boost_mpl/doc/refmanual/arg.html

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<div class="section" id="arg">
<h1><a class="toc-backref" href="./composition-and-argument-binding.html#id1533">arg</a></h1>
<div class="section" id="id946">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
template&lt; int n &gt; struct <a href="./arg.html" class="identifier">arg</a>;

template&lt;&gt; struct <a href="./arg.html" class="identifier">arg</a>&lt;1&gt;
{
    template&lt; typename A1,<em>...</em> typename A<em>n</em> = <em>unspecified</em> &gt;
    struct <a href="./apply.html" class="identifier">apply</a>
    {
        typedef A1 type;
    };
};

<em>...</em>

template&lt;&gt; struct <a href="./arg.html" class="identifier">arg</a>&lt;<em>n</em>&gt;
{
    template&lt; typename A1,<em>...</em> typename A<em>n</em> &gt;
    struct <a href="./apply.html" class="identifier">apply</a>
    {
        typedef A<em>n</em> type;
    };
};
</pre>
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<div class="section" id="id947">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p><tt class="literal"><span class="pre"><a href="./arg.html" class="identifier">arg</a>&lt;n&gt;</span></tt> specialization is a <a class="reference internal" 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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<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/arg.hpp" class="header">boost/mpl/arg.hpp</a>&gt;
</pre>
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<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<tr><th class="head">Parameter</th>
<th class="head">Requirement</th>
<th class="head">Description</th>
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<tr><td><tt class="literal"><span class="pre">n</span></tt></td>
<td>An integral constant</td>
<td>A number of argument to return.</td>
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<div class="section" id="id950">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For any integral constant <tt class="literal"><span class="pre">n</span></tt> in the range [1, <a class="reference internal" href="./limit-metafunction-arity.html">BOOST_MPL_LIMIT_METAFUNCTION_ARITY</a>] and
arbitrary types <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>:</p>
<pre class="literal-block">
typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>&lt; <a href="./arg.html" class="identifier">arg</a>&lt;<em>n</em>&gt;,a1,<em>...</em>a<em>n</em> &gt;::type x;
</pre>
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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 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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<div class="section" id="id951">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">5</span></tt>&lt; <a href="./arg.html" class="identifier">arg</a>&lt;1&gt;,bool,char,short,int,long &gt;::type t1;
typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">5</span></tt>&lt; <a href="./arg.html" class="identifier">arg</a>&lt;3&gt;,bool,char,short,int,long &gt;::type t3;

<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; t1, bool &gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; t3, short > ));
</pre>
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<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="./placeholders.html">Placeholders</a>, <a class="reference internal" href="./lambda.html">lambda</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./apply.html">apply</a>, <a class="reference internal" href="./apply-wrap.html">apply_wrap</a></p>
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