2006-09-11 22:08:18 +00:00
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.. Copyright David Abrahams 2006. Distributed under the Boost
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.. Software License, Version 1.0. (See accompanying
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.. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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2004-01-27 17:03:46 +00:00
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Random Access Traversal Concept
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...............................
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A class or built-in type ``X`` models the *Random Access Traversal*
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concept if the following expressions are valid and respect the stated
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semantics. In the table below, ``Distance`` is
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``iterator_traits<X>::difference_type`` and ``n`` represents a
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constant object of type ``Distance``.
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+------------------------------------------------------------------------------------------------------------------+
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|Random Access Traversal Iterator Requirements (in addition to Bidirectional Traversal) |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|Expression |Return Type |Operational Semantics |Assertion/ |
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| | | |Precondition |
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+===============================+=================================+=========================+======================+
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|``r += n`` |``X&`` |:: | |
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| | | | |
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| | | { | |
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| | | Distance m = n; | |
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| | | if (m >= 0) | |
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| | | while (m--) | |
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| | | ++r; | |
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| | | else | |
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| | | while (m++) | |
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| | | --r; | |
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| | | return r; | |
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| | | } | |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``a + n``, ``n + a`` |``X`` |``{ X tmp = a; return tmp| |
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| | |+= n; }`` | |
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| | | | |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``r -= n`` |``X&`` |``return r += -n`` | |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``a - n`` |``X`` |``{ X tmp = a; return tmp| |
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| | |-= n; }`` | |
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| | | | |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``b - a`` |``Distance`` |``a < b ? distance(a,b) |pre: there exists a |
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| | |: -distance(b,a)`` |value ``n`` of |
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| | | |``Distance`` such that|
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| | | |``a + n == b``. ``b |
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| | | |== a + (b - a)``. |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``a[n]`` |convertible to T |``*(a + n)`` |pre: a is a *Readable |
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| | | |Iterator* |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``a[n] = v`` |convertible to T |``*(a + n) = v`` |pre: a is a *Writable |
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| | | |iterator* |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``a < b`` |convertible to ``bool`` |``b - a > 0`` |``<`` is a total |
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| | | |ordering relation |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``a > b`` |convertible to ``bool`` |``b < a`` |``>`` is a total |
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| | | |ordering relation |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``a >= b`` |convertible to ``bool`` |``!(a < b)`` | |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``a <= b`` |convertible to ``bool`` |``!(a > b)`` | |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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|``iterator_traversal<X>::type``|Convertible to | | |
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| |``random_access_traversal_tag`` | | |
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+-------------------------------+---------------------------------+-------------------------+----------------------+
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