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| <title>The MPL Reference Manual: lambda</title> |
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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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| <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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