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< title > The MPL Reference Manual: Associative Sequence</ title >
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< 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 >
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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 >
</ tr ></ table >< div class = "header-separator" ></ div >
< div class = "section" id = "associative-sequence" >
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< h1 >< a class = "toc-backref" href = "./concepts.html#id1401" > Associative Sequence</ a ></ h1 >
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< div class = "section" id = "id29" >
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< h3 >< a class = "subsection-title" href = "#description" name = "description" > Description</ a ></ h3 >
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< 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
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unspecified.</ p >
</ div >
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< div class = "section" id = "id30" >
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< h3 >< a class = "subsection-title" href = "#definitions" name = "definitions" > Definitions</ a ></ h3 >
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< ul class = "simple" id = "value-part" >
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< li >< span id = "key-part" ></ span > A < em > key</ em > is a part of the element type used to identify and retrieve
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the element within the sequence.</ li >
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< li > A < em > value</ em > is a part of the element type retrievied from the sequence
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by its key.</ li >
</ ul >
</ div >
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< div class = "section" id = "id31" >
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< h3 >< a class = "subsection-title" href = "#expression-requirements" name = "expression-requirements" > Expression requirements</ a ></ h3 >
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< 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 > ,
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< 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 >
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< p > In addition to the requirements defined in < a class = "reference internal" href = "./forward-sequence.html" > Forward Sequence</ a > ,
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the following must be met:</ p >
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< table border = "1" class = "docutils table" >
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< colgroup >
< col width = "33%" />
< col width = "38%" />
< col width = "29%" />
</ colgroup >
< thead valign = "bottom" >
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< tr >< th class = "head" > Expression</ th >
< th class = "head" > Type</ th >
< th class = "head" > Complexity</ th >
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</ 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 >
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< td > Boolean < a class = "reference internal" href = "./integral-constant.html" > Integral Constant</ a ></ td >
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< 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 >
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< td >< a class = "reference internal" href = "./integral-constant.html" > Integral Constant</ a ></ td >
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< 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 >
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< 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 >
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< 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 >
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< div class = "section" id = "id32" >
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< h3 >< a class = "subsection-title" href = "#expression-semantics" name = "expression-semantics" > Expression semantics</ a ></ h3 >
< p > The semantics of an expression are defined only
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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" >
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< colgroup >
< col width = "33%" />
< col width = "67%" />
</ colgroup >
< thead valign = "bottom" >
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< tr >< th class = "head" > Expression</ th >
< th class = "head" > Semantics</ th >
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</ 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 >
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< 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
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< 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
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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 >
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</ 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 > ;
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see < a class = "reference internal" href = "./count.html" > count</ a > .</ td >
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</ tr >
< tr >< td >< tt class = "literal" >< span class = "pre" >< a href = "./order.html" class = "identifier" > order</ a > < s,k> ::type</ span ></ tt ></ td >
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< 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 >
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</ 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 >
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in the sequence < tt class = "literal" >< span class = "pre" > s</ span ></ tt > ; see < a class = "reference internal" href = "./at.html" > at</ a > .</ td >
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</ 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
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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 >
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</ 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
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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 >
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</ tr >
</ tbody >
</ table >
<!-- Invariants
- - - - - - - - - -
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For any associative sequence ``s`` the following invariants always hold:
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* ??? -->
</ div >
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< div class = "section" id = "id33" >
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< h3 >< a class = "subsection-title" href = "#models" name = "models" > Models</ a ></ h3 >
< ul class = "simple" >
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< li >< a class = "reference internal" href = "./set.html" > set</ a ></ li >
< li >< a class = "reference internal" href = "./map.html" > map</ a ></ li >
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</ ul >
<!-- * |multiset| -->
</ div >
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< div class = "section" id = "id34" >
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< h3 >< a class = "subsection-title" href = "#see-also" name = "see-also" > See also</ a ></ h3 >
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< 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 >
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<!-- Sequences/Concepts//Extensible Associative Sequence |80 -->
</ div >
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< 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
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