Bidirectional Range

Boost C++ Libraries

Bidirectional Range

Notation

`X`	A type that is a model of Bidirectional Range.
`a`	Object of type X.

Description

This concept provides access to iterators that traverse in both directions (forward and reverse). The boost::range_iterator<X>::type iterator must meet all of the requirements of Bidirectional Traversal Iterator.

Refinement of

Associated types

Reverse Iterator type	`boost::range_reverse_iterator<X>::type`	The type of iterator used to iterate through a Range's elements in reverse order. The iterator's value type is expected to be the Range's value type. A conversion from the reverse iterator type to the const reverse iterator type must exist.
Const reverse iterator type	`boost::range_reverse_iterator<const X>::type`	A type of reverse iterator that may be used to examine, but not to modify, a Range's elements.

Valid expressions

Name	Expression	Return type	Semantics
Beginning of range	`boost::rbegin(a)`	`boost::range_reverse_iterator<X>::type` if `a` is mutable `boost::range_reverse_iterator<const X>::type` otherwise.	Equivalent to `boost::range_reverse_iterator<X>::type(boost::end(a))`.
End of range	`boost::rend(a)`	`boost::range_reverse_iterator<X>::type` if `a` is mutable, `boost::range_reverse_iterator<const X>::type` otherwise.	Equivalent to `boost::range_reverse_iterator<X>::type(boost::begin(a))`.

Complexity guarantees

boost::rbegin(a) has the same complexity as boost::end(a) and boost::rend(a) has the same complexity as boost::begin(a) from Forward Range.

Invariants

Valid reverse range	For any Bidirectional Range a, `[boost::rbegin(a),boost::rend(a))` is a valid range, that is, `boost::rend(a)` is reachable from `boost::rbegin(a)` in a finite number of increments.
Completeness	An algorithm that iterates through the range `[boost::rbegin(a),boost::rend(a))` will pass through every element of `a`.

See also

Implementation of metafunctions

Implementation of functions