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<title>Associative
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Sequence</title>
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<div class="section" lang="en">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="fusion.sequence.concepts.associative_sequence"></a><a href="associative_sequence.html" title="Associative
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Sequence">Associative
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Sequence</a></h4></div></div></div>
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<a name="fusion.sequence.concepts.associative_sequence.description"></a><h5>
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<a name="id495917"></a>
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<a href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.description">Description</a>
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</h5>
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<p>
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An Associative Sequence allows efficient retrieval of elements based on
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keys. Like associative sequences in <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>,
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and unlike associative containers in <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>,
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Fusion associative sequences have no implied ordering relation. Instead,
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type identity is used to impose an equivalence relation on keys, and the
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order in which sequence elements are traversed during iteration is left
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unspecified. In addition, unlike <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>,
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Associative Sequences have mutable iterators. This is due to the fact that
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there is no associated ordering relation and the runtime value of the keys
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themselves do not have any effect on the associativity of the sequence.
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</p>
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<div class="variablelist">
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<p class="title"><b>Notation</b></p>
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<dl>
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<dt><span class="term"><tt class="computeroutput"><span class="identifier">s</span></tt></span></dt>
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<dd><p>
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An Associative Sequence
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</p></dd>
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<dt><span class="term"><tt class="computeroutput"><span class="identifier">S</span></tt></span></dt>
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<dd><p>
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An Associative Sequence type
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</p></dd>
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<dt><span class="term"><tt class="computeroutput"><span class="identifier">K</span></tt></span></dt>
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<dd><p>
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An arbitrary <span class="emphasis"><em>key</em></span> type
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</p></dd>
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<dt><span class="term"><tt class="computeroutput"><span class="identifier">o</span></tt></span></dt>
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<dd><p>
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An arbitrary object
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</p></dd>
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<dt><span class="term"><tt class="computeroutput"><span class="identifier">e</span></tt></span></dt>
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<dd><p>
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A Sequence element
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</p></dd>
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</dl>
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</div>
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<a name="fusion.sequence.concepts.associative_sequence.valid_expressions"></a><h5>
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<a name="id496106"></a>
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<a href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.valid_expressions">Valid
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Expressions</a>
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</h5>
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<p>
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For any Associative Sequence the following expressions must be valid:
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</p>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Expression
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</p>
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</th>
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<th>
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<p>
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Return type
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</p>
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</th>
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<th>
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<p>
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Type Requirements
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</p>
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</th>
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<th>
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<p>
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Runtime Complexity
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><a href="../intrinsic/functions/has_key.html" title="has_key"><tt class="computeroutput"><span class="identifier">has_key</span></tt></a><span class="special"><</span><span class="identifier">K</span><span class="special">>(</span><span class="identifier">s</span><span class="special">)</span></tt>
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</p>
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</td>
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<td>
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<p>
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<a href="http://www.boost.org/libs/mpl/doc/refmanual/integral-constant.html" target="_top">MPL
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Boolean Constant</a>. Convertible to bool.
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</p>
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</td>
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<td>
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<p>
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</p>
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</td>
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<td>
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<p>
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Constant
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><a href="../intrinsic/functions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">at_key</span></tt></a><span class="special"><</span><span class="identifier">K</span><span class="special">>(</span><span class="identifier">s</span><span class="special">)</span></tt>
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</p>
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</td>
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<td>
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<p>
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Any type
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</p>
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</td>
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<td>
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<p>
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</p>
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</td>
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<td>
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<p>
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Constant
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><a href="../intrinsic/functions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">at_key</span></tt></a><span class="special"><</span><span class="identifier">K</span><span class="special">>(</span><span class="identifier">s</span><span class="special">)</span>
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<span class="special">=</span> <span class="identifier">o</span></tt>
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</p>
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</td>
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<td>
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<p>
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Any type
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</p>
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</td>
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<td>
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<p>
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<tt class="computeroutput"><span class="identifier">s</span></tt> is mutable and
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<tt class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
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<span class="identifier">o</span></tt>, where <tt class="computeroutput"><span class="identifier">e</span></tt> is the first element in the
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sequence, is a valid expression.
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</p>
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</td>
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<td>
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<p>
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Constant
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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<a name="fusion.sequence.concepts.associative_sequence.result_type_expressions"></a><h5>
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<a name="id496491"></a>
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<a href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.result_type_expressions">Result
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Type Expressions</a>
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</h5>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Expression
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</p>
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</th>
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<th>
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<p>
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Compile Time Complexity
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><a href="../intrinsic/metafunctions/has_key.html" title="has_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">has_key</span></tt></a><span class="special"><</span><span class="identifier">S</span><span class="special">,</span>
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<span class="identifier">K</span><span class="special">>::</span><span class="identifier">type</span></tt>
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</p>
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</td>
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<td>
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<p>
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Amortized constant time
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><a href="../intrinsic/metafunctions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></tt></a><span class="special"><</span><span class="identifier">S</span><span class="special">,</span>
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<span class="identifier">K</span><span class="special">>::</span><span class="identifier">type</span></tt>
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</p>
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</td>
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<td>
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<p>
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Amortized constant time
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><a href="../intrinsic/metafunctions/value_at_key.html" title="value_at_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at_key</span></tt></a><span class="special"><</span><span class="identifier">S</span><span class="special">,</span>
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<span class="identifier">K</span><span class="special">>::</span><span class="identifier">type</span></tt>
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</p>
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</td>
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<td>
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<p>
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Amortized constant time
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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<div class="sidebar"><p>
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<span class="inlinemediaobject"><img src="../../../images/note.png" alt="note"></span> <tt class="computeroutput"><a href="../intrinsic/metafunctions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></tt></a><span class="special"><</span><span class="identifier">S</span><span class="special">,</span> <span class="identifier">K</span><span class="special">></span></tt> returns the actual type returned by
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<tt class="computeroutput"><a href="../intrinsic/functions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">at_key</span></tt></a><span class="special"><</span><span class="identifier">K</span><span class="special">>(</span><span class="identifier">s</span><span class="special">)</span></tt>. In
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most cases, this is a reference. Hence, there is no way to know the exact
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element type using <tt class="computeroutput"><a href="../intrinsic/metafunctions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></tt></a><span class="special"><</span><span class="identifier">S</span><span class="special">,</span> <span class="identifier">K</span><span class="special">></span></tt>.The element at <tt class="computeroutput"><span class="identifier">K</span></tt>
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may actually be a reference to begin with. For this purpose, you can use
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<tt class="computeroutput"><a href="../intrinsic/metafunctions/value_at_key.html" title="value_at_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at_key</span></tt></a><span class="special"><</span><span class="identifier">S</span><span class="special">,</span> <span class="identifier">N</span><span class="special">></span></tt>.
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</p></div>
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<a name="fusion.sequence.concepts.associative_sequence.expression_semantics"></a><h5>
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<a name="id497066"></a>
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<a href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.expression_semantics">Expression
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Semantics</a>
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</h5>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Expression
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</p>
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</th>
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<th>
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<p>
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Semantics
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><a href="../intrinsic/functions/has_key.html" title="has_key"><tt class="computeroutput"><span class="identifier">has_key</span></tt></a><span class="special"><</span><span class="identifier">K</span><span class="special">>(</span><span class="identifier">s</span><span class="special">)</span></tt>
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</p>
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</td>
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<td>
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<p>
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A boolean Integral Constant <tt class="computeroutput"><span class="identifier">c</span></tt>
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such that <tt class="computeroutput"><span class="identifier">c</span><span class="special">::</span><span class="identifier">value</span> <span class="special">==</span>
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<span class="keyword">true</span></tt> if and only if there
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is one or more elements with the key <tt class="computeroutput"><span class="identifier">k</span></tt>
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in <tt class="computeroutput"><span class="identifier">s</span></tt>; see <a href="../intrinsic/functions/has_key.html" title="has_key"><tt class="computeroutput"><span class="identifier">has_key</span></tt></a>.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><a href="../intrinsic/functions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">at_key</span></tt></a><span class="special"><</span><span class="identifier">K</span><span class="special">>(</span><span class="identifier">s</span><span class="special">)</span></tt>
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</p>
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</td>
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<td>
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<p>
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The element associated with the key <tt class="computeroutput"><span class="identifier">K</span></tt>
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in the sequence <tt class="computeroutput"><span class="identifier">s</span></tt>;
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see <a href="../intrinsic/functions/at.html" title="at"><tt class="computeroutput"><span class="identifier">at</span></tt></a>.
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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<a name="fusion.sequence.concepts.associative_sequence.models"></a><h5>
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<a name="id497387"></a>
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<a href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.models">Models</a>
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</h5>
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<div class="itemizedlist"><ul type="disc">
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<td align="right"><div class="copyright-footer">Copyright © 2001-2007 Joel de Guzman, Dan Marsden, Tobias
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Schwinger<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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