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6<meta name="generator" content="Docutils 0.3.6: http://docutils.sourceforge.net/" />
7<title>The MPL Reference Manual: lambda</title>
8<link rel="stylesheet" href="../style.css" type="text/css" />
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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>&nbsp;<a href="./bind.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./placeholders.html" class="navigation-link">Back</a>&nbsp;<a href="./bind.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./composition-and-argument.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</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.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.html#id456" name="lambda">lambda</a></h1>
16<div class="section" id="lambda-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19template&lt; 
20      typename X
21    , typename Tag = <em>unspecified</em>
22    &gt;
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="composition-lambda-description">
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" href="./placeholder-expression.html">Placeholder Expression</a>, transforms <tt class="literal"><span class="pre">X</span></tt> into a corresponding
32<a class="reference" 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="lambda-header">
35<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
36<pre class="literal-block">
37#include &lt;<a href="../../../../boost/mpl/lambda.hpp" class="header">boost/mpl/lambda.hpp</a>&gt;
38</pre>
39</div>
40<div class="section" id="lambda-parameters">
41<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
42<table border="1" class="table">
43<colgroup>
44<col width="18%" />
45<col width="27%" />
46<col width="55%" />
47</colgroup>
48<thead valign="bottom">
49<tr><th>Parameter</th>
50<th>Requirement</th>
51<th>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="lambda-expression-semantics">
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>&lt;x&gt;::type f;
71</pre>
72<table class="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"><a class="reference" href="./metafunction-class.html">Metafunction Class</a>.</td>
77</tr>
78<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" href="./placeholder-expression.html">Placeholder Expression</a> in a general form <tt class="literal"><span class="pre">X&lt;a1,...an&gt;</span></tt>, where
79<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
80to</p>
81<pre class="literal-block">
82typedef <a href="./protect.html" class="identifier">protect</a>&lt; <a href="./bind.html" class="identifier">bind</a>&lt;
83      <a href="./quote.html" class="identifier">quote</a><em>n</em>&lt;X&gt;
84    , <a href="./lambda.html" class="identifier">lambda</a>&lt;a1&gt;::type,<em>...</em> <a href="./lambda.html" class="identifier">lambda</a>&lt;a<em>n</em>&gt;::type
85    &gt; &gt; f;
86</pre>
87<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>
88</td>
89</tr>
90</tbody>
91</table>
92<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
93<pre class="literal-block">
94typedef <a href="./lambda.html" class="identifier">lambda</a>&lt;x,tag&gt;::type f;
95</pre>
96<table class="field-list" frame="void" rules="none">
97<col class="field-name" />
98<col class="field-body" />
99<tbody valign="top">
100<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference" href="./metafunction-class.html">Metafunction Class</a>.</td>
101</tr>
102<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" href="./placeholder-expression.html">Placeholder Expression</a> in a general form <tt class="literal"><span class="pre">X&lt;a1,...an&gt;</span></tt>, where
103<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
104to</p>
105<pre class="literal-block">
106typedef <a href="./protect.html" class="identifier">protect</a>&lt; <a href="./bind.html" class="identifier">bind</a>&lt;
107      <a href="./quote.html" class="identifier">quote</a><em>n</em>&lt;X,tag&gt;
108    , <a href="./lambda.html" class="identifier">lambda</a>&lt;a1,tag&gt;::type,<em>...</em> <a href="./lambda.html" class="identifier">lambda</a>&lt;a<em>n</em>,tag&gt;::type
109    &gt; &gt; f;
110</pre>
111<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>
112</td>
113</tr>
114</tbody>
115</table>
116</div>
117<div class="section" id="lambda-example">
118<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
119<pre class="literal-block">
120template&lt; typename N1, typename N2 &gt; struct int_plus
121    : <a href="./int.html" class="identifier">int_</a>&lt;( N1::value + N2::value )&gt;
122{
123};
124
125typedef <a href="./lambda.html" class="identifier">lambda</a>&lt; int_plus&lt;_1, <a href="./int.html" class="identifier">int_</a>&lt;42&gt; &gt; &gt;::type f1;
126typedef <a href="./bind.html" class="identifier">bind</a>&lt; <a href="./quote.html" class="identifier">quote</a><tt class="literal"><span class="pre">2</span></tt>&lt;int_plus&gt;, _1, <a href="./int.html" class="identifier">int_</a>&lt;42&gt; &gt; f2;
127
128typedef f1::<a href="./apply.html" class="identifier">apply</a>&lt;42&gt;::type r1;
129typedef f2::<a href="./apply.html" class="identifier">apply</a>&lt;42&gt;::type r2;
130
131<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( r1::value, ==, 84 );
132<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( r2::value, ==, 84 );
133</pre>
134</div>
135<div class="section" id="composition-lambda-see-also">
136<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
137<p><a class="reference" href="./composition-and-argument.html">Composition and Argument Binding</a>, <a class="reference" href="./invocation.html">invocation</a>, <a class="reference" href="./placeholders.html">Placeholders</a>, <a class="refentry reference" href="./bind.html"><tt class="refentry literal"><span class="pre">bind</span></tt></a>, <a class="refentry reference" href="./quote.html"><tt class="refentry literal"><span class="pre">quote</span></tt></a>, <a class="refentry reference" href="./protect.html"><tt class="refentry literal"><span class="pre">protect</span></tt></a>, <a class="refentry reference" href="./apply.html"><tt class="refentry literal"><span class="pre">apply</span></tt></a></p>
138<!-- modtime: November 13, 2004 02:51:02 +0000 -->
139<!-- Metafunctions/Composition and Argument Binding//bind |30 -->
140</div>
141</div>
142
143<div class="footer-separator"></div>
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