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114 lines
7.7 KiB
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<title>The MPL Reference Manual: arg</title>
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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="./quote.html" class="navigation-link">Prev</a> <a href="./protect.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./quote.html" class="navigation-link">Back</a> <a href="./protect.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./composition-and-argument.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.html" class="navigation-link">Composition and Argument Binding</a> / <a href="./arg.html" class="navigation-link">arg</a></td>
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</tr></table><div class="header-separator"></div>
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<div class="section" id="arg">
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<h1><a class="toc-backref" href="./composition-and-argument.html#id459" name="arg">arg</a></h1>
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<div class="section" id="arg-synopsis">
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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< int n > struct <a href="./arg.html" class="identifier">arg</a>;
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template<> struct <a href="./arg.html" class="identifier">arg</a><1>
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{
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template< typename A1,<em>...</em> typename A<em>n</em> = <em>unspecified</em> >
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struct <a href="./apply.html" class="identifier">apply</a>
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{
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typedef A1 type;
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};
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};
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<em>...</em>
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template<> struct <a href="./arg.html" class="identifier">arg</a><<em>n</em>>
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{
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template< typename A1,<em>...</em> typename A<em>n</em> >
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struct <a href="./apply.html" class="identifier">apply</a>
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{
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typedef A<em>n</em> type;
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};
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};
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</pre>
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</div>
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<div class="section" id="arg-description">
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<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
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<p><tt class="literal"><span class="pre"><a href="./arg.html" class="identifier">arg</a><n></span></tt> specialization is a <a class="reference" href="./metafunction-class.html">Metafunction Class</a> that return the <tt class="literal"><span class="pre">n</span></tt>th of its arguments.</p>
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</div>
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<div class="section" id="arg-header">
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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/arg.hpp" class="header">boost/mpl/arg.hpp</a>>
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</pre>
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</div>
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<div class="section" id="arg-parameters">
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<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<table border="1" class="table">
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<colgroup>
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<col width="15%" />
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<col width="36%" />
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<col width="48%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th>Parameter</th>
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<th>Requirement</th>
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<th>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">n</span></tt></td>
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<td>An integral constant</td>
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<td>A number of argument to return.</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="arg-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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<p>For any integral constant <tt class="literal"><span class="pre">n</span></tt> in the range [1, <a class="refentry reference" href="./limit-metafunction-arity.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_LIMIT_METAFUNCTION_ARITY</span></tt></a>] and
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arbitrary types <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>:</p>
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<pre class="literal-block">
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typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>< <a href="./arg.html" class="identifier">arg</a><<em>n</em>>,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">Return type:</th><td class="field-body">A type.</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 identical to <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="arg-example">
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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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typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">5</span></tt>< <a href="./arg.html" class="identifier">arg</a><1>,bool,char,short,int,long >::type t1;
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typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">5</span></tt>< <a href="./arg.html" class="identifier">arg</a><3>,bool,char,short,int,long >::type t3;
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<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< t1, bool > ));
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<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< t3, short > ));
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</pre>
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</div>
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<div class="section" id="arg-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="./composition-and-argument.html">Composition and Argument Binding</a>, <a class="reference" href="./placeholders.html">Placeholders</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>, <a class="refentry reference" href="./apply.html"><tt class="refentry literal"><span class="pre">apply</span></tt></a>, <a class="refentry reference" href="./apply-wrap.html"><tt class="refentry literal"><span class="pre">apply_wrap</span></tt></a></p>
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