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10<title>The MPL Reference Manual: reverse_fold</title>
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13<body class="docframe refmanual">
14<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>
15<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>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="reverse-fold">
18<h1><a class="toc-backref" href="./iteration-algorithms.html#id399" name="reverse-fold">reverse_fold</a></h1>
19<div class="section" id="reverse-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22template&lt;
23      typename Sequence
24    , typename State
25    , typename BackwardOp
26    , typename ForwardOp = _1
27    &gt;
28struct <a href="./reverse-fold.html" class="identifier">reverse_fold</a>
29{
30    typedef <em>unspecified</em> type;
31};
32</pre>
33</div>
34<div class="section" id="reverse-description">
35<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
36<p>Returns the result of the successive application of binary <tt class="literal"><span class="pre">BackwardOp</span></tt> to the
37result 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)
38and 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
39reverse order. If <tt class="literal"><span class="pre">ForwardOp</span></tt> is provided, then it is applied on forward
40traversal to form the result that is passed to the first <tt class="literal"><span class="pre">BackwardOp</span></tt> call.</p>
41</div>
42<div class="section" id="reverse-header">
43<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
44<pre class="literal-block">
45#include &lt;<a href="../../../../boost/mpl/reverse_fold.hpp" class="header">boost/mpl/reverse_fold.hpp</a>&gt;
46</pre>
47</div>
48<div class="section" id="reverse-parameters">
49<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
50</div>
51<div class="section" id="iteration-reverse-parameters">
52<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
53<table border="1" class="table">
54<colgroup>
55<col width="16%" />
56<col width="33%" />
57<col width="51%" />
58</colgroup>
59<thead valign="bottom">
60<tr><th>Parameter</th>
61<th>Requirement</th>
62<th>Description</th>
63</tr>
64</thead>
65<tbody valign="top">
66<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
67<td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
68<td>A sequence to iterate.</td>
69</tr>
70<tr><td><tt class="literal"><span class="pre">State</span></tt></td>
71<td>Any type</td>
72<td>The initial state for the first <tt class="literal"><span class="pre">BackwardOp</span></tt>
73/ <tt class="literal"><span class="pre">ForwardOp</span></tt> application.</td>
74</tr>
75<tr><td><tt class="literal"><span class="pre">BackwardOp</span></tt></td>
76<td>Binary <a class="reference" href="./lambda-expression.html">Lambda Expression</a></td>
77<td>The operation to be executed on backward
78traversal.</td>
79</tr>
80<tr><td><tt class="literal"><span class="pre">ForwardOp</span></tt></td>
81<td>Binary <a class="reference" href="./lambda-expression.html">Lambda Expression</a></td>
82<td>The operation to be executed on forward
83traversal.</td>
84</tr>
85</tbody>
86</table>
87</div>
88<div class="section" id="reverse-expression-semantics">
89<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
90<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>,
91and arbitrary type <tt class="literal"><span class="pre">state</span></tt>:</p>
92<pre class="literal-block">
93typedef <a href="./reverse-fold.html" class="identifier">reverse_fold</a>&lt; s,state,backward_op &gt;::type t;
94</pre>
95<table class="field-list" frame="void" rules="none">
96<col class="field-name" />
97<col class="field-body" />
98<tbody valign="top">
99<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type</td>
100</tr>
101<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
102<pre class="last literal-block">
103typedef <a href="./reverse-iter-fold.html" class="identifier">reverse_iter_fold</a>&lt; 
104      s
105    , state
106    , <a href="./apply.html" class="identifier">apply</a>&lt;backward_op,_1,<a href="./deref.html" class="identifier">deref</a>&lt;_2&gt; &gt;
107    &gt;::type t;
108</pre>
109</td>
110</tr>
111</tbody>
112</table>
113<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
114<pre class="literal-block">
115typedef <a href="./reverse-fold.html" class="identifier">reverse_fold</a>&lt; s,state,backward_op,forward_op &gt;::type t;
116</pre>
117<table class="field-list" frame="void" rules="none">
118<col class="field-name" />
119<col class="field-body" />
120<tbody valign="top">
121<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
122</tr>
123<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
124<pre class="last literal-block">
125typedef <a href="./reverse-fold.html" class="identifier">reverse_fold</a>&lt;
126      Sequence
127    , <a href="./fold.html" class="identifier">fold</a>&lt;s,state,forward_op&gt;::type
128    , backward_op
129    &gt;::type t;       
130</pre>
131</td>
132</tr>
133</tbody>
134</table>
135</div>
136<div class="section" id="reverse-complexity">
137<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
138<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>
139</div>
140<div class="section" id="reverse-example">
141<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
142<p>Remove negative elements from a sequence <a class="footnote-reference" href="#reverse-fold-note" id="id93" name="id93">[2]</a>.</p>
143<pre class="literal-block">
144typedef <a href="./list-c.html" class="identifier">list_c</a>&lt;int,5,-1,0,-7,-2,0,-5,4&gt; numbers;
145typedef <a href="./list-c.html" class="identifier">list_c</a>&lt;int,-1,-7,-2,-5&gt; negatives;
146typedef <a href="./reverse-fold.html" class="identifier">reverse_fold</a>&lt;
147      numbers
148    , <a href="./list-c.html" class="identifier">list_c</a>&lt;int&gt;
149    , <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;
150    &gt;::type result;
151
152<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./equal.html" class="identifier">equal</a>&lt; negatives,result > ));
153</pre>
154<table class="footnote" frame="void" id="reverse-fold-note" rules="none">
155<colgroup><col class="label" /><col /></colgroup>
156<tbody valign="top">
157<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>
158</tbody>
159</table>
160</div>
161<div class="section" id="reverse-see-also">
162<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
163<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>
164<!-- modtime: November 13, 2004 18:32:22 +0000 -->
165<!-- Algorithms/Iteration Algorithms//reverse_iter_fold -->
166</div>
167</div>
168
169<div class="footer-separator"></div>
170<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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