Boost C++ Libraries - Bidirectional Sequence

A Bidirectional Sequence is a Forward Sequence whose iterators model Bidirectional Iterator.

Notation

In addition to the requirements defined in Forward Sequence, for any Bidirectional Sequence the following must be met:

Expression	Return type	Type Requirements	Runtime Complexity
`begin(s)`	Bidirectional Iterator		Constant
`end(s)`	Bidirectional Iterator		Constant
`back(s)`	Any type		Constant
`back(s) = o`	Any type	`s` is mutable and `e = o`, where `e` is the first element in the sequence, is a valid expression.	Constant

The semantics of an expression are defined only where they differ from, or are not defined in Forward Sequence.

Expression	Semantics
`back(s)`	The last element in the sequence; see `back`.