Random Access Traversal Concept

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