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| <title>The MPL Reference Manual: Associative Sequence</title> |
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| <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> |
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| <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> |
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| <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 |
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