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10<title>The MPL Reference Manual: arg</title>
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15<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>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="arg">
18<h1><a class="toc-backref" href="./composition-and-argument.html#id459" name="arg">arg</a></h1>
19<div class="section" id="arg-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22template&lt; int n &gt; struct <a href="./arg.html" class="identifier">arg</a>;
23
24template&lt;&gt; struct <a href="./arg.html" class="identifier">arg</a>&lt;1&gt;
25{
26    template&lt; typename A1,<em>...</em> typename A<em>n</em> = <em>unspecified</em> &gt;
27    struct <a href="./apply.html" class="identifier">apply</a>
28    {
29        typedef A1 type;
30    };
31};
32
33<em>...</em>
34
35template&lt;&gt; struct <a href="./arg.html" class="identifier">arg</a>&lt;<em>n</em>&gt;
36{
37    template&lt; typename A1,<em>...</em> typename A<em>n</em> &gt;
38    struct <a href="./apply.html" class="identifier">apply</a>
39    {
40        typedef A<em>n</em> type;
41    };
42};
43</pre>
44</div>
45<div class="section" id="arg-description">
46<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
47<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>
48</div>
49<div class="section" id="arg-header">
50<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
51<pre class="literal-block">
52#include &lt;<a href="../../../../boost/mpl/arg.hpp" class="header">boost/mpl/arg.hpp</a>&gt;
53</pre>
54</div>
55<div class="section" id="arg-parameters">
56<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
57<table border="1" class="table">
58<colgroup>
59<col width="15%" />
60<col width="36%" />
61<col width="48%" />
62</colgroup>
63<thead valign="bottom">
64<tr><th>Parameter</th>
65<th>Requirement</th>
66<th>Description</th>
67</tr>
68</thead>
69<tbody valign="top">
70<tr><td><tt class="literal"><span class="pre">n</span></tt></td>
71<td>An integral constant</td>
72<td>A number of argument to return.</td>
73</tr>
74</tbody>
75</table>
76</div>
77<div class="section" id="arg-expression-semantics">
78<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
79<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
80arbitrary types <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>:</p>
81<pre class="literal-block">
82typedef <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;
83</pre>
84<table class="field-list" frame="void" rules="none">
85<col class="field-name" />
86<col class="field-body" />
87<tbody valign="top">
88<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
89</tr>
90<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>
91</tr>
92</tbody>
93</table>
94</div>
95<div class="section" id="arg-example">
96<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
97<pre class="literal-block">
98typedef <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;
99typedef <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;
100
101<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; t1, bool &gt; ));
102<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; t3, short > ));
103</pre>
104</div>
105<div class="section" id="arg-see-also">
106<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
107<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>
108<!-- modtime: November 13, 2004 18:35:04 +0000 -->
109<!-- Metafunctions/Composition and Argument Binding//protect |60 -->
110</div>
111</div>
112
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