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7<title>The MPL Reference Manual: reverse_fold</title>
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10<body class="docframe refmanual">
11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./iter-fold.html" class="navigation-link">Prev</a>&nbsp;<a href="./reverse-iter-fold.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./iter-fold.html" class="navigation-link">Back</a>&nbsp;<a href="./reverse-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="./reverse-fold.html" class="navigation-link">reverse_fold</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="reverse-fold">
15<h1><a class="toc-backref" href="./iteration-algorithms.html#id399" name="reverse-fold">reverse_fold</a></h1>
16<div class="section" id="reverse-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 BackwardOp
23    , typename ForwardOp = _1
24    &gt;
25struct <a href="./reverse-fold.html" class="identifier">reverse_fold</a>
26{
27    typedef <em>unspecified</em> type;
28};
29</pre>
30</div>
31<div class="section" id="reverse-description">
32<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
33<p>Returns the result of the successive application of binary <tt class="literal"><span class="pre">BackwardOp</span></tt> to the
34result of the previous <tt class="literal"><span class="pre">BackwardOp</span></tt> invocation (<tt class="literal"><span class="pre">State</span></tt> if it's the first call)
35and every element 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
36reverse order. If <tt class="literal"><span class="pre">ForwardOp</span></tt> is provided, then it is applied on forward
37traversal to form the result that is passed to the first <tt class="literal"><span class="pre">BackwardOp</span></tt> call.</p>
38</div>
39<div class="section" id="reverse-header">
40<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
41<pre class="literal-block">
42#include &lt;<a href="../../../../boost/mpl/reverse_fold.hpp" class="header">boost/mpl/reverse_fold.hpp</a>&gt;
43</pre>
44</div>
45<div class="section" id="reverse-parameters">
46<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
47</div>
48<div class="section" id="iteration-reverse-parameters">
49<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
50<table border="1" class="table">
51<colgroup>
52<col width="16%" />
53<col width="33%" />
54<col width="51%" />
55</colgroup>
56<thead valign="bottom">
57<tr><th>Parameter</th>
58<th>Requirement</th>
59<th>Description</th>
60</tr>
61</thead>
62<tbody valign="top">
63<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
64<td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
65<td>A sequence to iterate.</td>
66</tr>
67<tr><td><tt class="literal"><span class="pre">State</span></tt></td>
68<td>Any type</td>
69<td>The initial state for the first <tt class="literal"><span class="pre">BackwardOp</span></tt>
70/ <tt class="literal"><span class="pre">ForwardOp</span></tt> application.</td>
71</tr>
72<tr><td><tt class="literal"><span class="pre">BackwardOp</span></tt></td>
73<td>Binary <a class="reference" href="./lambda-expression.html">Lambda Expression</a></td>
74<td>The operation to be executed on backward
75traversal.</td>
76</tr>
77<tr><td><tt class="literal"><span class="pre">ForwardOp</span></tt></td>
78<td>Binary <a class="reference" href="./lambda-expression.html">Lambda Expression</a></td>
79<td>The operation to be executed on forward
80traversal.</td>
81</tr>
82</tbody>
83</table>
84</div>
85<div class="section" id="reverse-expression-semantics">
86<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
87<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">backward_op</span></tt> and <tt class="literal"><span class="pre">forward_op</span></tt>,
88and arbitrary type <tt class="literal"><span class="pre">state</span></tt>:</p>
89<pre class="literal-block">
90typedef <a href="./reverse-fold.html" class="identifier">reverse_fold</a>&lt; s,state,backward_op &gt;::type t;
91</pre>
92<table class="field-list" frame="void" rules="none">
93<col class="field-name" />
94<col class="field-body" />
95<tbody valign="top">
96<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type</td>
97</tr>
98<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
99<pre class="last literal-block">
100typedef <a href="./reverse-iter-fold.html" class="identifier">reverse_iter_fold</a>&lt; 
101      s
102    , state
103    , <a href="./apply.html" class="identifier">apply</a>&lt;backward_op,_1,<a href="./deref.html" class="identifier">deref</a>&lt;_2&gt; &gt;
104    &gt;::type t;
105</pre>
106</td>
107</tr>
108</tbody>
109</table>
110<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
111<pre class="literal-block">
112typedef <a href="./reverse-fold.html" class="identifier">reverse_fold</a>&lt; s,state,backward_op,forward_op &gt;::type t;
113</pre>
114<table class="field-list" frame="void" rules="none">
115<col class="field-name" />
116<col class="field-body" />
117<tbody valign="top">
118<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
119</tr>
120<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
121<pre class="last literal-block">
122typedef <a href="./reverse-fold.html" class="identifier">reverse_fold</a>&lt;
123      Sequence
124    , <a href="./fold.html" class="identifier">fold</a>&lt;s,state,forward_op&gt;::type
125    , backward_op
126    &gt;::type t;       
127</pre>
128</td>
129</tr>
130</tbody>
131</table>
132</div>
133<div class="section" id="reverse-complexity">
134<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
135<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">backward_op</span></tt> and <tt class="literal"><span class="pre">forward_op</span></tt>.</p>
136</div>
137<div class="section" id="reverse-example">
138<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
139<p>Remove negative elements from a sequence <a class="footnote-reference" href="#reverse-fold-note" id="id93" name="id93">[2]</a>.</p>
140<pre class="literal-block">
141typedef <a href="./list-c.html" class="identifier">list_c</a>&lt;int,5,-1,0,-7,-2,0,-5,4&gt; numbers;
142typedef <a href="./list-c.html" class="identifier">list_c</a>&lt;int,-1,-7,-2,-5&gt; negatives;
143typedef <a href="./reverse-fold.html" class="identifier">reverse_fold</a>&lt;
144      numbers
145    , <a href="./list-c.html" class="identifier">list_c</a>&lt;int&gt;
146    , <a href="./if.html" class="identifier">if_</a>&lt; <a href="./less.html" class="identifier">less</a>&lt; _2,<a href="./int.html" class="identifier">int_</a>&lt;0&gt; &gt;, <a href="./push-front.html" class="identifier">push_front</a>&lt;_1,_2,&gt;, _1 &gt;
147    &gt;::type result;
148
149<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./equal.html" class="identifier">equal</a>&lt; negatives,result > ));
150</pre>
151<table class="footnote" frame="void" id="reverse-fold-note" rules="none">
152<colgroup><col class="label" /><col /></colgroup>
153<tbody valign="top">
154<tr><td class="label"><a class="fn-backref" href="#id93" name="reverse-fold-note">[2]</a></td><td>See <tt class="literal"><span class="pre"><a href="./remove-if.html" class="identifier">remove_if</a></span></tt> for a more compact way to do this.</td></tr>
155</tbody>
156</table>
157</div>
158<div class="section" id="reverse-see-also">
159<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
160<p><a class="reference" href="./algorithms.html">Algorithms</a>, <a class="refentry reference" href="./fold.html"><tt class="refentry literal"><span class="pre">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="./iter-fold.html"><tt class="refentry literal"><span class="pre">iter_fold</span></tt></a></p>
161<!-- modtime: November 13, 2004 18:32:22 +0000 -->
162<!-- Algorithms/Iteration Algorithms//reverse_iter_fold -->
163</div>
164</div>
165
166<div class="footer-separator"></div>
167<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./iter-fold.html" class="navigation-link">Prev</a>&nbsp;<a href="./reverse-iter-fold.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./iter-fold.html" class="navigation-link">Back</a>&nbsp;<a href="./reverse-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>
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