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