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HTML
135 lines
7.8 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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<head>
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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>Random Access 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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<body>
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<div class="document" id="random-access-traversal-concept">
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<h1 class="title">Random Access 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>Random Access Traversal</em>
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concept if the following expressions are valid and respect the stated
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semantics. In the table below, <tt class="docutils literal"><span class="pre">Distance</span></tt> is
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<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
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constant object of type <tt class="docutils literal"><span class="pre">Distance</span></tt>.</p>
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<table border="1" class="docutils">
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<colgroup>
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<col width="28%" />
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<col width="30%" />
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<col width="23%" />
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<col width="20%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th class="head" colspan="4">Random Access Traversal Iterator Requirements (in addition to Bidirectional Traversal)</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">Operational Semantics</th>
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<th class="head">Assertion/
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Precondition</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> <span class="pre">+=</span> <span class="pre">n</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 class="first last literal-block">
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{
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Distance m = n;
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if (m >= 0)
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while (m--)
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++r;
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else
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while (m++)
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--r;
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return r;
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}
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</pre>
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</td>
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<td> </td>
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</tr>
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<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>
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<td><tt class="docutils literal"><span class="pre">X</span></tt></td>
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<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>
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<span class="pre">+=</span> <span class="pre">n;</span> <span class="pre">}</span></tt></td>
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<td> </td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">r</span> <span class="pre">-=</span> <span class="pre">n</span></tt></td>
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<td><tt class="docutils literal"><span class="pre">X&</span></tt></td>
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<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>
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<td> </td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre">-</span> <span class="pre">n</span></tt></td>
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<td><tt class="docutils literal"><span class="pre">X</span></tt></td>
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<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>
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<span class="pre">-=</span> <span class="pre">n;</span> <span class="pre">}</span></tt></td>
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<td> </td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">b</span> <span class="pre">-</span> <span class="pre">a</span></tt></td>
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<td><tt class="docutils literal"><span class="pre">Distance</span></tt></td>
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<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>
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<span class="pre">:</span> <span class="pre">-distance(b,a)</span></tt></td>
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<td>pre: there exists a
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value <tt class="docutils literal"><span class="pre">n</span></tt> of
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<tt class="docutils literal"><span class="pre">Distance</span></tt> such that
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<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>
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<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>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">a[n]</span></tt></td>
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<td>convertible to T</td>
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<td><tt class="docutils literal"><span class="pre">*(a</span> <span class="pre">+</span> <span class="pre">n)</span></tt></td>
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<td>pre: a is a <em>Readable
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Iterator</em></td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">a[n]</span> <span class="pre">=</span> <span class="pre">v</span></tt></td>
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<td>convertible to T</td>
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<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>
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<td>pre: a is a <em>Writable
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iterator</em></td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre"><</span> <span class="pre">b</span></tt></td>
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<td>convertible to <tt class="docutils literal"><span class="pre">bool</span></tt></td>
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<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>
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<td><tt class="docutils literal"><span class="pre"><</span></tt> is a total
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ordering relation</td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre">></span> <span class="pre">b</span></tt></td>
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<td>convertible to <tt class="docutils literal"><span class="pre">bool</span></tt></td>
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<td><tt class="docutils literal"><span class="pre">b</span> <span class="pre"><</span> <span class="pre">a</span></tt></td>
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<td><tt class="docutils literal"><span class="pre">></span></tt> is a total
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ordering relation</td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre">>=</span> <span class="pre">b</span></tt></td>
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<td>convertible to <tt class="docutils literal"><span class="pre">bool</span></tt></td>
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<td><tt class="docutils literal"><span class="pre">!(a</span> <span class="pre"><</span> <span class="pre">b)</span></tt></td>
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<td> </td>
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</tr>
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<tr><td><tt class="docutils literal"><span class="pre">a</span> <span class="pre"><=</span> <span class="pre">b</span></tt></td>
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<td>convertible to <tt class="docutils literal"><span class="pre">bool</span></tt></td>
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<td><tt class="docutils literal"><span class="pre">!(a</span> <span class="pre">></span> <span class="pre">b)</span></tt></td>
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<td> </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">random_access_traversal_tag</span></tt></td>
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<td> </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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<div class="footer">
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<hr class="footer" />
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<a class="reference external" href="RandomAccessTraversal.rst">View document source</a>.
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Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
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</div>
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</body>
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