std::sized_sentinel_for, std::disable_sized_sentinel_for
| Defined in header <iterator>
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| template< class S, class I > concept sized_sentinel_for = |
(1) | (since C++20) |
| template< class S, class I > inline constexpr bool disable_sized_sentinel_for = false; |
(2) | (since C++20) |
sized_sentinel_for concept specifies that an object of the iterator type I and an object of the sentinel type S can be subtracted to compute the distance between them in constant time.disable_sized_sentinel_for variable template can be used to prevent iterators and sentinels that can be subtracted but do not actually model sized_sentinel_for from satisfying the concept.disable_sized_sentinel_for for cv-unqualified non-array object type S and I, as long as at least one of which is a program-defined type. Such specializations are usable in constant expressions and have type const bool.Semantic requirements
Let i be an iterator of type I, and s a sentinel of type S such that [i, s) denotes a range. Let n be the smallest number of applications of ++i necessary to make bool(i == s) be true. I and S model sized_sentinel_for<S, I> only if all following conditions are satisfied:
- If n is representable by std::iter_difference_t<I>, then s - i is well-defined and equals n.
- If -n is representable by std::iter_difference_t<I>, then i - s is well-defined and equals -n.
Equality preservation
Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).
Implicit expression variations
A requires expression that uses an expression that is non-modifying for some constant lvalue operand also requires implicit expression variations.
See also
| (C++20) |
specifies that a range knows its size in constant time (concept) |
| (C++20) |
returns an integer equal to the size of a range (customization point object) |