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3.4 KiB
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<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
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<title>Bidirectional Traversal Concept</title>
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<link rel="stylesheet" href="../../../rst.css" type="text/css" />
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</head>
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<div class="document" id="bidirectional-traversal-concept">
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<h1 class="title">Bidirectional Traversal Concept</h1>
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
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<!-- Software License, Version 1.0. (See accompanying -->
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<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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<p>A class or built-in type <tt class="docutils literal"><span class="pre">X</span></tt> models the <em>Bidirectional Traversal</em>
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concept if, in addition to <tt class="docutils literal"><span class="pre">X</span></tt> meeting the requirements of Forward
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Traversal Iterator, the following expressions are valid and respect
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the stated semantics.</p>
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<table border="1" class="docutils">
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<colgroup>
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<col width="38%" />
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<col width="37%" />
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<col width="25%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th class="head" colspan="3">Bidirectional Traversal Iterator Requirements (in addition to Forward Traversal
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Iterator)</th>
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</tr>
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<tr><th class="head">Expression</th>
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<th class="head">Return Type</th>
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<th class="head">Assertion/Semantics /
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Pre-/Post-condition</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr><td><tt class="docutils literal"><span class="pre">--r</span></tt></td>
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<td><tt class="docutils literal"><span class="pre">X&</span></tt></td>
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<td>pre: there exists
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<tt class="docutils literal"><span class="pre">s</span></tt> such that <tt class="docutils literal"><span class="pre">r</span>
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<span class="pre">==</span> <span class="pre">++s</span></tt>. post:
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<tt class="docutils literal"><span class="pre">s</span></tt> is
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dereferenceable.
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<tt class="docutils literal"><span class="pre">--(++r)</span> <span class="pre">==</span> <span class="pre">r</span></tt>.
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<tt class="docutils literal"><span class="pre">--r</span> <span class="pre">==</span> <span class="pre">--s</span></tt>
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implies <tt class="docutils literal"><span class="pre">r</span> <span class="pre">==</span>
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<span class="pre">s</span></tt>. <tt class="docutils literal"><span class="pre">&r</span> <span class="pre">==</span> <span class="pre">&--r</span></tt>.</td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">r--</span></tt></td>
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<td>convertible to <tt class="docutils literal"><span class="pre">const</span> <span class="pre">X&</span></tt></td>
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<td><pre class="first last literal-block">
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{
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X tmp = r;
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--r;
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return tmp;
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}
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</pre>
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</td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">iterator_traversal<X>::type</span></tt></td>
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<td>Convertible to
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<tt class="docutils literal"><span class="pre">bidirectional_traversal_tag</span></tt></td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</div>
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<a class="reference external" href="BidirectionalTraversal.rst">View document source</a>.
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