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150 lines
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HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" />
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<title>The MPL Reference Manual: lambda</title>
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<link rel="stylesheet" href="../style.css" type="text/css" />
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</head>
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<body class="docframe refmanual">
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<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>
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<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>
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</tr></table><div class="header-separator"></div>
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<div class="section" id="lambda">
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<h1><a class="toc-backref" href="./composition-and-argument-binding.html#id1530">lambda</a></h1>
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<div class="section" id="id922">
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<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
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<pre class="literal-block">
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template<
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typename X
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, typename Tag = <em>unspecified</em>
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>
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struct <a href="./lambda.html" class="identifier">lambda</a>
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{
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typedef <em>unspecified</em> type;
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};
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</pre>
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</div>
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<div class="section" id="id923">
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<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
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<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
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<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>
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</div>
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<div class="section" id="id924">
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<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
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<pre class="literal-block">
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#include <<a href="../../../../boost/mpl/lambda.hpp" class="header">boost/mpl/lambda.hpp</a>>
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</pre>
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</div>
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<div class="section" id="id925">
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<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<table border="1" class="docutils table">
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<colgroup>
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<col width="18%" />
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<col width="27%" />
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<col width="55%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th class="head">Parameter</th>
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<th class="head">Requirement</th>
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<th class="head">Description</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr><td><tt class="literal"><span class="pre">X</span></tt></td>
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<td>Any type</td>
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<td>An expression to transform.</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre">Tag</span></tt></td>
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<td>Any type</td>
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<td>A tag determining transform semantics.</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="id926">
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<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
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<p>For arbitrary types <tt class="literal"><span class="pre">x</span></tt> and <tt class="literal"><span class="pre">tag</span></tt>:</p>
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<pre class="literal-block">
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typedef <a href="./lambda.html" class="identifier">lambda</a><x>::type f;
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</pre>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</td>
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</tr>
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<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
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<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
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to</p>
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<pre class="literal-block">
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typedef <a href="./protect.html" class="identifier">protect</a>< <a href="./bind.html" class="identifier">bind</a><
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<a href="./quote.html" class="identifier">quote</a><em>n</em><X>
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, <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
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> > f;
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</pre>
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<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>
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</td>
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</tr>
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</tbody>
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</table>
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<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
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<pre class="literal-block">
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typedef <a href="./lambda.html" class="identifier">lambda</a><x,tag>::type f;
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</pre>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</td>
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</tr>
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<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
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<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
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to</p>
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<pre class="literal-block">
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typedef <a href="./protect.html" class="identifier">protect</a>< <a href="./bind.html" class="identifier">bind</a><
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<a href="./quote.html" class="identifier">quote</a><em>n</em><X,tag>
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, <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
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> > f;
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</pre>
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<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>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="id927">
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<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
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<pre class="literal-block">
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template< typename N1, typename N2 > struct int_plus
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: <a href="./int.html" class="identifier">int_</a><( N1::value + N2::value )>
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{
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};
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typedef <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;
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typedef <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;
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typedef f1::<a href="./apply.html" class="identifier">apply</a><42>::type r1;
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typedef f2::<a href="./apply.html" class="identifier">apply</a><42>::type r2;
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<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( r1::value, ==, 84 );
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<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( r2::value, ==, 84 );
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</pre>
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</div>
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<div class="section" id="id928">
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<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
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<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>
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<!-- Metafunctions/Composition and Argument Binding//bind |30 -->
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</div>
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</div>
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<div class="footer-separator"></div>
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<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>
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<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file 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>
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