1<?xml version="1.0" encoding="utf-8" ?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4<head> 5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 6<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> 7<title>The MPL Reference Manual: Numeric Metafunction</title> 8<link rel="stylesheet" href="../style.css" type="text/css" /> 9</head> 10<body class="docframe refmanual"> 11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./tag-dispatched-metafunction.html" class="navigation-link">Prev</a> <a href="./trivial-metafunction.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./tag-dispatched-metafunction.html" class="navigation-link">Back</a> <a href="./trivial-metafunction.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 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="./metafunctions-concepts.html" class="navigation-link">Concepts</a> / <a href="./numeric-metafunction.html" class="navigation-link">Numeric Metafunction</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="numeric-metafunction"> 15<h1><a class="toc-backref" href="./metafunctions-concepts.html#id1517">Numeric Metafunction</a></h1> 16<div class="section" id="id847"> 17<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 18<p>A <a class="reference internal" href="./numeric-metafunction.html">Numeric Metafunction</a> is a <a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a> that provides 19a built-in infrastructure for easy implementation of mixed-type operations.</p> 20</div> 21<div class="section" id="id848"> 22<h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3> 23<p>In the following table and subsequent specifications, <tt class="literal"><span class="pre">op</span></tt> is a placeholder token for the actual 24<a class="reference internal" href="./numeric-metafunction.html">Numeric Metafunction</a>'s name, and <tt class="literal"><span class="pre">x</span></tt>, <tt class="literal"><span class="pre">y</span></tt> and <em>x</em><sub>1</sub>,<em>x</em><sub>2</sub>,... <em>x</em><sub>n</sub> are 25arbitrary numeric types.</p> 26<table border="1" class="docutils table"> 27<colgroup> 28<col width="46%" /> 29<col width="25%" /> 30<col width="29%" /> 31</colgroup> 32<thead valign="bottom"> 33<tr><th class="head">Expression</th> 34<th class="head">Type</th> 35<th class="head">Complexity</th> 36</tr> 37</thead> 38<tbody valign="top"> 39<tr><td><tt class="literal"><span class="pre">op_tag<x>::type</span></tt></td> 40<td><a class="reference internal" href="./integral-constant.html">Integral Constant</a></td> 41<td>Amortized constant time.</td> 42</tr> 43<tr><td><pre class="first last literal-block"> 44op_impl< 45 op_tag<x>::type 46 , op_tag<y>::type 47 >::<a href="./apply.html" class="identifier">apply</a><x,y>::type 48</pre> 49</td> 50<td>Any type</td> 51<td>Unspecified.</td> 52</tr> 53<tr><td><tt class="literal"><span class="pre">op<</span></tt><em>x</em><sub>1</sub>,<em>x</em><sub>2</sub>,... <em>x</em><sub>n</sub><tt class="literal"><span class="pre">>::type</span></tt></td> 54<td>Any type</td> 55<td>Unspecified.</td> 56</tr> 57</tbody> 58</table> 59</div> 60<div class="section" id="id849"> 61<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 62<pre class="literal-block"> 63typedef op_tag<x>::type tag; 64</pre> 65<table class="docutils field-list" frame="void" rules="none"> 66<col class="field-name" /> 67<col class="field-body" /> 68<tbody valign="top"> 69<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">tag</span></tt> is a tag type for <tt class="literal"><span class="pre">x</span></tt> for <tt class="literal"><span class="pre">op</span></tt>. 70<tt class="literal"><span class="pre">tag::value</span></tt> is <tt class="literal"><span class="pre">x</span></tt>'s <em>conversion rank</em>.</td> 71</tr> 72</tbody> 73</table> 74<!-- .......................................................................... --> 75<pre class="literal-block"> 76typedef op_impl< 77 op_tag<x>::type 78 , op_tag<y>::type 79 >::<a href="./apply.html" class="identifier">apply</a><x,y>::type r; 80</pre> 81<table class="docutils field-list" frame="void" rules="none"> 82<col class="field-name" /> 83<col class="field-body" /> 84<tbody valign="top"> 85<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">r</span></tt> is the result of <tt class="literal"><span class="pre">op</span></tt> application on arguments <tt class="literal"><span class="pre">x</span></tt> 86and <tt class="literal"><span class="pre">y</span></tt>.</td> 87</tr> 88</tbody> 89</table> 90<!-- .......................................................................... --> 91<pre class="literal-block"> 92typedef op<<em>x</em><sub>1</sub>,<em>x</em><sub>2</sub>,... <em>x</em><sub>n</sub>>::type r; 93</pre> 94<table class="docutils field-list" frame="void" rules="none"> 95<col class="field-name" /> 96<col class="field-body" /> 97<tbody valign="top"> 98<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">r</span></tt> is the result of <tt class="literal"><span class="pre">op</span></tt> application on arguments <em>x</em><sub>1</sub>,<em>x</em><sub>2</sub>,... <em>x</em><sub>n</sub>.</td> 99</tr> 100</tbody> 101</table> 102</div> 103<div class="section" id="id850"> 104<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 105<pre class="literal-block"> 106struct complex_tag : <a href="./int.html" class="identifier">int_</a><10> {}; 107 108template< typename Re, typename Im > struct complex 109{ 110 typedef complex_tag tag; 111 typedef complex type; 112 typedef Re real; 113 typedef Im imag; 114}; 115 116template< typename C > struct real : C::real {}; 117template< typename C > struct imag : C::imag {}; 118 119namespace boost { namespace mpl { 120 121template<> 122struct plus_impl< complex_tag,complex_tag > 123{ 124 template< typename N1, typename N2 > struct <a href="./apply.html" class="identifier">apply</a> 125 : complex< 126 <a href="./plus.html" class="identifier">plus</a>< typename N1::real, typename N2::real > 127 , <a href="./plus.html" class="identifier">plus</a>< typename N1::imag, typename N2::imag > 128 > 129 { 130 }; 131}; 132 133}} 134 135typedef complex< <a href="./int.html" class="identifier">int_</a><5>, <a href="./int.html" class="identifier">int_</a><-1> > c1; 136typedef complex< <a href="./int.html" class="identifier">int_</a><-5>, <a href="./int.html" class="identifier">int_</a><1> > c2; 137 138typedef <a href="./plus.html" class="identifier">plus</a><c1,c2> r1; 139<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real<r1>::value, ==, 0 ); 140<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag<r1>::value, ==, 0 ); 141 142typedef <a href="./plus.html" class="identifier">plus</a><c1,c1> r2; 143<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real<r2>::value, ==, 10 ); 144<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag<r2>::value, ==, -2 ); 145 146typedef <a href="./plus.html" class="identifier">plus</a><c2,c2> r3; 147<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( real<r3>::value, ==, -10 ); 148<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( imag<r3>::value, ==, 2 ); 149</pre> 150</div> 151<div class="section" id="id851"> 152<h3><a class="subsection-title" href="#models" name="models">Models</a></h3> 153<ul class="simple"> 154<li><a class="reference internal" href="./plus.html">plus</a></li> 155<li><a class="reference internal" href="./minus.html">minus</a></li> 156<li><a class="reference internal" href="./times.html">times</a></li> 157<li><a class="reference internal" href="./divides.html">divides</a></li> 158</ul> 159</div> 160<div class="section" id="id852"> 161<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 162<p><a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a>, <a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./numeric-cast.html">numeric_cast</a></p> 163<!-- Metafunctions/Concepts//Trivial Metafunction |70 --> 164</div> 165</div> 166 167<div class="footer-separator"></div> 168<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./tag-dispatched-metafunction.html" class="navigation-link">Prev</a> <a href="./trivial-metafunction.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./tag-dispatched-metafunction.html" class="navigation-link">Back</a> <a href="./trivial-metafunction.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 169<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 170Distributed under the Boost Software License, Version 1.0. (See accompanying 171file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> 172</html> 173