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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-binding.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-binding.html#id1534">protect</a></h1>
<div class="section" id="id953">
<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="id954">
<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 internal" href="./metafunction-class.html">Metafunction Class</a> that prevents
its argument from being recognized as a <a class="reference internal" href="./terminology.html#bind-expression">bind expression</a>.</p>
</div>
<div class="section" id="id955">
<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>
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<div class="section" id="id956">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<col width="19%" />
<col width="33%" />
<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 wrap.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id957">
<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>:</p>
<pre class="literal-block">
typedef <a href="./protect.html" class="identifier">protect</a>&lt;f&gt; g;
</pre>
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<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>.</p>
</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 internal" 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>
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<div class="section" id="id958">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
struct f
{
    template&lt; typename T1, typename T2 &gt; struct <a href="./apply.html" class="identifier">apply</a>
    {
        typedef T2 type;
    };
};

typedef <a href="./bind.html" class="identifier">bind</a>&lt; <a href="./quote.html" class="identifier">quote</a><tt class="literal"><span class="pre">3</span></tt>&lt;<a href="./if.html" class="identifier">if_</a>&gt;,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>,<a href="./bind.html" class="identifier">bind</a>&lt;f,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>&gt; &gt; b1;
typedef <a href="./bind.html" class="identifier">bind</a>&lt; <a href="./quote.html" class="identifier">quote</a><tt class="literal"><span class="pre">3</span></tt>&lt;<a href="./if.html" class="identifier">if_</a>&gt;,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>,<a href="./protect.html" class="identifier">protect</a>&lt; <a href="./bind.html" class="identifier">bind</a>&lt;f,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>&gt; &gt; &gt; b2;

typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">2</span></tt>&lt; b1,<a href="./bool.html" class="identifier">false_</a>,char &gt;::type r1;
typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">2</span></tt>&lt; b2,<a href="./bool.html" class="identifier">false_</a>,char &gt;::type r2;

<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,<a href="./protect.html" class="identifier">protect</a>&lt; <a href="./bind.html" class="identifier">bind</a>&lt;f,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>&gt; > > ));
</pre>
</div>
<div class="section" id="id959">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference internal" href="./composition-and-argument-binding.html">Composition and Argument Binding</a>, <a class="reference internal" href="./invocation.html">invocation</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./quote.html">quote</a>, <a class="reference internal" href="./apply-wrap.html">apply_wrap</a></p>
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