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128 lines
9.1 KiB
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<?xml version="1.0" encoding="utf-8" ?>
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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 name="generator" content="Docutils 0.3.6: http://docutils.sourceforge.net/" />
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<title>The MPL Reference Manual: Metafunction</title>
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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="./metafunctions-concepts.html" class="navigation-link">Prev</a> <a href="./metafunction-class.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group">Back <a href="./metafunction-class.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./metafunctions-concepts.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="./metafunctions-concepts.html" class="navigation-link">Concepts</a> / <a href="./metafunction.html" class="navigation-link">Metafunction</a></td>
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</tr></table><div class="header-separator"></div>
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<div class="section" id="metafunction">
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<h1><a class="toc-backref" href="./metafunctions-concepts.html#id438" name="metafunction">Metafunction</a></h1>
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<div class="section" id="metafunction-description">
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<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
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<a class="target" id="nullary-metafunction" name="nullary-metafunction"></a><p>A <em>metafunction</em> is a class or a class template that represents a
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function invocable at compile-time. An non-nullary metafunction is
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invoked by instantiating the class template with particular
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template parameters (metafunction arguments); the result of the
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metafunction application is accessible through the instantiation's
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nested <tt class="literal"><span class="pre">type</span></tt> typedef. All metafunction's arguments must be types
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(i.e. only <em>type template parameters</em> are allowed). A metafunction
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can have a variable number of parameters. A <em>nullary metafunction</em> is
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represented as a (template) class with a nested <tt class="literal"><span class="pre">type</span></tt> typename
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member.</p>
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</div>
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<div class="section" id="metafunction-expression-requirements">
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<h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3>
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<p>In the following table and subsequent specifications, <tt class="literal"><span class="pre">f</span></tt> is a <a class="reference" href="./metafunction.html">Metafunction</a>.</p>
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<table border="1" class="table">
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<colgroup>
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<col width="38%" />
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<col width="28%" />
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<col width="33%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th>Expression</th>
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<th>Type</th>
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<th>Complexity</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">f::type</span></tt></td>
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<td>Any type</td>
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<td>Unspecified.</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre">f<>::type</span></tt></td>
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<td>Any type</td>
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<td>Unspecified.</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre">f<a1,..,an>::type</span></tt></td>
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<td>Any type</td>
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<td>Unspecified.</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="metafunction-expression-semantics">
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<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
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<pre class="literal-block">
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typedef f::type x;
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</pre>
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<table class="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">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is a nullary <a class="reference" href="./metafunction.html">Metafunction</a>; <tt class="literal"><span class="pre">f::type</span></tt> is a <em>type-name</em>.</td>
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</tr>
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<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction invocation.</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 f<>::type x;
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</pre>
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<table class="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">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is a nullary <a class="reference" href="./metafunction.html">Metafunction</a>; <tt class="literal"><span class="pre">f<>::type</span></tt> is a <em>type-name</em>.</td>
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</tr>
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<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction invocation.</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 f<a1,<em>...</em> a<em>n</em>>::type x;
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</pre>
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<table class="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">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is an <em>n</em>-ary <a class="reference" href="./metafunction.html">Metafunction</a>; <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt> are types;
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<tt class="literal"><span class="pre">f<a1,...an>::type</span></tt> is a <em>type-name</em>.</td>
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</tr>
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<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction invocation
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with the actual arguments <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>.</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="metafunction-models">
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<h3><a class="subsection-title" href="#models" name="models">Models</a></h3>
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<ul class="simple">
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<li><a class="refentry reference" href="./identity.html"><tt class="refentry literal"><span class="pre">identity</span></tt></a></li>
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<li><a class="refentry reference" href="./plus.html"><tt class="refentry literal"><span class="pre">plus</span></tt></a></li>
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<li><a class="refentry reference" href="./begin.html"><tt class="refentry literal"><span class="pre">begin</span></tt></a></li>
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<li><a class="refentry reference" href="./insert.html"><tt class="refentry literal"><span class="pre">insert</span></tt></a></li>
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<li><a class="refentry reference" href="./fold.html"><tt class="refentry literal"><span class="pre">fold</span></tt></a></li>
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</ul>
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</div>
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<div class="section" id="metafunction-see-also">
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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" href="./metafunctions.html">Metafunctions</a>, <a class="reference" href="./metafunction-class.html">Metafunction Class</a>, <a class="reference" href="./lambda-expression.html">Lambda Expression</a>, <a class="reference" href="./invocation.html">invocation</a>, <a class="refentry reference" href="./apply.html"><tt class="refentry literal"><span class="pre">apply</span></tt></a>, <a class="refentry reference" href="./lambda.html"><tt class="refentry literal"><span class="pre">lambda</span></tt></a>, <a class="refentry reference" href="./bind.html"><tt class="refentry literal"><span class="pre">bind</span></tt></a></p>
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<!-- modtime: November 10, 2004 04:37:49 +0000 -->
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<!-- Metafunctions/Concepts//Metafunction Class |20 -->
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