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7 <title>The MPL Reference Manual: protect
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14 <div class=
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"protect">
15 <h1><a class=
"toc-backref" href=
"./composition-and-argument-binding.html#id1534">protect
</a></h1>
16 <div class=
"section" id=
"id953">
17 <h3><a class=
"subsection-title" href=
"#synopsis" name=
"synopsis">Synopsis
</a></h3>
18 <pre class=
"literal-block">
22 struct
<a href=
"./protect.html" class=
"identifier">protect
</a>
24 //
<em>unspecified
</em>
29 <div class=
"section" id=
"id954">
30 <h3><a class=
"subsection-title" href=
"#description" name=
"description">Description
</a></h3>
31 <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
32 its argument from being recognized as a
<a class=
"reference internal" href=
"./terminology.html#bind-expression">bind expression
</a>.
</p>
34 <div class=
"section" id=
"id955">
35 <h3><a class=
"subsection-title" href=
"#header" name=
"header">Header
</a></h3>
36 <pre class=
"literal-block">
37 #include
<<a href=
"../../../../boost/mpl/protect.hpp" class=
"header">boost/mpl/protect.hpp
</a>>
40 <div class=
"section" id=
"id956">
41 <h3><a class=
"subsection-title" href=
"#parameters" name=
"parameters">Parameters
</a></h3>
42 <table border=
"1" class=
"docutils table">
48 <thead valign=
"bottom">
49 <tr><th class=
"head">Parameter
</th>
50 <th class=
"head">Requirement
</th>
51 <th class=
"head">Description
</th>
55 <tr><td><tt class=
"literal"><span class=
"pre">F
</span></tt></td>
56 <td><a class=
"reference internal" href=
"./metafunction-class.html">Metafunction Class
</a></td>
57 <td>A metafunction class to wrap.
</td>
62 <div class=
"section" id=
"id957">
63 <h3><a class=
"subsection-title" href=
"#expression-semantics" name=
"expression-semantics">Expression semantics
</a></h3>
64 <p>For any
<a class=
"reference internal" href=
"./metafunction-class.html">Metafunction Class
</a> <tt class=
"literal"><span class=
"pre">f
</span></tt>:
</p>
65 <pre class=
"literal-block">
66 typedef
<a href=
"./protect.html" class=
"identifier">protect
</a><f
> g;
68 <table class=
"docutils field-list" frame=
"void" rules=
"none">
69 <col class=
"field-name" />
70 <col class=
"field-body" />
72 <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>
75 <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>
76 <pre class=
"literal-block">
80 typename U1 =
<em>unspecified
</em>,
<em>...
</em> typename U
<em>n
</em> =
<em>unspecified
</em>
82 struct
<a href=
"./apply.html" class=
"identifier">apply
</a>
83 :
<a href=
"./apply-wrap.html" class=
"identifier">apply_wrap
</a><em>n
</em><f,U1,
<em>...
</em>U
<em>n
</em>>
88 <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>
94 <div class=
"section" id=
"id958">
95 <h3><a class=
"subsection-title" href=
"#example" name=
"example">Example
</a></h3>
96 <pre class=
"literal-block">
99 template
< typename T1, typename T2
> struct
<a href=
"./apply.html" class=
"identifier">apply
</a>
105 typedef
<a href=
"./bind.html" class=
"identifier">bind
</a>< <a href=
"./quote.html" class=
"identifier">quote
</a><tt class=
"literal"><span class=
"pre">3</span></tt><<a href=
"./if.html" class=
"identifier">if_
</a>>,
<a href=
"./placeholders.html" class=
"identifier">_1
</a>,
<a href=
"./placeholders.html" class=
"identifier">_2
</a>,
<a href=
"./bind.html" class=
"identifier">bind
</a><f,
<a href=
"./placeholders.html" class=
"identifier">_1
</a>,
<a href=
"./placeholders.html" class=
"identifier">_2
</a>> > b1;
106 typedef
<a href=
"./bind.html" class=
"identifier">bind
</a>< <a href=
"./quote.html" class=
"identifier">quote
</a><tt class=
"literal"><span class=
"pre">3</span></tt><<a href=
"./if.html" class=
"identifier">if_
</a>>,
<a href=
"./placeholders.html" class=
"identifier">_1
</a>,
<a href=
"./placeholders.html" class=
"identifier">_2
</a>,
<a href=
"./protect.html" class=
"identifier">protect
</a>< <a href=
"./bind.html" class=
"identifier">bind
</a><f,
<a href=
"./placeholders.html" class=
"identifier">_1
</a>,
<a href=
"./placeholders.html" class=
"identifier">_2
</a>> > > b2;
108 typedef
<a href=
"./apply-wrap.html" class=
"identifier">apply_wrap
</a><tt class=
"literal"><span class=
"pre">2</span></tt>< b1,
<a href=
"./bool.html" class=
"identifier">false_
</a>,char
>::type r1;
109 typedef
<a href=
"./apply-wrap.html" class=
"identifier">apply_wrap
</a><tt class=
"literal"><span class=
"pre">2</span></tt>< b2,
<a href=
"./bool.html" class=
"identifier">false_
</a>,char
>::type r2;
111 <a href=
"./assert.html" class=
"identifier">BOOST_MPL_ASSERT
</a>(( is_same
<r1,char
> ));
112 <a href=
"./assert.html" class=
"identifier">BOOST_MPL_ASSERT
</a>(( is_same
<r2,
<a href=
"./protect.html" class=
"identifier">protect
</a>< <a href=
"./bind.html" class=
"identifier">bind
</a><f,
<a href=
"./placeholders.html" class=
"identifier">_1
</a>,
<a href=
"./placeholders.html" class=
"identifier">_2
</a>> > > ));
115 <div class=
"section" id=
"id959">
116 <h3><a class=
"subsection-title" href=
"#see-also" name=
"see-also">See also
</a></h3>
117 <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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123 <td><div class=
"copyright-footer"><div class=
"copyright">Copyright ©
2001-
2009 Aleksey Gurtovoy and David Abrahams
</div>
124 Distributed under the Boost Software License, Version
1.0. (See accompanying
125 file LICENSE_1_0.txt or copy at
<a class=
"reference external" href=
"http://www.boost.org/LICENSE_1_0.txt" target=
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