Random Access Sequence

Description

A Random Access Sequence is a Bidirectional Sequence whose iterators model Random Access Iterator. It guarantees constant time access to arbitrary sequence elements.

Refinement of

Bidirectional Sequence

Notation

s: A Random Access Sequence
S: A Random Access Sequence type
N: An integral constant
o: An arbitrary object
e: A Sequence element

Valid Expressions

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

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

Result Type Expressions

Expression	Compile Time Complexity
`result_of::begin<S>::type`	Amortized constant time
`result_of::end<S>::type`	Amortized constant time
`result_of::at<S, N>::type`	Amortized constant time
`result_of::value_at<S, N>::type`	Amortized constant time

note result_of::at<S, N> returns the actual type returned by at<N>(s). In most cases, this is a reference. Hence, there is no way to know the exact element type using result_of::at<S, N>.The element at N may actually be a reference to begin with. For this purpose, you can use result_of::value_at<S, N>.

Expression Semantics

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

Expression	Semantics
`at<N>(s)`	The Nth element from the beginning of the sequence; see `at`.

Models

std::pair
boost::array
vector
iterator_range (where adapted sequence is a Random Access Sequence)
transform_view (where adapted sequence is a Random Access Sequence)
reverse_view