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: lambda</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="./placeholders.html" class="navigation-link">Prev</a> <a href="./bind.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./placeholders.html" class="navigation-link">Back</a> <a href="./bind.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./composition-and-argument-binding.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="./composition-and-argument-binding.html" class="navigation-link">Composition and Argument Binding</a> / <a href="./lambda.html" class="navigation-link">lambda</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="lambda"> 15<h1><a class="toc-backref" href="./composition-and-argument-binding.html#id1530">lambda</a></h1> 16<div class="section" id="id922"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19template< 20 typename X 21 , typename Tag = <em>unspecified</em> 22 > 23struct <a href="./lambda.html" class="identifier">lambda</a> 24{ 25 typedef <em>unspecified</em> type; 26}; 27</pre> 28</div> 29<div class="section" id="id923"> 30<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 31<p>If <tt class="literal"><span class="pre">X</span></tt> is a <a class="reference internal" href="./placeholder-expression.html">Placeholder Expression</a>, transforms <tt class="literal"><span class="pre">X</span></tt> into a corresponding 32<a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>, otherwise <tt class="literal"><span class="pre">X</span></tt> is returned unchanged.</p> 33</div> 34<div class="section" id="id924"> 35<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 36<pre class="literal-block"> 37#include <<a href="../../../../boost/mpl/lambda.hpp" class="header">boost/mpl/lambda.hpp</a>> 38</pre> 39</div> 40<div class="section" id="id925"> 41<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> 42<table border="1" class="docutils table"> 43<colgroup> 44<col width="18%" /> 45<col width="27%" /> 46<col width="55%" /> 47</colgroup> 48<thead valign="bottom"> 49<tr><th class="head">Parameter</th> 50<th class="head">Requirement</th> 51<th class="head">Description</th> 52</tr> 53</thead> 54<tbody valign="top"> 55<tr><td><tt class="literal"><span class="pre">X</span></tt></td> 56<td>Any type</td> 57<td>An expression to transform.</td> 58</tr> 59<tr><td><tt class="literal"><span class="pre">Tag</span></tt></td> 60<td>Any type</td> 61<td>A tag determining transform semantics.</td> 62</tr> 63</tbody> 64</table> 65</div> 66<div class="section" id="id926"> 67<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 68<p>For arbitrary types <tt class="literal"><span class="pre">x</span></tt> and <tt class="literal"><span class="pre">tag</span></tt>:</p> 69<pre class="literal-block"> 70typedef <a href="./lambda.html" class="identifier">lambda</a><x>::type f; 71</pre> 72<table class="docutils field-list" frame="void" rules="none"> 73<col class="field-name" /> 74<col class="field-body" /> 75<tbody valign="top"> 76<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>.</p> 77</td> 78</tr> 79<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">If <tt class="literal"><span class="pre">x</span></tt> is a <a class="reference internal" href="./placeholder-expression.html">Placeholder Expression</a> in a general form <tt class="literal"><span class="pre">X<a1,...an></span></tt>, where 80<tt class="literal"><span class="pre">X</span></tt> is a class template and <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt> are arbitrary types, equivalent 81to</p> 82<pre class="literal-block"> 83typedef <a href="./protect.html" class="identifier">protect</a>< <a href="./bind.html" class="identifier">bind</a>< 84 <a href="./quote.html" class="identifier">quote</a><em>n</em><X> 85 , <a href="./lambda.html" class="identifier">lambda</a><a1>::type,<em>...</em> <a href="./lambda.html" class="identifier">lambda</a><a<em>n</em>>::type 86 > > f; 87</pre> 88<p class="last">otherwise, <tt class="literal"><span class="pre">f</span></tt> is identical to <tt class="literal"><span class="pre">x</span></tt>.</p> 89</td> 90</tr> 91</tbody> 92</table> 93<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ --> 94<pre class="literal-block"> 95typedef <a href="./lambda.html" class="identifier">lambda</a><x,tag>::type f; 96</pre> 97<table class="docutils field-list" frame="void" rules="none"> 98<col class="field-name" /> 99<col class="field-body" /> 100<tbody valign="top"> 101<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>.</p> 102</td> 103</tr> 104<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">If <tt class="literal"><span class="pre">x</span></tt> is a <a class="reference internal" href="./placeholder-expression.html">Placeholder Expression</a> in a general form <tt class="literal"><span class="pre">X<a1,...an></span></tt>, where 105<tt class="literal"><span class="pre">X</span></tt> is a class template and <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt> are arbitrary types, equivalent 106to</p> 107<pre class="literal-block"> 108typedef <a href="./protect.html" class="identifier">protect</a>< <a href="./bind.html" class="identifier">bind</a>< 109 <a href="./quote.html" class="identifier">quote</a><em>n</em><X,tag> 110 , <a href="./lambda.html" class="identifier">lambda</a><a1,tag>::type,<em>...</em> <a href="./lambda.html" class="identifier">lambda</a><a<em>n</em>,tag>::type 111 > > f; 112</pre> 113<p class="last">otherwise, <tt class="literal"><span class="pre">f</span></tt> is identical to <tt class="literal"><span class="pre">x</span></tt>.</p> 114</td> 115</tr> 116</tbody> 117</table> 118</div> 119<div class="section" id="id927"> 120<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 121<pre class="literal-block"> 122template< typename N1, typename N2 > struct int_plus 123 : <a href="./int.html" class="identifier">int_</a><( N1::value + N2::value )> 124{ 125}; 126 127typedef <a href="./lambda.html" class="identifier">lambda</a>< int_plus<<a href="./placeholders.html" class="identifier">_1</a>, <a href="./int.html" class="identifier">int_</a><42> > >::type f1; 128typedef <a href="./bind.html" class="identifier">bind</a>< <a href="./quote.html" class="identifier">quote</a><tt class="literal"><span class="pre">2</span></tt><int_plus>, <a href="./placeholders.html" class="identifier">_1</a>, <a href="./int.html" class="identifier">int_</a><42> > f2; 129 130typedef f1::<a href="./apply.html" class="identifier">apply</a><42>::type r1; 131typedef f2::<a href="./apply.html" class="identifier">apply</a><42>::type r2; 132 133<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( r1::value, ==, 84 ); 134<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( r2::value, ==, 84 ); 135</pre> 136</div> 137<div class="section" id="id928"> 138<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 139<p><a class="reference internal" href="./composition-and-argument-binding.html">Composition and Argument Binding</a>, <a class="reference internal" href="./invocation.html">invocation</a>, <a class="reference internal" href="./placeholders.html">Placeholders</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./quote.html">quote</a>, <a class="reference internal" href="./protect.html">protect</a>, <a class="reference internal" href="./apply.html">apply</a></p> 140<!-- Metafunctions/Composition and Argument Binding//bind |30 --> 141</div> 142</div> 143 144<div class="footer-separator"></div> 145<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./placeholders.html" class="navigation-link">Prev</a> <a href="./bind.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./placeholders.html" class="navigation-link">Back</a> <a href="./bind.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./composition-and-argument-binding.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> 146<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 147Distributed under the Boost Software License, Version 1.0. (See accompanying 148file 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> 149</html> 150