Description

A Reversible Container is a ForwardContainer whose iterators are BidirectionalIterator. It allows backwards iteration through the container.

Refinement Of

ForwardContainer

Associated Type(s)

Two new types are introduced. In addition, the iterator type and the const iterator type must satisfy a more stringent requirement than for a ForwardContainer. The iterator and reverse iterator types must be BidirectionalIterator, not merely ForwardIterator.

Reverse iterator type	X::reverse_iterator	A ReverseIterator adaptor whose base iterator type is the container's iterator type. Incrementing an object of type reverse_iterator moves backwards through the container: the ReverseIterator adaptor maps operator++ to operator--.
Const reverse iterator type	X::const_reverse_iterator	A ReverseIterator adaptor whose base iterator type is the container's const iterator type. [1]

Notation

X	A type that is a model of Reversible Container
a, b	Object of type X

Definitions

Valid Expressions

In addition to the expressions defined in ForwardContainer, the following expressions must be valid.

Name	Expression	Type requirements	Return type
Beginning of range	a.rbegin()		reverse_iterator if a is mutable, const_reverse_iterator otherwise [1]
End of range	a.rend()		reverse_iterator if a is mutable, const_reverse_iterator otherwise [1]

Expression Semantics

Semantics of an expression is defined only where it is not defined in ForwardContainer, or where there is additional information.

Name	Expression	Precondition	Semantics	Postcondition
Beginning of reverse range	a.rbegin()		Equivalent to X::reverse_iterator(a.end()).	a.rbegin() is dereferenceable or past-the-end. It is past-the-end if and only if a.size() == 0.
End of reverse range	a.rend()		Equivalent to X::reverse_iterator(a.begin()).	a.end() is past-the-end.

Complexity Guarantee(s)

The run-time complexity of rbegin() and rend() is amortized constant time.

Invariants

Valid range	[a.rbegin(), a.rend()) is a valid range.
Equivalence of ranges	The distance from a.begin() to a.end() is the same as the distance from a.rbegin() to a.rend().

Type(s) Modeling this Concept

• Vector
• List
• Deque

Notes

[1] A Container's iterator type and const iterator type may be the same type: a container need not provide mutable iterators.
It follows from this that the reverse iterator type and the const reverse iterator type may also be the same.

See Also

The Iterators, BidirectionalIterator, Sequence