ceph/src/boost/libs/iterator/doc/BidirectionalTraversal.html

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  12 <h1 class="title">Bidirectional Traversal Concept</h1>
  13
  14 <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
  15 <!-- Software License, Version 1.0. (See accompanying -->
  16 <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
  17 <p>A class or built-in type <tt class="docutils literal"><span class="pre">X</span></tt> models the <em>Bidirectional Traversal</em>
  18 concept if, in addition to <tt class="docutils literal"><span class="pre">X</span></tt> meeting the requirements of Forward
  19 Traversal Iterator, the following expressions are valid and respect
  20 the stated semantics.</p>
  21 <table border="1" class="docutils">
  22 <colgroup>
  23 <col width="38%" />
  24 <col width="37%" />
  25 <col width="25%" />
  26 </colgroup>
  27 <thead valign="bottom">
  28 <tr><th class="head" colspan="3">Bidirectional Traversal Iterator Requirements (in addition to Forward Traversal
  29 Iterator)</th>
  30 </tr>
  31 <tr><th class="head">Expression</th>
  32 <th class="head">Return Type</th>
  33 <th class="head">Assertion/Semantics /
  34 Pre-/Post-condition</th>
  35 </tr>
  36 </thead>
  37 <tbody valign="top">
  38 <tr><td><tt class="docutils literal"><span class="pre">--r</span></tt></td>
  39 <td><tt class="docutils literal"><span class="pre">X&amp;</span></tt></td>
  40 <td>pre: there exists
  41 <tt class="docutils literal"><span class="pre">s</span></tt> such that <tt class="docutils literal"><span class="pre">r</span>
  42 <span class="pre">==</span> <span class="pre">++s</span></tt>.  post:
  43 <tt class="docutils literal"><span class="pre">s</span></tt> is
  44 dereferenceable.
  45 <tt class="docutils literal"><span class="pre">--(++r)</span> <span class="pre">==</span> <span class="pre">r</span></tt>.
  46 <tt class="docutils literal"><span class="pre">--r</span> <span class="pre">==</span> <span class="pre">--s</span></tt>
  47 implies <tt class="docutils literal"><span class="pre">r</span> <span class="pre">==</span>
  48 <span class="pre">s</span></tt>. <tt class="docutils literal"><span class="pre">&amp;r</span> <span class="pre">==</span> <span class="pre">&amp;--r</span></tt>.</td>
  49 </tr>
  50 <tr><td><tt class="docutils literal"><span class="pre">r--</span></tt></td>
  51 <td>convertible to <tt class="docutils literal"><span class="pre">const</span> <span class="pre">X&amp;</span></tt></td>
  52 <td><pre class="first last literal-block">
  53 {
  54   X tmp = r;
  55   --r;
  56   return tmp;
  57 }
  58 </pre>
  59 </td>
  60 </tr>
  61 <tr><td><tt class="docutils literal"><span class="pre">iterator_traversal&lt;X&gt;::type</span></tt></td>
  62 <td>Convertible to
  63 <tt class="docutils literal"><span class="pre">bidirectional_traversal_tag</span></tt></td>
  64 <td>&nbsp;</td>
  65 </tr>
  66 </tbody>
  67 </table>
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