Difference between revisions of "cpp/iterator/weakly incrementable"
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{{dcl|since=c++20|1= | {{dcl|since=c++20|1= | ||
template< class I > | template< class I > | ||
| − | + | concept weakly_incrementable = | |
| − | + | std::movable<I> && | |
| − | + | requires(I i) { | |
| − | + | typename std::iter_difference_t<I>; | |
| − | + | requires /*is-signed-integer-like*/<std::iter_difference_t<I>>; | |
| − | + | { ++i } -> std::same_as<I&>; // not required to be equality-preserving | |
| − | + | i++; // not required to be equality-preserving | |
| − | + | }; | |
}} | }} | ||
{{dcl end}} | {{dcl end}} | ||
Revision as of 23:52, 1 October 2023
| Defined in header <iterator>
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| template< class I > concept weakly_incrementable = |
(since C++20) | |
where /*is-signed-integer-like*/<I> is true if and only if I is a signed-integer-like type (see below).
This concept specifies requirements on types that can be incremented with the pre- and post-increment operators, but those increment operations are not necessarily equality-preserving, and the type itself is not required to be std::equality_comparable.
For std::weakly_incrementable types, a == b does not imply that ++a == ++b. Algorithms on weakly incrementable types must be single-pass algorithms. These algorithms can be used with istreams as the source of the input data through std::istream_iterator.
Contents |
Semantic requirements
I models std::weakly_incrementable only if, for an object i of type I:
- The expressions ++i and i++ have the same domain,
- If
iis incrementable, then both ++i and i++ advancei, and - If
iis incrementable, then std::addressof(++i) == std::addressof(i).
Integer-like types
An integer-like type is an (possibly cv-qualified) integer type (except for cv bool) or an implementation-provided (not user-provided) class that behaves like an integer type, including all operators, implicit conversions, and std::numeric_limits specializations. If an integer-like type represents only non-negative values, it is unsigned-integer-like, otherwise it is signed-integer-like.
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 3467 | C++20 | bool was considered as an integer-like type | excluded |
| P2325R3 | C++20 | default_initializable was required
|
not required |
See also
| (C++20) |
specifies that the increment operation on a weakly_incrementable type is equality-preserving and that the type is equality_comparable (concept) |
