| .. 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``| | |
| | | | | |
| +--------------------------------+-------------------------------+---------------------+ |
