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7<title>The MPL Reference Manual: apply_wrap</title>
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11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./apply.html" class="navigation-link">Prev</a>&nbsp;<a href="./unpack-args.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./apply.html" class="navigation-link">Back</a>&nbsp;<a href="./unpack-args.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./invocation.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
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="./invocation.html" class="navigation-link">Invocation</a> / <a href="./apply-wrap.html" class="navigation-link">apply_wrap</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="apply-wrap">
15<h1><a class="toc-backref" href="./invocation.html#id452" name="apply-wrap">apply_wrap</a></h1>
16<div class="section" id="invocation-apply-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19template&lt; 
20      typename F
21    &gt;
22struct apply_wrap0
23{
24    typedef <em>unspecified</em> type;
25};
26
27template&lt; 
28      typename F, typename A1
29    &gt;
30struct apply_wrap1
31{
32    typedef <em>unspecified</em> type;
33};
34
35<em>...</em>
36
37template&lt; 
38      typename F, typename A1,<em>...</em> typename An
39    &gt;
40struct <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>
41{
42    typedef <em>unspecified</em> type;
43};
44</pre>
45</div>
46<div class="section" id="invocation-apply-description">
47<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
48<p>Invokes a <a class="reference" href="./metafunction-class.html">Metafunction Class</a> <tt class="literal"><span class="pre">F</span></tt> with arguments <tt class="literal"><span class="pre">A1</span></tt>,... <tt class="literal"><span class="pre">An</span></tt>.</p>
49<p>In essence, <tt class="literal"><span class="pre"><a href="./apply-wrap.html" class="identifier">apply_wrap</a></span></tt> forms are nothing more than syntactic wrappers around
50<tt class="literal"><span class="pre">F::<a href="./apply.html" class="identifier">apply</a>&lt;A1,...</span> <span class="pre">An&gt;::type</span></tt> / <tt class="literal"><span class="pre">F::<a href="./apply.html" class="identifier">apply</a>::type</span></tt> expressions (hence the name).
51They provide a more concise notation and higher portability than their
52underlaying constructs at the cost of an extra template instantiation.</p>
53</div>
54<div class="section" id="invocation-apply-header">
55<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
56<pre class="literal-block">
57#include &lt;<a href="../../../../boost/mpl/apply_wrap.hpp" class="header">boost/mpl/apply_wrap.hpp</a>&gt;
58</pre>
59</div>
60<div class="section" id="invocation-apply-parameters">
61<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
62<table border="1" class="table">
63<colgroup>
64<col width="15%" />
65<col width="36%" />
66<col width="48%" />
67</colgroup>
68<thead valign="bottom">
69<tr><th>Parameter</th>
70<th>Requirement</th>
71<th>Description</th>
72</tr>
73</thead>
74<tbody valign="top">
75<tr><td><tt class="literal"><span class="pre">F</span></tt></td>
76<td><a class="reference" href="./metafunction-class.html">Metafunction Class</a></td>
77<td>A metafunction class to invoke.</td>
78</tr>
79<tr><td><tt class="literal"><span class="pre">A1</span></tt>,... <tt class="literal"><span class="pre">An</span></tt></td>
80<td>Any type</td>
81<td>Invocation arguments.</td>
82</tr>
83</tbody>
84</table>
85</div>
86<div class="section" id="invocation-apply-expression-semantics">
87<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
88<p>For any <a class="reference" href="./metafunction-class.html">Metafunction Class</a> <tt class="literal"><span class="pre">f</span></tt> and arbitrary types <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>:</p>
89<pre class="literal-block">
90typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>&lt;f,a1,<em>...</em>an&gt;::type t;
91</pre>
92<table class="field-list" frame="void" rules="none">
93<col class="field-name" />
94<col class="field-body" />
95<tbody valign="top">
96<tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td>
97</tr>
98<tr class="field"><th class="field-name">Semantics:</th><td class="field-body">If <tt class="literal"><span class="pre">n</span> <span class="pre">&gt;</span> <span class="pre">0</span></tt>, equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre">f::<a href="./apply.html" class="identifier">apply</a>&lt;a1,...</span> <span class="pre">an&gt;::type</span> <span class="pre">t;</span></tt>,
99otherwise equivalent to either <tt class="literal"><span class="pre">typedef</span> <span class="pre">f::<a href="./apply.html" class="identifier">apply</a>::type</span> <span class="pre">t;</span></tt> or
100<tt class="literal"><span class="pre">typedef</span> <span class="pre">f::<a href="./apply.html" class="identifier">apply</a>&lt;&gt;::type</span> <span class="pre">t;</span></tt> depending on whether <tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a></span></tt> is
101a class or a class template.</td>
102</tr>
103</tbody>
104</table>
105</div>
106<div class="section" id="invocation-apply-example">
107<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
108<pre class="literal-block">
109struct f0
110{
111    template&lt; typename T = int &gt; struct <a href="./apply.html" class="identifier">apply</a>
112    {
113        typedef char type;
114    };
115};
116   
117struct g0
118{
119    struct <a href="./apply.html" class="identifier">apply</a> { typedef char type; };
120};
121
122struct f2
123{
124    template&lt; typename T1, typename T2 &gt; struct <a href="./apply.html" class="identifier">apply</a>
125    {
126        typedef T2 type;
127    };
128};
129
130
131typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">0</span></tt>&lt; f0 &gt;::type r1;
132typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">0</span></tt>&lt; g0 &gt;::type r2;
133typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">2</span></tt>&lt; f2,int,char &gt;::type r3;
134
135<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r1,char&gt; ));
136<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r2,char&gt; ));
137<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r3,char&gt; ));
138</pre>
139</div>
140<div class="section" id="invocation-apply-see-also">
141<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
142<p><a class="reference" href="./metafunctions.html">Metafunctions</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="./quote.html"><tt class="refentry literal"><span class="pre">quote</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="./protect.html"><tt class="refentry literal"><span class="pre">protect</span></tt></a></p>
143<!-- modtime: November 10, 2004 04:46:09 +0000 -->
144<!-- Metafunctions/Invocation//unpack_args |30 -->
145</div>
146</div>
147
148<div class="footer-separator"></div>
149<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./apply.html" class="navigation-link">Prev</a>&nbsp;<a href="./unpack-args.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./apply.html" class="navigation-link">Back</a>&nbsp;<a href="./unpack-args.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./invocation.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
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