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Reversible Container


Category: containers	Component type: concept

Description

A Reversible Container is a Forward Container whose iterators are Bidirectional Iterators. It allows backwards iteration through the container.

Refinement of

Forward Container

Associated types

Two new types are introduced. In addition, the iterator type and the const iterator type must satisfy a more stringent requirement than for a Forward Container. The iterator and reverse iterator types must be Bidirectional Iterators, not merely Forward Iterators.

Reverse iterator type	`X::reverse_iterator`	A Reverse Iterator adaptor whose base iterator type is the container's iterator type. Incrementing an object of type `reverse_iterator` moves backwards through the container: the Reverse Iterator adaptor maps `operator++` to `operator--`.
Const reverse iterator type	`X::const_reverse_iterator`	A Reverse Iterator 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 Forward Container, 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 Forward Container, 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 guarantees

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()`.

Models

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.