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- <title>The MPL Reference Manual: numeric_cast</title>
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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<
- typename SourceTag
- , typename TargetTag
- >
- 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 <<a href="../../../../boost/mpl/numeric_cast.hpp" class="header">boost/mpl/numeric_cast.hpp</a>>
- </pre>
- </div>
- <div class="section" id="id1184">
- <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
- <table border="1" class="docutils table">
- <colgroup>
- <col width="17%" />
- <col width="30%" />
- <col width="53%" />
- </colgroup>
- <thead valign="bottom">
- <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>< <a href="./numeric-cast.html" class="identifier">numeric_cast</a><x_tag,y_tag>,x >::type r;
- </pre>
- <table class="docutils 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">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><10> {};
- template< typename Re, typename Im > struct complex
- {
- typedef complex_tag tag;
- typedef complex type;
- typedef Re real;
- typedef Im imag;
- };
- template< typename C > struct real : C::real {};
- template< typename C > struct imag : C::imag {};
- namespace boost { namespace mpl {
- template<> struct <a href="./numeric-cast.html" class="identifier">numeric_cast</a>< integral_c_tag,complex_tag >
- {
- template< typename N > struct <a href="./apply.html" class="identifier">apply</a>
- : complex< N, <a href="./integral-c.html" class="identifier">integral_c</a>< typename N::<a href="./value-type.html" class="identifier">value_type</a>, 0 > >
- {
- };
- };
- template<>
- struct plus_impl< complex_tag,complex_tag >
- {
- template< typename N1, typename N2 > struct <a href="./apply.html" class="identifier">apply</a>
- : complex<
- <a href="./plus.html" class="identifier">plus</a>< typename N1::real, typename N2::real >
- , <a href="./plus.html" class="identifier">plus</a>< typename N1::imag, typename N2::imag >
- >
- {
- };
- };
- }}
- typedef <a href="./int.html" class="identifier">int_</a><2> i;
- typedef complex< <a href="./int.html" class="identifier">int_</a><5>, <a href="./int.html" class="identifier">int_</a><-1> > c1;
- typedef complex< <a href="./int.html" class="identifier">int_</a><-5>, <a href="./int.html" class="identifier">int_</a><1> > c2;
- typedef <a href="./plus.html" class="identifier">plus</a><c1,i> r4;
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real<r4>::value, ==, 7 );
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag<r4>::value, ==, -1 );
- typedef <a href="./plus.html" class="identifier">plus</a><i,c2> r5;
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real<r5>::value, ==, -3 );
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag<r5>::value, ==, 1 );
- </pre>
- </div>
- <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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