std::sentinel_for
| Defined in header <iterator>
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||
| template< class S, class I > concept sentinel_for = |
(since C++20) | |
The sentinel_for concept specifies the relationship between an input_or_output_iterator type and a semiregular type whose values denote a range. The exposition-only concept __WeaklyEqualityComparableWith is described in equality_comparable.
Semantic requirements
Let s and i be values of type S and I, respectively, such that [i, s) denotes a range. sentinel_for<S, I> is modeled only if:
- i == s is well-defined.
- If bool(i != s) then
iis dereferenceable and[++i,s)denotes a range. - std::assignable_from<I&, S> is either modeled or not satisfied.
The domain of == can change over time. Given an iterator i and sentinel s such that [i, s) denotes a range and i != s, [i, s) is not required to continue to denote a range after incrementing any iterator equal to i (and so i == s is no longer required to be well-defined after such an increment).
Notes
A sentinel type and its corresponding iterator type are not required to model equality_comparable_with, because the sentinel type may not be comparable with itself, and they are not required to have a common reference type.
It has been permitted to use a sentinel type different from the iterator type in the range-based for loop since C++17.
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3453 | C++20 | semantic requirements for sentinel_for were too loose for ranges::advance
|
strengthened |