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1<?xml version="1.0" encoding="utf-8" ?>
2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
4<head>
5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
6<meta name="generator" content="Docutils 0.3.6: http://docutils.sourceforge.net/" />
7<title>The MPL Reference Manual: front</title>
8<link rel="stylesheet" href="../style.css" type="text/css" />
9</head>
10<body class="docframe refmanual">
11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./erase-key.html" class="navigation-link">Prev</a>&nbsp;<a href="./has-key.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./erase-key.html" class="navigation-link">Back</a>&nbsp;<a href="./has-key.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./intrinsic-metafunctions.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>
12<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./sequences.html" class="navigation-link">Sequences</a> / <a href="./intrinsic-metafunctions.html" class="navigation-link">Intrinsic Metafunctions</a> / <a href="./front.html" class="navigation-link">front</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="front">
15<h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id362" name="front">front</a></h1>
16<div class="section" id="front-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19template&lt;
20      typename Sequence
21    &gt;
22struct <a href="./front.html" class="identifier">front</a>
23{
24    typedef <em>unspecified</em> type;
25};
26</pre>
27</div>
28<div class="section" id="intrinsic-front-description">
29<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
30<p>Returns the first element in the sequence.</p>
31</div>
32<div class="section" id="front-header">
33<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
34<pre class="literal-block">
35#include &lt;<a href="../../../../boost/mpl/front.hpp" class="header">boost/mpl/front.hpp</a>&gt;
36</pre>
37</div>
38<div class="section" id="front-model-of">
39<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3>
40<p><a class="reference" href="./tag-dispatched.html">Tag Dispatched Metafunction</a></p>
41</div>
42<div class="section" id="front-parameters">
43<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
44<table border="1" class="table">
45<colgroup>
46<col width="18%" />
47<col width="27%" />
48<col width="55%" />
49</colgroup>
50<thead valign="bottom">
51<tr><th>Parameter</th>
52<th>Requirement</th>
53<th>Description</th>
54</tr>
55</thead>
56<tbody valign="top">
57<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
58<td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
59<td>A sequence to be examined.</td>
60</tr>
61</tbody>
62</table>
63</div>
64<div class="section" id="intrinsic-front-expression-semantics">
65<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
66<p>For any <a class="reference" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt>:</p>
67<pre class="literal-block">
68typedef <a href="./front.html" class="identifier">front</a>&lt;s&gt;::type t;
69</pre>
70<table class="field-list" frame="void" rules="none">
71<col class="field-name" />
72<col class="field-body" />
73<tbody valign="top">
74<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
75</tr>
76<tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre"><a href="./empty.html" class="identifier">empty</a>&lt;s&gt;::value</span> <span class="pre">==</span> <span class="pre">false</span></tt>.</td>
77</tr>
78<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
79<pre class="last literal-block">
80typedef <a href="./deref.html" class="identifier">deref</a>&lt; <a href="./begin.html" class="identifier">begin</a>&lt;s&gt;::type &gt;::type t;
81</pre>
82</td>
83</tr>
84</tbody>
85</table>
86</div>
87<div class="section" id="front-complexity">
88<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
89<p>Amortized constant time.</p>
90</div>
91<div class="section" id="front-example">
92<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
93<pre class="literal-block">
94typedef <a href="./list.html" class="identifier">list</a>&lt;long&gt;::type types1;
95typedef <a href="./list.html" class="identifier">list</a>&lt;int,long&gt;::type types2;
96typedef <a href="./list.html" class="identifier">list</a>&lt;char,int,long&gt;::type types3;
97
98<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./front.html" class="identifier">front</a>&lt;types1&gt;::type, long &gt; ));
99<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./front.html" class="identifier">front</a>&lt;types2&gt;::type, int&gt; ));
100<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./front.html" class="identifier">front</a>&lt;types3&gt;::type, char&gt; ));
101</pre>
102</div>
103<div class="section" id="intrinsic-front-see-also">
104<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
105<p><a class="reference" href="./forward-sequence.html">Forward Sequence</a>, <a class="refentry reference" href="./back.html"><tt class="refentry literal"><span class="pre">back</span></tt></a>, <a class="refentry reference" href="./push-front.html"><tt class="refentry literal"><span class="pre">push_front</span></tt></a>, <a class="refentry reference" href="./begin.html"><tt class="refentry literal"><span class="pre">begin</span></tt></a>, <a class="refentry reference" href="./deref.html"><tt class="refentry literal"><span class="pre">deref</span></tt></a>, <a class="refentry reference" href="./at.html"><tt class="refentry literal"><span class="pre">at</span></tt></a></p>
106<!-- modtime: November 13, 2004 01:27:55 +0000 -->
107<!-- Sequences/Intrinsic Metafunctions//has_key -->
108</div>
109</div>
110
111<div class="footer-separator"></div>
112<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./erase-key.html" class="navigation-link">Prev</a>&nbsp;<a href="./has-key.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./erase-key.html" class="navigation-link">Back</a>&nbsp;<a href="./has-key.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./intrinsic-metafunctions.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>
113</tr></table></body>
114</html>
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