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- <title>The MPL Reference Manual: lambda</title>
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- <div class="section" id="lambda">
- <h1><a class="toc-backref" href="./composition-and-argument-binding.html#id1530">lambda</a></h1>
- <div class="section" id="id922">
- <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
- <pre class="literal-block">
- template<
- typename X
- , typename Tag = <em>unspecified</em>
- >
- struct <a href="./lambda.html" class="identifier">lambda</a>
- {
- typedef <em>unspecified</em> type;
- };
- </pre>
- </div>
- <div class="section" id="id923">
- <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
- <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
- <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>
- </div>
- <div class="section" id="id924">
- <h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
- <pre class="literal-block">
- #include <<a href="../../../../boost/mpl/lambda.hpp" class="header">boost/mpl/lambda.hpp</a>>
- </pre>
- </div>
- <div class="section" id="id925">
- <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
- <table border="1" class="docutils table">
- <colgroup>
- <col width="18%" />
- <col width="27%" />
- <col width="55%" />
- </colgroup>
- <thead valign="bottom">
- <tr><th class="head">Parameter</th>
- <th class="head">Requirement</th>
- <th class="head">Description</th>
- </tr>
- </thead>
- <tbody valign="top">
- <tr><td><tt class="literal"><span class="pre">X</span></tt></td>
- <td>Any type</td>
- <td>An expression to transform.</td>
- </tr>
- <tr><td><tt class="literal"><span class="pre">Tag</span></tt></td>
- <td>Any type</td>
- <td>A tag determining transform semantics.</td>
- </tr>
- </tbody>
- </table>
- </div>
- <div class="section" id="id926">
- <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
- <p>For arbitrary types <tt class="literal"><span class="pre">x</span></tt> and <tt class="literal"><span class="pre">tag</span></tt>:</p>
- <pre class="literal-block">
- typedef <a href="./lambda.html" class="identifier">lambda</a><x>::type f;
- </pre>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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>
- </td>
- </tr>
- <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
- <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
- to</p>
- <pre class="literal-block">
- typedef <a href="./protect.html" class="identifier">protect</a>< <a href="./bind.html" class="identifier">bind</a><
- <a href="./quote.html" class="identifier">quote</a><em>n</em><X>
- , <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
- > > f;
- </pre>
- <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>
- </td>
- </tr>
- </tbody>
- </table>
- <!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
- <pre class="literal-block">
- typedef <a href="./lambda.html" class="identifier">lambda</a><x,tag>::type f;
- </pre>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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>
- </td>
- </tr>
- <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
- <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
- to</p>
- <pre class="literal-block">
- typedef <a href="./protect.html" class="identifier">protect</a>< <a href="./bind.html" class="identifier">bind</a><
- <a href="./quote.html" class="identifier">quote</a><em>n</em><X,tag>
- , <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
- > > f;
- </pre>
- <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>
- </td>
- </tr>
- </tbody>
- </table>
- </div>
- <div class="section" id="id927">
- <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
- <pre class="literal-block">
- template< typename N1, typename N2 > struct int_plus
- : <a href="./int.html" class="identifier">int_</a><( N1::value + N2::value )>
- {
- };
- 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;
- 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;
- typedef f1::<a href="./apply.html" class="identifier">apply</a><42>::type r1;
- typedef f2::<a href="./apply.html" class="identifier">apply</a><42>::type r2;
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( r1::value, ==, 84 );
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( r2::value, ==, 84 );
- </pre>
- </div>
- <div class="section" id="id928">
- <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
- <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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- <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
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