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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)
- Random Access Traversal Concept
- ...............................
- A class or built-in type ``X`` models the *Random Access Traversal*
- concept if the following expressions are valid and respect the stated
- semantics. In the table below, ``Distance`` is
- ``iterator_traits<X>::difference_type`` and ``n`` represents a
- constant object of type ``Distance``.
- +------------------------------------------------------------------------------------------------------------------+
- |Random Access Traversal Iterator Requirements (in addition to Bidirectional Traversal) |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |Expression |Return Type |Operational Semantics |Assertion/ |
- | | | |Precondition |
- +===============================+=================================+=========================+======================+
- |``r += n`` |``X&`` |:: | |
- | | | | |
- | | | { | |
- | | | Distance m = n; | |
- | | | if (m >= 0) | |
- | | | while (m--) | |
- | | | ++r; | |
- | | | else | |
- | | | while (m++) | |
- | | | --r; | |
- | | | return r; | |
- | | | } | |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``a + n``, ``n + a`` |``X`` |``{ X tmp = a; return tmp| |
- | | |+= n; }`` | |
- | | | | |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``r -= n`` |``X&`` |``return r += -n`` | |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``a - n`` |``X`` |``{ X tmp = a; return tmp| |
- | | |-= n; }`` | |
- | | | | |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``b - a`` |``Distance`` |``a < b ? distance(a,b) |pre: there exists a |
- | | |: -distance(b,a)`` |value ``n`` of |
- | | | |``Distance`` such that|
- | | | |``a + n == b``. ``b |
- | | | |== a + (b - a)``. |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``a[n]`` |convertible to T |``*(a + n)`` |pre: a is a *Readable |
- | | | |Iterator* |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``a[n] = v`` |convertible to T |``*(a + n) = v`` |pre: a is a *Writable |
- | | | |iterator* |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``a < b`` |convertible to ``bool`` |``b - a > 0`` |``<`` is a total |
- | | | |ordering relation |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``a > b`` |convertible to ``bool`` |``b < a`` |``>`` is a total |
- | | | |ordering relation |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``a >= b`` |convertible to ``bool`` |``!(a < b)`` | |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``a <= b`` |convertible to ``bool`` |``!(a > b)`` | |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
- |``iterator_traversal<X>::type``|Convertible to | | |
- | |``random_access_traversal_tag`` | | |
- +-------------------------------+---------------------------------+-------------------------+----------------------+
|