1<?xml version="1.0" encoding="utf-8" ?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4<head> 5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 6<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> 7<title>The MPL Reference Manual: Associative Sequence</title> 8<link rel="stylesheet" href="../style.css" type="text/css" /> 9</head> 10<body class="docframe refmanual"> 11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./back-extensible-sequence.html" class="navigation-link">Prev</a> <a href="./extensible-associative-sequence.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./back-extensible-sequence.html" class="navigation-link">Back</a> <a href="./extensible-associative-sequence.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 12<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./sequences.html" class="navigation-link">Sequences</a> / <a href="./concepts.html" class="navigation-link">Concepts</a> / <a href="./associative-sequence.html" class="navigation-link">Associative Sequence</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="associative-sequence"> 15<h1><a class="toc-backref" href="./concepts.html#id1401">Associative Sequence</a></h1> 16<div class="section" id="id29"> 17<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 18<p>An <a class="reference internal" href="./associative-sequence.html">Associative Sequence</a> is a <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> that allows efficient retrieval of 19elements based on keys. Unlike associative containers in the C++ Standard Library, 20MPL associative sequences have no associated ordering relation. Instead, 21<em>type identity</em> is used to impose an equivalence relation on keys, and the 22order in which sequence elements are traversed during iteration is left 23unspecified.</p> 24</div> 25<div class="section" id="id30"> 26<h3><a class="subsection-title" href="#definitions" name="definitions">Definitions</a></h3> 27<ul class="simple" id="value-part"> 28<span id="key-part"></span><li>A <em>key</em> is a part of the element type used to identify and retrieve 29the element within the sequence.</li> 30<li>A <em>value</em> is a part of the element type retrievied from the sequence 31by its key.</li> 32</ul> 33</div> 34<div class="section" id="id31"> 35<h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3> 36<p>In the following table and subsequent specifications, <tt class="literal"><span class="pre">s</span></tt> is an <a class="reference internal" href="./associative-sequence.html">Associative Sequence</a>, 37<tt class="literal"><span class="pre">x</span></tt> is a sequence element, and <tt class="literal"><span class="pre">k</span></tt> and <tt class="literal"><span class="pre">def</span></tt> are arbitrary types.</p> 38<p>In addition to the requirements defined in <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, 39the following must be met:</p> 40<table border="1" class="docutils table"> 41<colgroup> 42<col width="33%" /> 43<col width="38%" /> 44<col width="29%" /> 45</colgroup> 46<thead valign="bottom"> 47<tr><th class="head">Expression</th> 48<th class="head">Type</th> 49<th class="head">Complexity</th> 50</tr> 51</thead> 52<tbody valign="top"> 53<tr><td><tt class="literal"><span class="pre"><a href="./has-key.html" class="identifier">has_key</a><s,k>::type</span></tt></td> 54<td>Boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a></td> 55<td>Amortized constant time</td> 56</tr> 57<tr><td><tt class="literal"><span class="pre"><a href="./count.html" class="identifier">count</a><s,k>::type</span></tt></td> 58<td><a class="reference internal" href="./integral-constant.html">Integral Constant</a></td> 59<td>Amortized constant time</td> 60</tr> 61<tr><td><tt class="literal"><span class="pre"><a href="./order.html" class="identifier">order</a><s,k>::type</span></tt></td> 62<td><a class="reference internal" href="./integral-constant.html">Integral Constant</a> or <tt class="literal"><span class="pre"><a href="./void.html" class="identifier">void_</a></span></tt></td> 63<td>Amortized constant time</td> 64</tr> 65<tr><td><tt class="literal"><span class="pre"><a href="./at.html" class="identifier">at</a><s,k>::type</span></tt></td> 66<td>Any type</td> 67<td>Amortized constant time</td> 68</tr> 69<tr><td><tt class="literal"><span class="pre"><a href="./at.html" class="identifier">at</a><s,k,def>::type</span></tt></td> 70<td>Any type</td> 71<td>Amortized constant time</td> 72</tr> 73<tr><td><tt class="literal"><span class="pre"><a href="./key-type.html" class="identifier">key_type</a><s,x>::type</span></tt></td> 74<td>Any type</td> 75<td>Amortized constant time</td> 76</tr> 77<tr><td><tt class="literal"><span class="pre"><a href="./value-type.html" class="identifier">value_type</a><s,x>::type</span></tt></td> 78<td>Any type</td> 79<td>Amortized constant time</td> 80</tr> 81</tbody> 82</table> 83</div> 84<div class="section" id="id32"> 85<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 86<p>The semantics of an expression are defined only 87where they differ from, or are not defined in <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>.</p> 88<table border="1" class="docutils table"> 89<colgroup> 90<col width="33%" /> 91<col width="67%" /> 92</colgroup> 93<thead valign="bottom"> 94<tr><th class="head">Expression</th> 95<th class="head">Semantics</th> 96</tr> 97</thead> 98<tbody valign="top"> 99<tr><td><tt class="literal"><span class="pre"><a href="./has-key.html" class="identifier">has_key</a><s,k>::type</span></tt></td> 100<td>A boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a> <tt class="literal"><span class="pre">c</span></tt> such that 101<tt class="literal"><span class="pre">c::value</span> <span class="pre">==</span> <span class="pre">true</span></tt> if and only if there is one or more 102elements with the key <tt class="literal"><span class="pre">k</span></tt> in <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./has-key.html">has_key</a>.</td> 103</tr> 104<tr><td><tt class="literal"><span class="pre"><a href="./count.html" class="identifier">count</a><s,k>::type</span></tt></td> 105<td>The number of elements with the key <tt class="literal"><span class="pre">k</span></tt> in <tt class="literal"><span class="pre">s</span></tt>; 106see <a class="reference internal" href="./count.html">count</a>.</td> 107</tr> 108<tr><td><tt class="literal"><span class="pre"><a href="./order.html" class="identifier">order</a><s,k>::type</span></tt></td> 109<td>A unique unsigned <a class="reference internal" href="./integral-constant.html">Integral Constant</a> associated 110with the key <tt class="literal"><span class="pre">k</span></tt> in the sequence <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./order.html">order</a>.</td> 111</tr> 112<tr><td><pre class="first last literal-block"> 113<a href="./at.html" class="identifier">at</a><s,k>::type 114<a href="./at.html" class="identifier">at</a><s,k,def>::type 115</pre> 116</td> 117<td>The first element associated with the key <tt class="literal"><span class="pre">k</span></tt> 118in the sequence <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./at.html">at</a>.</td> 119</tr> 120<tr><td><tt class="literal"><span class="pre"><a href="./key-type.html" class="identifier">key_type</a><s,x>::type</span></tt></td> 121<td>The key part of the element <tt class="literal"><span class="pre">x</span></tt> that would be 122used to identify <tt class="literal"><span class="pre">x</span></tt> in <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./key-type.html">key_type</a>.</td> 123</tr> 124<tr><td><tt class="literal"><span class="pre"><a href="./value-type.html" class="identifier">value_type</a><s,x>::type</span></tt></td> 125<td>The value part of the element <tt class="literal"><span class="pre">x</span></tt> that would be 126used for <tt class="literal"><span class="pre">x</span></tt> in <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./value-type.html">value_type</a>.</td> 127</tr> 128</tbody> 129</table> 130<!-- Invariants 131- - - - - - - - - - 132 133For any associative sequence ``s`` the following invariants always hold: 134 135 * ??? --> 136</div> 137<div class="section" id="id33"> 138<h3><a class="subsection-title" href="#models" name="models">Models</a></h3> 139<ul class="simple"> 140<li><a class="reference internal" href="./set.html">set</a></li> 141<li><a class="reference internal" href="./map.html">map</a></li> 142</ul> 143<!-- * |multiset| --> 144</div> 145<div class="section" id="id34"> 146<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 147<p><a class="reference internal" href="./sequences.html">Sequences</a>, <a class="reference internal" href="./extensible-associative-sequence.html">Extensible Associative Sequence</a>, <a class="reference internal" href="./has-key.html">has_key</a>, <a class="reference internal" href="./count.html">count</a>, <a class="reference internal" href="./order.html">order</a>, <a class="reference internal" href="./at.html">at</a>, <a class="reference internal" href="./key-type.html">key_type</a>, <a class="reference internal" href="./value-type.html">value_type</a></p> 148<!-- Sequences/Concepts//Extensible Associative Sequence |80 --> 149</div> 150</div> 151 152<div class="footer-separator"></div> 153<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./back-extensible-sequence.html" class="navigation-link">Prev</a> <a href="./extensible-associative-sequence.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./back-extensible-sequence.html" class="navigation-link">Back</a> <a href="./extensible-associative-sequence.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 154<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 155Distributed under the Boost Software License, Version 1.0. (See accompanying 156file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> 157</html> 158