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- <h1 class="title">Random Access 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>Random Access Traversal</em>
- concept if the following expressions are valid and respect the stated
- semantics. In the table below, <tt class="docutils literal"><span class="pre">Distance</span></tt> is
- <tt class="docutils literal"><span class="pre">iterator_traits<X>::difference_type</span></tt> and <tt class="docutils literal"><span class="pre">n</span></tt> represents a
- constant object of type <tt class="docutils literal"><span class="pre">Distance</span></tt>.</p>
- <table border="1" class="docutils">
- <colgroup>
- <col width="28%" />
- <col width="30%" />
- <col width="23%" />
- <col width="20%" />
- </colgroup>
- <thead valign="bottom">
- <tr><th class="head" colspan="4">Random Access Traversal Iterator Requirements (in addition to Bidirectional Traversal)</th>
- </tr>
- <tr><th class="head">Expression</th>
- <th class="head">Return Type</th>
- <th class="head">Operational Semantics</th>
- <th class="head">Assertion/
- Precondition</th>
- </tr>
- </thead>
- <tbody valign="top">
- <tr><td><tt class="docutils literal"><span class="pre">r</span> <span class="pre">+=</span> <span class="pre">n</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">X&</span></tt></td>
- <td><pre class="first last literal-block">
- {
- Distance m = n;
- if (m >= 0)
- while (m--)
- ++r;
- else
- while (m++)
- --r;
- return r;
- }
- </pre>
- </td>
- <td> </td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre">+</span> <span class="pre">n</span></tt>, <tt class="docutils literal"><span class="pre">n</span> <span class="pre">+</span> <span class="pre">a</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">X</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">{</span> <span class="pre">X</span> <span class="pre">tmp</span> <span class="pre">=</span> <span class="pre">a;</span> <span class="pre">return</span> <span class="pre">tmp</span>
- <span class="pre">+=</span> <span class="pre">n;</span> <span class="pre">}</span></tt></td>
- <td> </td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">r</span> <span class="pre">-=</span> <span class="pre">n</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">X&</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">return</span> <span class="pre">r</span> <span class="pre">+=</span> <span class="pre">-n</span></tt></td>
- <td> </td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre">-</span> <span class="pre">n</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">X</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">{</span> <span class="pre">X</span> <span class="pre">tmp</span> <span class="pre">=</span> <span class="pre">a;</span> <span class="pre">return</span> <span class="pre">tmp</span>
- <span class="pre">-=</span> <span class="pre">n;</span> <span class="pre">}</span></tt></td>
- <td> </td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">b</span> <span class="pre">-</span> <span class="pre">a</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">Distance</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">a</span> <span class="pre"><</span> <span class="pre">b</span> <span class="pre">?</span> <span class="pre">distance(a,b)</span>
- <span class="pre">:</span> <span class="pre">-distance(b,a)</span></tt></td>
- <td>pre: there exists a
- value <tt class="docutils literal"><span class="pre">n</span></tt> of
- <tt class="docutils literal"><span class="pre">Distance</span></tt> such that
- <tt class="docutils literal"><span class="pre">a</span> <span class="pre">+</span> <span class="pre">n</span> <span class="pre">==</span> <span class="pre">b</span></tt>. <tt class="docutils literal"><span class="pre">b</span>
- <span class="pre">==</span> <span class="pre">a</span> <span class="pre">+</span> <span class="pre">(b</span> <span class="pre">-</span> <span class="pre">a)</span></tt>.</td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">a[n]</span></tt></td>
- <td>convertible to T</td>
- <td><tt class="docutils literal"><span class="pre">*(a</span> <span class="pre">+</span> <span class="pre">n)</span></tt></td>
- <td>pre: a is a <em>Readable
- Iterator</em></td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">a[n]</span> <span class="pre">=</span> <span class="pre">v</span></tt></td>
- <td>convertible to T</td>
- <td><tt class="docutils literal"><span class="pre">*(a</span> <span class="pre">+</span> <span class="pre">n)</span> <span class="pre">=</span> <span class="pre">v</span></tt></td>
- <td>pre: a is a <em>Writable
- iterator</em></td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre"><</span> <span class="pre">b</span></tt></td>
- <td>convertible to <tt class="docutils literal"><span class="pre">bool</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">b</span> <span class="pre">-</span> <span class="pre">a</span> <span class="pre">></span> <span class="pre">0</span></tt></td>
- <td><tt class="docutils literal"><span class="pre"><</span></tt> is a total
- ordering relation</td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre">></span> <span class="pre">b</span></tt></td>
- <td>convertible to <tt class="docutils literal"><span class="pre">bool</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">b</span> <span class="pre"><</span> <span class="pre">a</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">></span></tt> is a total
- ordering relation</td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre">>=</span> <span class="pre">b</span></tt></td>
- <td>convertible to <tt class="docutils literal"><span class="pre">bool</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">!(a</span> <span class="pre"><</span> <span class="pre">b)</span></tt></td>
- <td> </td>
- </tr>
- <tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre"><=</span> <span class="pre">b</span></tt></td>
- <td>convertible to <tt class="docutils literal"><span class="pre">bool</span></tt></td>
- <td><tt class="docutils literal"><span class="pre">!(a</span> <span class="pre">></span> <span class="pre">b)</span></tt></td>
- <td> </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">random_access_traversal_tag</span></tt></td>
- <td> </td>
- <td> </td>
- </tr>
- </tbody>
- </table>
- </div>
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