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