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- <?xml version="1.0"?>
- <concept name="BidirectionalIterator" category="Iterator"><!--
- Based on concepts from the SGI Standard Template Library documentation:
- Copyright (c) 1996-1999
- Silicon Graphics Computer Systems, Inc.
- Copyright (c) 1994
- Hewlett-Packard Company
- --><!--
- Copyright 2000-2001 University of Notre Dame du Lac.
- Copyright 2001-2002 Indiana University.
- Some concepts based on versions from the MTL draft manual and Boost Graph
- and Property Map documentation:
- Copyright (c) Jeremy Siek, Lie-Quan Lee, and Andrew Lumsdaine 2000
- -->
- <param name="Iter" role="iterator-type"/>
- <use-header name="iterator"/>
- <models-sentence>The iterator type <arg num="1"/> must be a model of <self/>.</models-sentence>
- <description>
- <para>A bidirectional iterator is an iterator that can read through a sequence
- of values. It can move in either direction through the sequence, and can
- be either mutable (data pointed to by it can be changed) or not mutable.</para>
- <para>An iterator represents a position in a sequence. Therefore, the
- iterator can point into the sequence (returning a value when dereferenced
- and being incrementable), or be off-the-end (and not dereferenceable or
- incrementable).</para>
- </description>
- <associated-type name="value_type">
- <get-member-type name="value_type">
- <apply-template name="std::iterator_traits">
- <type name="Iter"/>
- </apply-template>
- </get-member-type>
- <description><simpara>The value type of the iterator</simpara></description>
- </associated-type>
- <refines const="no" concept="ForwardIterator"/>
- <notation variables="i j">
- <sample-value>
- <type name="Iter"/>
- </sample-value>
- </notation>
- <associated-type name="category">
- <get-member-type name="iterator_category">
- <apply-template name="std::iterator_traits">
- <type name="Iter"/>
- </apply-template>
- </get-member-type>
- <description><simpara>The category of the iterator</simpara></description>
- </associated-type>
- <notation variables="x">
- <sample-value>
- <type name="value_type"/>
- </sample-value>
- </notation>
- <valid-type-expression name="Category tag">
- <description/>
- <type name="category"/>
- <return-type>
- <derived-from testable="yes">
- <type name="std::bidirectional_iterator_tag"/>
- </derived-from>
- </return-type>
- </valid-type-expression>
- <valid-expression name="Predecrement">
- <predecrement>
- <sample-value><reference-to><type name="Iter"/></reference-to></sample-value>
- </predecrement>
- <return-type>
- <require-same-type testable="yes">
- <reference-to><type name="Iter"/></reference-to>
- </require-same-type>
- </return-type>
- <precondition><code>i</code> is incrementable (not
- off-the-end) and some dereferenceable iterator <code>j</code> exists
- such that <code>i == ++j</code></precondition>
- </valid-expression>
- <valid-expression name="Postdecrement">
- <postdecrement>
- <sample-value><reference-to><type name="Iter"/></reference-to></sample-value>
- </postdecrement>
- <return-type>
- <require-same-type testable="yes"><type name="Iter"/></require-same-type>
- </return-type>
- <precondition>Same as for predecrement</precondition>
- <semantics>Equivalent to <code>{Iter j = i; --i; return j;}</code></semantics>
- <postcondition><code>i</code> is dereferenceable or
- off-the-end</postcondition>
- </valid-expression>
- <complexity>
- All iterator operations must take amortized constant time.
- </complexity>
- <invariant name="Predecrement must return object">
- <code>&i = &(--i)</code>
- </invariant>
- <invariant name="Unique path through sequence">
- <code>i == j</code> implies <code>--i == --j</code>
- </invariant>
- <invariant name="Increment and decrement are inverses">
- <code>++i; --i;</code> and <code>--i; ++i;</code> must end up with the
- value of <code>i</code> unmodified, if <code>i</code> both of the
- operations in the pair are valid.
- </invariant>
- <example-model>
- <pointer-to>
- <type name="T"/>
- </pointer-to>
- </example-model>
- <example-model>
- <get-member-type name="iterator">
- <apply-template name="std::list">
- <type name="T"/>
- </apply-template>
- </get-member-type>
- </example-model>
- <see-also concept="RandomAccessIterator"/>
- </concept>
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