Forward Sequence

Description

A Forward Sequence is an MPL concept representing a compile-time sequence of elements. Sequence elements are types, and are accessible through Iterators. The begin and end metafunctions provide iterators delimiting the range of the sequence elements. A sequence guarantees that its elements are arranged in a definite, but possibly unspecified, order. Every MPL sequence is a Forward Sequence.

Definitions

The size of a sequence is the number of elements it contains. The size is a nonnegative number.
A sequence is empty if its size is zero.

Expression requirements

For any Forward Sequence s the following expressions must be valid:

Expression	Type	Complexity
`begin<s>::type`	Forward Iterator	Amortized constant time
`end<s>::type`	Forward Iterator	Amortized constant time
`size<s>::type`	Integral Constant	Unspecified
`empty<s>::type`	Boolean Integral Constant	Constant time
`front<s>::type`	Any type	Amortized constant time

Expression semantics

Expression	Semantics
`begin<s>::type`	An iterator to the first element of the sequence; see `begin`.
`end<s>::type`	A past-the-end iterator to the sequence; see `end`.
`size<s>::type`	The size of the sequence; see `size`.
`empty<s>::type`	A boolean Integral Constant `c` such that `c::value == true` if and only if the sequence is empty; see `empty`.
`front<s>::type`	The first element in the sequence; see `front`.

Invariants

For any Forward Sequence s the following invariants always hold:

[begin<s>::type, end<s>::type) is always a valid range.
An algorithm that iterates through the range [begin<s>::type, end<s>::type) will pass through every element of s exactly once.
begin<s>::type is identical to end<s>::type if and only if s is empty.
Two different iterations through s will access its elements in the same order.