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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.