2006-09-11 22:08:18 +00:00
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.. Copyright David Abrahams 2006. Distributed under the Boost
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.. Software License, Version 1.0. (See accompanying
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.. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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2004-01-27 17:03:46 +00:00
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Bidirectional Traversal Concept
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...............................
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A class or built-in type ``X`` models the *Bidirectional Traversal*
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concept if, in addition to ``X`` meeting the requirements of Forward
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Traversal Iterator, the following expressions are valid and respect
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the stated semantics.
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+--------------------------------------------------------------------------------------+
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|Bidirectional Traversal Iterator Requirements (in addition to Forward Traversal |
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|Iterator) |
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+--------------------------------+-------------------------------+---------------------+
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|Expression |Return Type |Assertion/Semantics /|
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| | |Pre-/Post-condition |
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+================================+===============================+=====================+
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|``--r`` |``X&`` |pre: there exists |
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| | |``s`` such that ``r |
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| | |== ++s``. post: |
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| | |``s`` is |
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| | |dereferenceable. |
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| | |``--(++r) == r``. |
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| | |``--r == --s`` |
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| | |implies ``r == |
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| | |s``. ``&r == &--r``. |
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+--------------------------------+-------------------------------+---------------------+
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|``r--`` |convertible to ``const X&`` |:: |
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| | | |
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| | | { |
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| | | X tmp = r; |
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| | | --r; |
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| | | return tmp; |
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| | | } |
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+--------------------------------+-------------------------------+---------------------+
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|``iterator_traversal<X>::type`` |Convertible to | |
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| |``bidirectional_traversal_tag``| |
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| | | |
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+--------------------------------+-------------------------------+---------------------+
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