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<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>
<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>
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<div class="section" id="apply-wrap">
<h1><a class="toc-backref" href="./invocation.html#id1526">apply_wrap</a></h1>
<div class="section" id="id894">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
template&lt;
      typename F
    &gt;
struct apply_wrap0
{
    typedef <em>unspecified</em> type;
};

template&lt;
      typename F, typename A1
    &gt;
struct apply_wrap1
{
    typedef <em>unspecified</em> type;
};

<em>...</em>

template&lt;
      typename F, typename A1,<em>...</em> typename An
    &gt;
struct <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>
{
    typedef <em>unspecified</em> type;
};
</pre>
</div>
<div class="section" id="id895">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p>Invokes a <a class="reference internal" 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>
<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
<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).
They provide a more concise notation and higher portability than their
underlaying constructs at the cost of an extra template instantiation.</p>
</div>
<div class="section" id="id896">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/apply_wrap.hpp" class="header">boost/mpl/apply_wrap.hpp</a>&gt;
</pre>
</div>
<div class="section" id="id897">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
<table border="1" class="docutils table">
<colgroup>
<col width="15%" />
<col width="36%" />
<col width="48%" />
</colgroup>
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<tr><th class="head">Parameter</th>
<th class="head">Requirement</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">F</span></tt></td>
<td><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a></td>
<td>A metafunction class to invoke.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">A1</span></tt>,... <tt class="literal"><span class="pre">An</span></tt></td>
<td>Any type</td>
<td>Invocation arguments.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id898">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For any <a class="reference internal" 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>
<pre class="literal-block">
typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>&lt;f,a1,<em>...</em>an&gt;::type t;
</pre>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td>
</tr>
<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>,
otherwise 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
<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
a class or a class template.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id899">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
struct f0
{
    template&lt; typename T = int &gt; struct <a href="./apply.html" class="identifier">apply</a>
    {
        typedef char type;
    };
};

struct g0
{
    struct <a href="./apply.html" class="identifier">apply</a> { typedef char type; };
};

struct f2
{
    template&lt; typename T1, typename T2 &gt; struct <a href="./apply.html" class="identifier">apply</a>
    {
        typedef T2 type;
    };
};


typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">0</span></tt>&lt; f0 &gt;::type r1;
typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">0</span></tt>&lt; g0 &gt;::type r2;
typedef <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;

<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r1,char&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r2,char&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r3,char&gt; ));
</pre>
</div>
<div class="section" id="id900">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./invocation.html">invocation</a>, <a class="reference internal" href="./apply.html">apply</a>, <a class="reference internal" href="./lambda.html">lambda</a>, <a class="reference internal" href="./quote.html">quote</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./protect.html">protect</a></p>
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