ceph/src/boost/libs/mpl/doc/refmanual/lambda.html

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   7 <title>The MPL Reference Manual: lambda</title>
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  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-binding.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-binding.html" class="navigation-link">Composition and Argument Binding</a> / <a href="./lambda.html" class="navigation-link">lambda</a></td>
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  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">
  19 template&lt;
  20       typename X
  21     , typename Tag = <em>unspecified</em>
  22     &gt;
  23 struct <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 &lt;<a href="../../../../boost/mpl/lambda.hpp" class="header">boost/mpl/lambda.hpp</a>&gt;
  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">
  70 typedef <a href="./lambda.html" class="identifier">lambda</a>&lt;x&gt;::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&lt;a1,...an&gt;</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
  81 to</p>
  82 <pre class="literal-block">
  83 typedef <a href="./protect.html" class="identifier">protect</a>&lt; <a href="./bind.html" class="identifier">bind</a>&lt;
  84       <a href="./quote.html" class="identifier">quote</a><em>n</em>&lt;X&gt;
  85     , <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
  86     &gt; &gt; 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">
  95 typedef <a href="./lambda.html" class="identifier">lambda</a>&lt;x,tag&gt;::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&lt;a1,...an&gt;</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
 106 to</p>
 107 <pre class="literal-block">
 108 typedef <a href="./protect.html" class="identifier">protect</a>&lt; <a href="./bind.html" class="identifier">bind</a>&lt;
 109       <a href="./quote.html" class="identifier">quote</a><em>n</em>&lt;X,tag&gt;
 110     , <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
 111     &gt; &gt; 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">
 122 template&lt; typename N1, typename N2 &gt; struct int_plus
 123     : <a href="./int.html" class="identifier">int_</a>&lt;( N1::value + N2::value )&gt;
 124 {
 125 };
 126
 127 typedef <a href="./lambda.html" class="identifier">lambda</a>&lt; int_plus&lt;<a href="./placeholders.html" class="identifier">_1</a>, <a href="./int.html" class="identifier">int_</a>&lt;42&gt; &gt; &gt;::type f1;
 128 typedef <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;, <a href="./placeholders.html" class="identifier">_1</a>, <a href="./int.html" class="identifier">int_</a>&lt;42&gt; &gt; f2;
 129
 130 typedef f1::<a href="./apply.html" class="identifier">apply</a>&lt;42&gt;::type r1;
 131 typedef f2::<a href="./apply.html" class="identifier">apply</a>&lt;42&gt;::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
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 146 <td><div class="copyright-footer"><div class="copyright">Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams</div>
 147 Distributed under the Boost Software License, Version 1.0. (See accompanying
 148 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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