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7 <title>The MPL Reference Manual: front
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12 <td class=
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14 <div class=
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15 <h1><a class=
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"./intrinsic-metafunctions.html#id1434">front
</a></h1>
16 <div class=
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17 <h3><a class=
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"#synopsis" name=
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18 <pre class=
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22 struct
<a href=
"./front.html" class=
"identifier">front
</a>
24 typedef
<em>unspecified
</em> type;
28 <div class=
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"id257">
29 <h3><a class=
"subsection-title" href=
"#description" name=
"description">Description
</a></h3>
30 <p>Returns the first element in the sequence.
</p>
32 <div class=
"section" id=
"id258">
33 <h3><a class=
"subsection-title" href=
"#header" name=
"header">Header
</a></h3>
34 <pre class=
"literal-block">
35 #include
<<a href=
"../../../../boost/mpl/front.hpp" class=
"header">boost/mpl/front.hpp
</a>>
38 <div class=
"section" id=
"id259">
39 <h3><a class=
"subsection-title" href=
"#model-of" name=
"model-of">Model of
</a></h3>
40 <p><a class=
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"./tag-dispatched-metafunction.html">Tag Dispatched Metafunction
</a></p>
42 <div class=
"section" id=
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43 <h3><a class=
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"#parameters" name=
"parameters">Parameters
</a></h3>
44 <table border=
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50 <thead valign=
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51 <tr><th class=
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52 <th class=
"head">Requirement
</th>
53 <th class=
"head">Description
</th>
57 <tr><td><tt class=
"literal"><span class=
"pre">Sequence
</span></tt></td>
58 <td><a class=
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</a></td>
59 <td>A sequence to be examined.
</td>
64 <div class=
"section" id=
"id261">
65 <h3><a class=
"subsection-title" href=
"#expression-semantics" name=
"expression-semantics">Expression semantics
</a></h3>
66 <p>For any
<a class=
"reference internal" href=
"./forward-sequence.html">Forward Sequence
</a> <tt class=
"literal"><span class=
"pre">s
</span></tt>:
</p>
67 <pre class=
"literal-block">
68 typedef
<a href=
"./front.html" class=
"identifier">front
</a><s
>::type t;
70 <table class=
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71 <col class=
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72 <col class=
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74 <tr class=
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</p>
77 <tr class=
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</th><td class=
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"first"><tt class=
"literal"><span class=
"pre"><a href=
"./empty.html" class=
"identifier">empty
</a><s
>::value
</span> <span class=
"pre">==
</span> <span class=
"pre">false
</span></tt>.
</p>
80 <tr class=
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"field-name">Semantics:
</th><td class=
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</p>
81 <pre class=
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82 typedef
<a href=
"./deref.html" class=
"identifier">deref
</a>< <a href=
"./begin.html" class=
"identifier">begin
</a><s
>::type
>::type t;
89 <div class=
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"id262">
90 <h3><a class=
"subsection-title" href=
"#complexity" name=
"complexity">Complexity
</a></h3>
91 <p>Amortized constant time.
</p>
93 <div class=
"section" id=
"id263">
94 <h3><a class=
"subsection-title" href=
"#example" name=
"example">Example
</a></h3>
95 <pre class=
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96 typedef
<a href=
"./list.html" class=
"identifier">list
</a><long
>::type types1;
97 typedef
<a href=
"./list.html" class=
"identifier">list
</a><int,long
>::type types2;
98 typedef
<a href=
"./list.html" class=
"identifier">list
</a><char,int,long
>::type types3;
100 <a href=
"./assert.html" class=
"identifier">BOOST_MPL_ASSERT
</a>(( is_same
< <a href=
"./front.html" class=
"identifier">front
</a><types1
>::type, long
> ));
101 <a href=
"./assert.html" class=
"identifier">BOOST_MPL_ASSERT
</a>(( is_same
< <a href=
"./front.html" class=
"identifier">front
</a><types2
>::type, int
> ));
102 <a href=
"./assert.html" class=
"identifier">BOOST_MPL_ASSERT
</a>(( is_same
< <a href=
"./front.html" class=
"identifier">front
</a><types3
>::type, char
> ));
105 <div class=
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106 <h3><a class=
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"#see-also" name=
"see-also">See also
</a></h3>
107 <p><a class=
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"./forward-sequence.html">Forward Sequence
</a>,
<a class=
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108 <!-- Sequences/Intrinsic Metafunctions//has_key -->
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114 <td><div class=
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2001-
2009 Aleksey Gurtovoy and David Abrahams
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115 Distributed under the Boost Software License, Version
1.0. (See accompanying
116 file LICENSE_1_0.txt or copy at
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