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| <div class="document" id="bidirectional-traversal-concept"> |
| <h1 class="title">Bidirectional Traversal Concept</h1> |
| |
| <!-- Copyright David Abrahams 2006. Distributed under the Boost --> |
| <!-- Software License, Version 1.0. (See accompanying --> |
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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> |
| 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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