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7<title>The MPL Reference Manual: fold</title>
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11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./iteration-algorithms.html" class="navigation-link">Prev</a>&nbsp;<a href="./iter-fold.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group">Back&nbsp;<a href="./iter-fold.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./iteration-algorithms.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="./algorithms.html" class="navigation-link">Algorithms</a> / <a href="./iteration-algorithms.html" class="navigation-link">Iteration Algorithms</a> / <a href="./fold.html" class="navigation-link">fold</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="fold">
15<h1><a class="toc-backref" href="./iteration-algorithms.html#id397" name="fold">fold</a></h1>
16<div class="section" id="fold-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    , typename State
22    , typename ForwardOp
23    &gt;
24struct <a href="./fold.html" class="identifier">fold</a>
25{
26    typedef <em>unspecified</em> type;
27};
28</pre>
29</div>
30<div class="section" id="fold-description">
31<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
32<p>Returns the result of the successive application of binary <tt class="literal"><span class="pre">ForwardOp</span></tt> to the
33result of the previous <tt class="literal"><span class="pre">ForwardOp</span></tt> invocation (<tt class="literal"><span class="pre">State</span></tt> if it's the first call)
34and every element of the sequence in the range [<tt class="literal"><span class="pre"><a href="./begin.html" class="identifier">begin</a>&lt;Sequence&gt;::type</span></tt>, <tt class="literal"><span class="pre"><a href="./end.html" class="identifier">end</a>&lt;Sequence&gt;::type</span></tt>) in order.</p>
35</div>
36<div class="section" id="fold-header">
37<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
38<pre class="literal-block">
39#include &lt;<a href="../../../../boost/mpl/fold.hpp" class="header">boost/mpl/fold.hpp</a>&gt;
40</pre>
41</div>
42<div class="section" id="fold-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="15%" />
47<col width="32%" />
48<col width="53%" />
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 iterate.</td>
60</tr>
61<tr><td><tt class="literal"><span class="pre">State</span></tt></td>
62<td>Any type</td>
63<td>The initial state for the first <tt class="literal"><span class="pre">ForwardOp</span></tt>
64application.</td>
65</tr>
66<tr><td><tt class="literal"><span class="pre">ForwardOp</span></tt></td>
67<td>Binary <a class="reference" href="./lambda-expression.html">Lambda Expression</a></td>
68<td>The operation to be executed on forward
69traversal.</td>
70</tr>
71</tbody>
72</table>
73</div>
74<div class="section" id="fold-expression-semantics">
75<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
76<p>For any <a class="reference" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt>, binary <a class="reference" href="./lambda-expression.html">Lambda Expression</a> <tt class="literal"><span class="pre">op</span></tt>, and arbitrary type <tt class="literal"><span class="pre">state</span></tt>:</p>
77<pre class="literal-block">
78typedef <a href="./fold.html" class="identifier">fold</a>&lt;s,state,op&gt;::type t;
79</pre>
80<table class="field-list" frame="void" rules="none">
81<col class="field-name" />
82<col class="field-body" />
83<tbody valign="top">
84<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
85</tr>
86<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
87<pre class="last literal-block">
88typedef <a href="./iter-fold.html" class="identifier">iter_fold</a>&lt; s,state,<a href="./apply.html" class="identifier">apply</a>&lt;op,_1,<a href="./deref.html" class="identifier">deref</a>&lt;_2&gt; &gt; &gt;::type t;
89</pre>
90</td>
91</tr>
92</tbody>
93</table>
94</div>
95<div class="section" id="fold-complexity">
96<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
97<p>Linear. Exactly <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a>&lt;s&gt;::value</span></tt> applications of <tt class="literal"><span class="pre">op</span></tt>.</p>
98</div>
99<div class="section" id="fold-example">
100<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
101<pre class="literal-block">
102typedef <a href="./vector.html" class="identifier">vector</a>&lt;long,float,short,double,float,long,long double&gt; types;
103typedef <a href="./fold.html" class="identifier">fold</a>&lt;
104      types
105    , <a href="./int.html" class="identifier">int_</a>&lt;0&gt;
106    , <a href="./if.html" class="identifier">if_</a>&lt; is_float&lt;_2&gt;,<a href="./next.html" class="identifier">next</a>&lt;_1&gt;,_1 &gt;
107    &gt;::type number_of_floats;
108
109<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( number_of_floats::value, ==, 4 );
110</pre>
111</div>
112<div class="section" id="fold-see-also">
113<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
114<p><a class="reference" href="./algorithms.html">Algorithms</a>, <a class="refentry reference" href="./accumulate.html"><tt class="refentry literal"><span class="pre">accumulate</span></tt></a>, <a class="refentry reference" href="./reverse-fold.html"><tt class="refentry literal"><span class="pre">reverse_fold</span></tt></a>, <a class="refentry reference" href="./iter-fold.html"><tt class="refentry literal"><span class="pre">iter_fold</span></tt></a>, <a class="refentry reference" href="./reverse-iter-fold.html"><tt class="refentry literal"><span class="pre">reverse_iter_fold</span></tt></a>, <a class="refentry reference" href="./copy.html"><tt class="refentry literal"><span class="pre">copy</span></tt></a>, <a class="refentry reference" href="./copy-if.html"><tt class="refentry literal"><span class="pre">copy_if</span></tt></a></p>
115<!-- modtime: November 10, 2004 04:46:33 +0000 -->
116<!-- Algorithms/Iteration Algorithms//iter_fold -->
117</div>
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