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- <h1 class="title">Bidirectional Traversal Concept</h1>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <p>A class or built-in type <tt class="docutils literal"><span class="pre">X</span></tt> models the <em>Bidirectional Traversal</em>
- concept if, in addition to <tt class="docutils literal"><span class="pre">X</span></tt> meeting the requirements of Forward
- Traversal Iterator, the following expressions are valid and respect
- the stated semantics.</p>
- <table border="1" class="docutils">
- <colgroup>
- <col width="38%" />
- <col width="37%" />
- <col width="25%" />
- </colgroup>
- <thead valign="bottom">
- <tr><th class="head" colspan="3">Bidirectional Traversal Iterator Requirements (in addition to Forward Traversal
- Iterator)</th>
- </tr>
- <tr><th class="head">Expression</th>
- <th class="head">Return Type</th>
- <th class="head">Assertion/Semantics /
- Pre-/Post-condition</th>
- </tr>
- </thead>
- <tbody valign="top">
- <tr><td><tt class="docutils literal"><span class="pre">--r</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">X&</span></tt></td>
- <td>pre: there exists
- <tt class="docutils literal"><span class="pre">s</span></tt> such that <tt class="docutils literal"><span class="pre">r</span>
- <span class="pre">==</span> <span class="pre">++s</span></tt>. post:
- <tt class="docutils literal"><span class="pre">s</span></tt> is
- dereferenceable.
- <tt class="docutils literal"><span class="pre">--(++r)</span> <span class="pre">==</span> <span class="pre">r</span></tt>.
- <tt class="docutils literal"><span class="pre">--r</span> <span class="pre">==</span> <span class="pre">--s</span></tt>
- implies <tt class="docutils literal"><span class="pre">r</span> <span class="pre">==</span>
- <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>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">r--</span></tt></td>
- <td>convertible to <tt class="docutils literal"><span class="pre">const</span> <span class="pre">X&</span></tt></td>
- <td><pre class="first last literal-block">
- {
- X tmp = r;
- --r;
- return tmp;
- }
- </pre>
- </td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">iterator_traversal<X>::type</span></tt></td>
- <td>Convertible to
- <tt class="docutils literal"><span class="pre">bidirectional_traversal_tag</span></tt></td>
- <td> </td>
- </tr>
- </tbody>
- </table>
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