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: Metafunction Class</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="./metafunction.html" class="navigation-link">Prev</a> <a href="./lambda-expression.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./metafunction.html" class="navigation-link">Back</a> <a href="./lambda-expression.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="./metafunction-class.html" class="navigation-link">Metafunction Class</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="metafunction-class"> 15<h1><a class="toc-backref" href="./metafunctions-concepts.html#id1513">Metafunction Class</a></h1> 16<div class="section" id="summary"> 17<h3>Summary</h3> 18<p>A <em>metafunction class</em> is a certain form of metafunction representation 19that enables higher-order metaprogramming. More precisely, it's a class 20with a publicly-accessible nested <a class="reference internal" href="./metafunction.html">Metafunction</a> called <tt class="literal"><span class="pre"><a href="./apply.html" class="identifier">apply</a></span></tt>. 21Correspondingly, a metafunction class invocation is defined as invocation 22of its nested <tt class="literal"><span class="pre"><a href="./apply.html" class="identifier">apply</a></span></tt> metafunction.</p> 23</div> 24<div class="section" id="id827"> 25<h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3> 26<p>In the following table and subsequent specifications, <tt class="literal"><span class="pre">f</span></tt> is a <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>.</p> 27<table border="1" class="docutils table"> 28<colgroup> 29<col width="36%" /> 30<col width="32%" /> 31<col width="32%" /> 32</colgroup> 33<thead valign="bottom"> 34<tr><th class="head">Expression</th> 35<th class="head">Type</th> 36<th class="head">Complexity</th> 37</tr> 38</thead> 39<tbody valign="top"> 40<tr><td><tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a>::type</span></tt></td> 41<td>Any type</td> 42<td>Unspecified.</td> 43</tr> 44<tr><td><tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a><>::type</span></tt></td> 45<td>Any type</td> 46<td>Unspecified.</td> 47</tr> 48<tr><td><tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a><a1,...an>::type</span></tt></td> 49<td>Any type</td> 50<td>Unspecified.</td> 51</tr> 52</tbody> 53</table> 54</div> 55<div class="section" id="id828"> 56<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 57<pre class="literal-block"> 58typedef f::<a href="./apply.html" class="identifier">apply</a>::type x; 59</pre> 60<table class="docutils field-list" frame="void" rules="none"> 61<col class="field-name" /> 62<col class="field-body" /> 63<tbody valign="top"> 64<tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is a nullary <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>; <tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a>::type</span></tt> is a <em>type-name</em>.</td> 65</tr> 66<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction class invocation.</td> 67</tr> 68</tbody> 69</table> 70<!-- ................................................................................... --> 71<pre class="literal-block"> 72typedef f::<a href="./apply.html" class="identifier">apply</a><>::type x; 73</pre> 74<table class="docutils field-list" frame="void" rules="none"> 75<col class="field-name" /> 76<col class="field-body" /> 77<tbody valign="top"> 78<tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is a nullary <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>; <tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a><>::type</span></tt> is a <em>type-name</em>.</td> 79</tr> 80<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction class invocation.</td> 81</tr> 82</tbody> 83</table> 84<!-- ................................................................................... --> 85<pre class="literal-block"> 86typedef f::<a href="./apply.html" class="identifier">apply</a><a1,<em>...</em>a<em>n</em>>::type x; 87</pre> 88<table class="docutils field-list" frame="void" rules="none"> 89<col class="field-name" /> 90<col class="field-body" /> 91<tbody valign="top"> 92<tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is an <em>n</em>-ary metafunction class; <tt class="literal"><span class="pre"><a href="./apply.html" class="identifier">apply</a></span></tt> is a <a class="reference internal" href="./metafunction.html">Metafunction</a>.</td> 93</tr> 94<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction class 95invocation with the actual arguments <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>.</td> 96</tr> 97</tbody> 98</table> 99</div> 100<div class="section" id="id829"> 101<h3><a class="subsection-title" href="#models" name="models">Models</a></h3> 102<ul class="simple"> 103<li><a class="reference internal" href="./always.html">always</a></li> 104<li><a class="reference internal" href="./arg.html">arg</a></li> 105<li><a class="reference internal" href="./quote.html">quote</a></li> 106<li><a class="reference internal" href="./numeric-cast.html">numeric_cast</a></li> 107<li><a class="reference internal" href="./unpack-args.html">unpack_args</a></li> 108</ul> 109</div> 110<div class="section" id="id830"> 111<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 112<p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./metafunction.html">Metafunction</a>, <a class="reference internal" href="./lambda-expression.html">Lambda Expression</a>, <a class="reference internal" href="./invocation.html">invocation</a>, <a class="reference internal" href="./apply-wrap.html">apply_wrap</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./quote.html">quote</a></p> 113<!-- Metafunctions/Concepts//Lambda Expression |30 --> 114</div> 115</div> 116 117<div class="footer-separator"></div> 118<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./metafunction.html" class="navigation-link">Prev</a> <a href="./lambda-expression.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./metafunction.html" class="navigation-link">Back</a> <a href="./lambda-expression.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> 119<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 120Distributed under the Boost Software License, Version 1.0. (See accompanying 121file 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> 122</html> 123