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10<title>The MPL Reference Manual: apply_wrap</title>
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13<body class="docframe refmanual">
14<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>
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="./invocation.html" class="navigation-link">Invocation</a> / <a href="./apply-wrap.html" class="navigation-link">apply_wrap</a></td>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="apply-wrap">
18<h1><a class="toc-backref" href="./invocation.html#id452" name="apply-wrap">apply_wrap</a></h1>
19<div class="section" id="invocation-apply-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22template&lt; 
23      typename F
24    &gt;
25struct apply_wrap0
26{
27    typedef <em>unspecified</em> type;
28};
29
30template&lt; 
31      typename F, typename A1
32    &gt;
33struct apply_wrap1
34{
35    typedef <em>unspecified</em> type;
36};
37
38<em>...</em>
39
40template&lt; 
41      typename F, typename A1,<em>...</em> typename An
42    &gt;
43struct <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>
44{
45    typedef <em>unspecified</em> type;
46};
47</pre>
48</div>
49<div class="section" id="invocation-apply-description">
50<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
51<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>
52<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
53<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).
54They provide a more concise notation and higher portability than their
55underlaying constructs at the cost of an extra template instantiation.</p>
56</div>
57<div class="section" id="invocation-apply-header">
58<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
59<pre class="literal-block">
60#include &lt;<a href="../../../../boost/mpl/apply_wrap.hpp" class="header">boost/mpl/apply_wrap.hpp</a>&gt;
61</pre>
62</div>
63<div class="section" id="invocation-apply-parameters">
64<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
65<table border="1" class="table">
66<colgroup>
67<col width="15%" />
68<col width="36%" />
69<col width="48%" />
70</colgroup>
71<thead valign="bottom">
72<tr><th>Parameter</th>
73<th>Requirement</th>
74<th>Description</th>
75</tr>
76</thead>
77<tbody valign="top">
78<tr><td><tt class="literal"><span class="pre">F</span></tt></td>
79<td><a class="reference" href="./metafunction-class.html">Metafunction Class</a></td>
80<td>A metafunction class to invoke.</td>
81</tr>
82<tr><td><tt class="literal"><span class="pre">A1</span></tt>,... <tt class="literal"><span class="pre">An</span></tt></td>
83<td>Any type</td>
84<td>Invocation arguments.</td>
85</tr>
86</tbody>
87</table>
88</div>
89<div class="section" id="invocation-apply-expression-semantics">
90<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
91<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>
92<pre class="literal-block">
93typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>&lt;f,a1,<em>...</em>an&gt;::type t;
94</pre>
95<table class="field-list" frame="void" rules="none">
96<col class="field-name" />
97<col class="field-body" />
98<tbody valign="top">
99<tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td>
100</tr>
101<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>,
102otherwise 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
103<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
104a class or a class template.</td>
105</tr>
106</tbody>
107</table>
108</div>
109<div class="section" id="invocation-apply-example">
110<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
111<pre class="literal-block">
112struct f0
113{
114    template&lt; typename T = int &gt; struct <a href="./apply.html" class="identifier">apply</a>
115    {
116        typedef char type;
117    };
118};
119   
120struct g0
121{
122    struct <a href="./apply.html" class="identifier">apply</a> { typedef char type; };
123};
124
125struct f2
126{
127    template&lt; typename T1, typename T2 &gt; struct <a href="./apply.html" class="identifier">apply</a>
128    {
129        typedef T2 type;
130    };
131};
132
133
134typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">0</span></tt>&lt; f0 &gt;::type r1;
135typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">0</span></tt>&lt; g0 &gt;::type r2;
136typedef <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;
137
138<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r1,char&gt; ));
139<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r2,char&gt; ));
140<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r3,char&gt; ));
141</pre>
142</div>
143<div class="section" id="invocation-apply-see-also">
144<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
145<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>
146<!-- modtime: November 10, 2004 04:46:09 +0000 -->
147<!-- Metafunctions/Invocation//unpack_args |30 -->
148</div>
149</div>
150
151<div class="footer-separator"></div>
152<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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