boost_mpl/doc/refmanual/protect.html

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<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="./protect.html" class="navigation-link">protect</a></td>
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<div class="section" id="protect">
<h1><a class="toc-backref" href="./composition-and-argument.html#id460" name="protect">protect</a></h1>
<div class="section" id="protect-synopsis">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
template&lt; 
      typename F
    &gt;
struct <a href="./protect.html" class="identifier">protect</a>
{
    // <em>unspecified</em>
    // <em>...</em>
};
</pre>
</div>
<div class="section" id="protect-description">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p><tt class="literal"><span class="pre"><a href="./protect.html" class="identifier">protect</a></span></tt> is an identity wrapper for a <a class="reference" href="./metafunction-class.html">Metafunction Class</a> that prevents
its argument from being recognized as a <a class="reference" href="./terminology.html#bind-expression">bind expression</a>.</p>
</div>
<div class="section" id="protect-header">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/protect.hpp" class="header">boost/mpl/protect.hpp</a>&gt;
</pre>
</div>
<div class="section" id="protect-parameters">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<colgroup>
<col width="19%" />
<col width="33%" />
<col width="48%" />
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<thead valign="bottom">
<tr><th>Parameter</th>
<th>Requirement</th>
<th>Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">F</span></tt></td>
<td><a class="reference" href="./metafunction-class.html">Metafunction Class</a></td>
<td>A metafunction class to wrap.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="protect-expression-semantics">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For any <a class="reference" href="./metafunction-class.html">Metafunction Class</a> <tt class="literal"><span class="pre">f</span></tt>:</p>
<pre class="literal-block">
typedef <a href="./protect.html" class="identifier">protect</a>&lt;f&gt; g;
</pre>
<table class="field-list" frame="void" rules="none">
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<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference" href="./metafunction-class.html">Metafunction Class</a>.</td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">If <tt class="literal"><span class="pre">f</span></tt> is a <a class="reference" href="./terminology.html#bind-expression">bind expression</a>, equivalent to</p>
<pre class="literal-block">
struct g
{
    template&lt; 
          typename U1 = <em>unspecified</em>,<em>...</em> typename U<em>n</em> = <em>unspecified</em>
        &gt;
    struct <a href="./apply.html" class="identifier">apply</a>
        : <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>&lt;f,U1,<em>...</em>U<em>n</em>&gt;
    {
    };
};
</pre>
<p class="last">otherwise equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre">f</span> <span class="pre">g;</span></tt>.</p>
</td>
</tr>
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</div>
<div class="section" id="protect-example">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
FIXME

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

typedef <a href="./bind.html" class="identifier">bind</a>&lt;_1, <a href="./protect.html" class="identifier">protect</a>&lt; <a href="./bind.html" class="identifier">bind</a>&lt;f,_1,_2&gt; &gt; &gt;

typedef apply_wrap0&lt; f0 &gt;::type r1;
typedef apply_wrap0&lt; g0 &gt;::type r2;
typedef apply_wrap2&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="protect-see-also">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference" href="./composition-and-argument.html">Composition and Argument Binding</a>, <a class="reference" href="./invocation.html">invocation</a>, <a class="refentry reference" href="./bind.html"><tt class="refentry literal"><span class="pre">bind</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="./apply-wrap.html"><tt class="refentry literal"><span class="pre">apply_wrap</span></tt></a></p>
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