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12<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>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="numeric-cast">
15<h1><a class="toc-backref" href="./miscellaneous.html#id492" name="numeric-cast">numeric_cast</a></h1>
16<div class="section" id="numeric-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19template&lt; 
20      typename SourceTag
21    , typename TargetTag
22    &gt;
23struct <a href="./numeric-cast.html" class="identifier">numeric_cast</a>;
24</pre>
25</div>
26<div class="section" id="miscellaneous-numeric-description">
27<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
28<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" href="./metafunction-class.html">Metafunction Class</a> 
29providing a conversion between two numeric types.</p>
30</div>
31<div class="section" id="numeric-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/numeric_cast.hpp" class="header">boost/mpl/numeric_cast.hpp</a>&gt;
35</pre>
36</div>
37<div class="section" id="numeric-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="17%" />
42<col width="30%" />
43<col width="53%" />
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">SourceTag</span></tt></td>
53<td><a class="reference" href="./integral-constant.html">Integral Constant</a></td>
54<td>A tag for the conversion's source type.</td>
55</tr>
56<tr><td><tt class="literal"><span class="pre">TargetTag</span></tt></td>
57<td><a class="reference" href="./integral-constant.html">Integral Constant</a></td>
58<td>A tag for the conversion's destination type.</td>
59</tr>
60</tbody>
61</table>
62</div>
63<div class="section" id="miscellaneous-numeric-expression-semantics">
64<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
65<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
66<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" href="./integral-constant.html">Integral Constant</a> tags:</p>
67<pre class="literal-block">
68typedef <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;
69</pre>
70<table class="field-list" frame="void" rules="none">
71<col class="field-name" />
72<col class="field-body" />
73<tbody valign="top">
74<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
75</tr>
76<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>
77</tr>
78</tbody>
79</table>
80</div>
81<div class="section" id="numeric-complexity">
82<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
83<p>Unspecified.</p>
84</div>
85<div class="section" id="miscellaneous-numeric-example">
86<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
87<pre class="literal-block">
88struct complex_tag : <a href="./int.html" class="identifier">int_</a>&lt;10&gt; {};
89
90template&lt; typename Re, typename Im &gt; struct complex
91{
92    typedef complex_tag tag;
93    typedef complex type;
94    typedef Re real;
95    typedef Im imag;
96};
97
98template&lt; typename C &gt; struct real : C::real {};
99template&lt; typename C &gt; struct imag : C::imag {};
100
101namespace boost { namespace mpl {
102
103template&lt;&gt; struct <a href="./numeric-cast.html" class="identifier">numeric_cast</a>&lt; integral_c_tag,complex_tag &gt;
104{
105    template&lt; typename N &gt; struct <a href="./apply.html" class="identifier">apply</a>
106        : 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;
107    {
108    };
109};
110
111template&lt;&gt;
112struct plus_impl&lt; complex_tag,complex_tag &gt;
113{
114    template&lt; typename N1, typename N2 &gt; struct <a href="./apply.html" class="identifier">apply</a>
115        : complex&lt;
116              <a href="./plus.html" class="identifier">plus</a>&lt; typename N1::real, typename N2::real &gt;
117            , <a href="./plus.html" class="identifier">plus</a>&lt; typename N1::imag, typename N2::imag &gt;
118            &gt;
119    {
120    };
121};
122
123}}
124
125typedef <a href="./int.html" class="identifier">int_</a>&lt;2&gt; i;
126typedef 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;
127typedef 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;
128
129typedef <a href="./plus.html" class="identifier">plus</a>&lt;c1,i&gt; r4;
130<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real&lt;r4&gt;::value, ==, 7 );
131<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag&lt;r4&gt;::value, ==, -1 );
132
133typedef <a href="./plus.html" class="identifier">plus</a>&lt;i,c2&gt; r5;
134<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real&lt;r5&gt;::value, ==, -3 );
135<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag&lt;r5&gt;::value, ==, 1 );
136</pre>
137</div>
138<div class="section" id="miscellaneous-numeric-see-also">
139<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
140<p><a class="reference" href="./metafunctions.html">Metafunctions</a>, <a class="reference" href="./numeric-metafunction.html">Numeric Metafunction</a>, <a class="refentry reference" href="./plus.html"><tt class="refentry literal"><span class="pre">plus</span></tt></a>, <a class="refentry reference" href="./minus.html"><tt class="refentry literal"><span class="pre">minus</span></tt></a>, <a class="refentry reference" href="./times.html"><tt class="refentry literal"><span class="pre">times</span></tt></a></p>
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