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7<title>The MPL Reference Manual: arg</title>
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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.html" class="navigation-link">Composition and Argument Binding</a> / <a href="./arg.html" class="navigation-link">arg</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="arg">
15<h1><a class="toc-backref" href="./composition-and-argument.html#id459" name="arg">arg</a></h1>
16<div class="section" id="arg-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19template&lt; int n &gt; struct <a href="./arg.html" class="identifier">arg</a>;
20
21template&lt;&gt; struct <a href="./arg.html" class="identifier">arg</a>&lt;1&gt;
22{
23    template&lt; typename A1,<em>...</em> typename A<em>n</em> = <em>unspecified</em> &gt;
24    struct <a href="./apply.html" class="identifier">apply</a>
25    {
26        typedef A1 type;
27    };
28};
29
30<em>...</em>
31
32template&lt;&gt; struct <a href="./arg.html" class="identifier">arg</a>&lt;<em>n</em>&gt;
33{
34    template&lt; typename A1,<em>...</em> typename A<em>n</em> &gt;
35    struct <a href="./apply.html" class="identifier">apply</a>
36    {
37        typedef A<em>n</em> type;
38    };
39};
40</pre>
41</div>
42<div class="section" id="arg-description">
43<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
44<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" href="./metafunction-class.html">Metafunction Class</a> that return the <tt class="literal"><span class="pre">n</span></tt>th of its arguments.</p>
45</div>
46<div class="section" id="arg-header">
47<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
48<pre class="literal-block">
49#include &lt;<a href="../../../../boost/mpl/arg.hpp" class="header">boost/mpl/arg.hpp</a>&gt;
50</pre>
51</div>
52<div class="section" id="arg-parameters">
53<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
54<table border="1" class="table">
55<colgroup>
56<col width="15%" />
57<col width="36%" />
58<col width="48%" />
59</colgroup>
60<thead valign="bottom">
61<tr><th>Parameter</th>
62<th>Requirement</th>
63<th>Description</th>
64</tr>
65</thead>
66<tbody valign="top">
67<tr><td><tt class="literal"><span class="pre">n</span></tt></td>
68<td>An integral constant</td>
69<td>A number of argument to return.</td>
70</tr>
71</tbody>
72</table>
73</div>
74<div class="section" id="arg-expression-semantics">
75<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
76<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
77arbitrary types <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>:</p>
78<pre class="literal-block">
79typedef <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;
80</pre>
81<table class="field-list" frame="void" rules="none">
82<col class="field-name" />
83<col class="field-body" />
84<tbody valign="top">
85<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
86</tr>
87<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>
88</tr>
89</tbody>
90</table>
91</div>
92<div class="section" id="arg-example">
93<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
94<pre class="literal-block">
95typedef <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;
96typedef <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;
97
98<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; t1, bool &gt; ));
99<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; t3, short > ));
100</pre>
101</div>
102<div class="section" id="arg-see-also">
103<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
104<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>
105<!-- modtime: November 13, 2004 18:35:04 +0000 -->
106<!-- Metafunctions/Composition and Argument Binding//protect |60 -->
107</div>
108</div>
109
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