<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> <title>The MPL Reference Manual: Associative Sequence</title> <link rel="stylesheet" href="../style.css" type="text/css" /> </head> <body class="docframe refmanual"> <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> <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> </tr></table><div class="header-separator"></div> <div class="section" id="associative-sequence"> <h1><a class="toc-backref" href="./concepts.html#id1401">Associative Sequence</a></h1> <div class="section" id="id29"> <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> <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 elements based on keys. Unlike associative containers in the C++ Standard Library, MPL associative sequences have no associated ordering relation. Instead, <em>type identity</em> is used to impose an equivalence relation on keys, and the order in which sequence elements are traversed during iteration is left unspecified.</p> </div> <div class="section" id="id30"> <h3><a class="subsection-title" href="#definitions" name="definitions">Definitions</a></h3> <ul class="simple" id="value-part"> <span id="key-part"></span><li>A <em>key</em> is a part of the element type used to identify and retrieve the element within the sequence.</li> <li>A <em>value</em> is a part of the element type retrievied from the sequence by its key.</li> </ul> </div> <div class="section" id="id31"> <h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3> <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>, <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> <p>In addition to the requirements defined in <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, the following must be met:</p> <table border="1" class="docutils table"> <colgroup> <col width="33%" /> <col width="38%" /> <col width="29%" /> </colgroup> <thead valign="bottom"> <tr><th class="head">Expression</th> <th class="head">Type</th> <th class="head">Complexity</th> </tr> </thead> <tbody valign="top"> <tr><td><tt class="literal"><span class="pre"><a href="./has-key.html" class="identifier">has_key</a><s,k>::type</span></tt></td> <td>Boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a></td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./count.html" class="identifier">count</a><s,k>::type</span></tt></td> <td><a class="reference internal" href="./integral-constant.html">Integral Constant</a></td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./order.html" class="identifier">order</a><s,k>::type</span></tt></td> <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> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./at.html" class="identifier">at</a><s,k>::type</span></tt></td> <td>Any type</td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./at.html" class="identifier">at</a><s,k,def>::type</span></tt></td> <td>Any type</td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./key-type.html" class="identifier">key_type</a><s,x>::type</span></tt></td> <td>Any type</td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./value-type.html" class="identifier">value_type</a><s,x>::type</span></tt></td> <td>Any type</td> <td>Amortized constant time</td> </tr> </tbody> </table> </div> <div class="section" id="id32"> <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> <p>The semantics of an expression are defined only where they differ from, or are not defined in <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>.</p> <table border="1" class="docutils table"> <colgroup> <col width="33%" /> <col width="67%" /> </colgroup> <thead valign="bottom"> <tr><th class="head">Expression</th> <th class="head">Semantics</th> </tr> </thead> <tbody valign="top"> <tr><td><tt class="literal"><span class="pre"><a href="./has-key.html" class="identifier">has_key</a><s,k>::type</span></tt></td> <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 <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 elements 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> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./count.html" class="identifier">count</a><s,k>::type</span></tt></td> <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>; see <a class="reference internal" href="./count.html">count</a>.</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./order.html" class="identifier">order</a><s,k>::type</span></tt></td> <td>A unique unsigned <a class="reference internal" href="./integral-constant.html">Integral Constant</a> associated with 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> </tr> <tr><td><pre class="first last literal-block"> <a href="./at.html" class="identifier">at</a><s,k>::type <a href="./at.html" class="identifier">at</a><s,k,def>::type </pre> </td> <td>The first element associated with 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="./at.html">at</a>.</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./key-type.html" class="identifier">key_type</a><s,x>::type</span></tt></td> <td>The key part of the element <tt class="literal"><span class="pre">x</span></tt> that would be used 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> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./value-type.html" class="identifier">value_type</a><s,x>::type</span></tt></td> <td>The value part of the element <tt class="literal"><span class="pre">x</span></tt> that would be used 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> </tr> </tbody> </table> <!-- Invariants - - - - - - - - - - For any associative sequence ``s`` the following invariants always hold: * ??? --> </div> <div class="section" id="id33"> <h3><a class="subsection-title" href="#models" name="models">Models</a></h3> <ul class="simple"> <li><a class="reference internal" href="./set.html">set</a></li> <li><a class="reference internal" href="./map.html">map</a></li> </ul> <!-- * |multiset| --> </div> <div class="section" id="id34"> <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> <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> <!-- Sequences/Concepts//Extensible Associative Sequence |80 --> </div> </div> <div class="footer-separator"></div> <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> <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> Distributed under the Boost Software License, Version 1.0. (See accompanying file 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> </html>