libs/iterator/doc/RandomAccessTraversal.rst
.. 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`` | | | +-------------------------------+---------------------------------+-------------------------+----------------------+