified.</p>
</div>
<div class="section" id="id1187">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
struct complex_tag : <a href="./int.html" class="identifier">int_</a>&lt;10&gt; {};

template&lt; typename Re, typename Im &gt; struct complex
{
    typedef complex_tag tag;
    typedef complex type;
    typedef Re real;
    typedef Im imag;
};

template&lt; typename C &gt; struct real : C::real {};
template&lt; typename C &gt; struct imag : C::imag {};

namespace boost { namespace mpl {

template&lt;&gt; struct <a href="./numeric-cast.html" class="identifier">numeric_cast</a>&lt; integral_c_tag,complex_tag &gt;
{
    template&lt; typename N &gt; struct <a href="./apply.html" class="identifier">apply</a>
        : complex&lt; N, <a href="./integral-c.html" class="identifier">integral_c</a>&lt; typename N::<a href="./value-type.html" class="identifier">value_type</a>, 0 &gt; &gt;
    {
    };
};

template&lt;&gt;
struct plus_impl&lt; complex_tag,complex_tag &gt;
{
    template&lt; typename N1, typename N2 &gt; struct <a href="./apply.html" class="identifier">apply</a>
        : complex&lt;
              <a href="./plus.html" class="identifier">plus</a>&lt; typename N1::real, typename N2::real &gt;
            , <a href="./plus.html" class="identifier">plus</a>&lt; typename N1::imag, typename N2::imag &gt;
            &gt;
    {
    };
};

}}

typedef <a href="./int.html" class="identifier">int_</a>&lt;2&gt; i;
typedef complex&lt; <a href="./int.html" class="identifier">int_</a>&lt;5&gt;, <a href="./int.html" class="identifier">int_</a>&lt;-1&gt; &gt; c1;
typedef complex&lt; <a href="./int.html" class="identifier">int_</a>&lt;-5&gt;, <a href="./int.html" class="identifier">int_</a>&lt;1&gt; &gt; c2;

typedef <a href="./plus.html" class="identifier">plus</a>&lt;c1,i&gt; r4;
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real&lt;r4&gt;::value, ==, 7 );
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag&lt;r4&gt;::value, ==, -1 );

typedef <a href="./plus.html" class="identifier">plus</a>&lt;i,c2&gt; r5;
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real&lt;r5&gt;::value, ==, -3 );
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag&lt;r5&gt;::value, ==, 1 );
</pre>
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<div class="section" id="id1188">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./numeric-metafunction.html">Numeric Metafunction</a>, <a class="reference internal" href="./plus.html">plus</a>, <a class="reference internal" href="./minus.html">minus</a>, <a class="reference internal" href="./times.html">times</a></p>
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