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10<title>The MPL Reference Manual: reverse_iter_fold</title>
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14<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./reverse-fold.html" class="navigation-link">Prev</a>&nbsp;<a href="./accumulate.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./reverse-fold.html" class="navigation-link">Back</a>&nbsp;<a href="./accumulate.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-iter-fold.html" class="navigation-link">reverse_iter_fold</a></td>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="reverse-iter-fold">
18<h1><a class="toc-backref" href="./iteration-algorithms.html#id400" name="reverse-iter-fold">reverse_iter_fold</a></h1>
19<div class="section" id="iteration-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-iter-fold.html" class="identifier">reverse_iter_fold</a>
29{
30    typedef <em>unspecified</em>  type;
31};
32</pre>
33</div>
34<div class="section" id="iteration-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 each iterator 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>)
39in reverse order. If <tt class="literal"><span class="pre">ForwardOp</span></tt> is provided, then it's applied on forward
40traversal to form the result which is passed to the first <tt class="literal"><span class="pre">BackwardOp</span></tt> call.</p>
41</div>
42<div class="section" id="iteration-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_iter_fold.hpp" class="header">boost/mpl/reverse_iter_fold.hpp</a>&gt;
46</pre>
47</div>
48<div class="section" id="algorithms-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="iteration-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-iter-fold.html" class="identifier">reverse_iter_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="literal-block">
100typedef <a href="./begin.html" class="identifier">begin</a>&lt;s&gt;::type i<sub>1</sub>;
101typedef <a href="./next.html" class="identifier">next</a>&lt;i<sub>1</sub>&gt;::type i<sub>2</sub>;
102<em>...</em>
103typedef <a href="./next.html" class="identifier">next</a>&lt;i<sub>n</sub>&gt;::type last;
104typedef <a href="./apply.html" class="identifier">apply</a>&lt;backward_op,state,i<sub>n</sub>&gt;::type state<sub>n</sub>;
105typedef <a href="./apply.html" class="identifier">apply</a>&lt;backward_op,state<sub>n</sub>,i<sub>n-1</sub>&gt;::type state<sub>n-1</sub>;
106<em>...</em>
107typedef <a href="./apply.html" class="identifier">apply</a>&lt;backward_op,state<sub>2</sub>,i<sub>1</sub>&gt;::type state<sub>1</sub>;
108typedef state<sub>1</sub> t;
109</pre>
110<p class="last">where <tt class="literal"><span class="pre">n</span> <span class="pre">==</span> <span class="pre"><a href="./size.html" class="identifier">size</a>&lt;s&gt;::value</span></tt> and <tt class="literal"><span class="pre">last</span></tt> is identical to <tt class="literal"><span class="pre"><a href="./end.html" class="identifier">end</a>&lt;s&gt;::type</span></tt>; equivalent
111to <tt class="literal"><span class="pre">typedef</span> <span class="pre">state</span> <span class="pre">t;</span></tt> if <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">true</span></tt>.</p>
112</td>
113</tr>
114</tbody>
115</table>
116<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
117<pre class="literal-block">
118typedef <a href="./reverse-iter-fold.html" class="identifier">reverse_iter_fold</a>&lt; s,state,backward_op,forward_op &gt;::type t;
119</pre>
120<table class="field-list" frame="void" rules="none">
121<col class="field-name" />
122<col class="field-body" />
123<tbody valign="top">
124<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
125</tr>
126<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
127<pre class="last literal-block">
128typedef <a href="./reverse-iter-fold.html" class="identifier">reverse_iter_fold</a>&lt;
129      Sequence
130    , <a href="./iter-fold.html" class="identifier">iter_fold</a>&lt;s,state,forward_op&gt;::type
131    , backward_op
132    &gt;::type t;
133</pre>
134</td>
135</tr>
136</tbody>
137</table>
138</div>
139<div class="section" id="iteration-reverse-complexity">
140<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
141<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>
142</div>
143<div class="section" id="iteration-reverse-example">
144<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
145<p>Build a list of iterators to the negative elements in a sequence.</p>
146<pre class="literal-block">
147typedef <a href="./vector-c.html" class="identifier">vector_c</a>&lt;int,5,-1,0,-7,-2,0,-5,4&gt; numbers;
148typedef <a href="./list-c.html" class="identifier">list_c</a>&lt;int,-1,-7,-2,-5&gt; negatives;
149typedef <a href="./reverse-iter-fold.html" class="identifier">reverse_iter_fold</a>&lt;
150      numbers
151    , <a href="./list.html" class="identifier">list</a>&lt;&gt;
152    , <a href="./if.html" class="identifier">if_</a>&lt; <a href="./less.html" class="identifier">less</a>&lt; <a href="./deref.html" class="identifier">deref</a>&lt;_2&gt;,<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;
153    &gt;::type iters;
154
155<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./equal.html" class="identifier">equal</a>&lt; 
156      negatives
157    , <a href="./transform-view.html" class="identifier">transform_view</a>&lt; iters,<a href="./deref.html" class="identifier">deref</a>&lt;_1&gt; >
158    > ));
159</pre>
160</div>
161<div class="section" id="iteration-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="./iter-fold.html"><tt class="refentry literal"><span class="pre">iter_fold</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="./fold.html"><tt class="refentry literal"><span class="pre">fold</span></tt></a></p>
164<!-- modtime: November 13, 2004 02:51:20 +0000 -->
165<!-- Algorithms/Iteration Algorithms//accumulate |10 -->
166</div>
167</div>
168
169<div class="footer-separator"></div>
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