Difference between revisions of "cpp/iterator/weakly incrementable"
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{{dcl begin}} | {{dcl begin}} | ||
{{dcl header|iterator|since=c++20}} | {{dcl header|iterator|since=c++20}} | ||
| − | {{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}} | ||
| − | |||
| − | 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 {{lc|std::equality_comparable}}. | + | For the definition of {{c/core|/*is-signed-integer-like*/}}, see {{rlpi|is-integer-like}}{{sep}}. |
| + | |||
| + | This concept specifies requirements on types that can be incremented with the pre- and post-increment operators, but those increment operations are not necessarily [[cpp/concepts#Equality preservation|equality-preserving]], and the type itself is not required to be {{lc|std::equality_comparable}}. | ||
For {{tt|std::weakly_incrementable}} types, {{c|1=a == b}} does not imply that {{c|1=++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 {{lc|std::istream_iterator}}. | For {{tt|std::weakly_incrementable}} types, {{c|1=a == b}} does not imply that {{c|1=++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 {{lc|std::istream_iterator}}. | ||
===Semantic requirements=== | ===Semantic requirements=== | ||
| − | {{ | + | For an object {{c|i}} of type {{tt|I}}, {{tt|I}} models {{tt|std::weakly_incrementable}} only if all following conditions are satisfied: |
| − | * The expressions {{c|++i}} and {{c|i++}} have the same domain | + | * The expressions {{c|++i}} and {{c|i++}} have the same domain. |
| − | * If {{ | + | * If {{c|i}} is incrementable, then both {{c|++i}} and {{c|i++}} advance {{c|i}}. |
| − | * If {{ | + | * If {{c|i}} is incrementable, then {{c|1=std::addressof(++i) == std::addressof(i)}}. |
| − | + | ||
| − | + | ||
| − | + | ||
===Defect reports=== | ===Defect reports=== | ||
{{dr list begin}} | {{dr list begin}} | ||
| − | {{dr list item| | + | {{dr list item|paper=P2325R3|std=C++20|before={{lconcept|default_initializable}} was required|after=not required}} |
{{dr list end}} | {{dr list end}} | ||
| − | === See also === | + | ===See also=== |
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/iterator/dsc | + | {{dsc inc|cpp/iterator/dsc incrementable}} |
{{dsc end}} | {{dsc end}} | ||
| − | {{langlinks|es|ja|ru|zh}} | + | {{langlinks|de|es|ja|ru|zh}} |
Latest revision as of 18:40, 9 September 2024
| Defined in header <iterator>
|
||
| template< class I > concept weakly_incrementable = |
(since C++20) | |
For the definition of /*is-signed-integer-like*/, see is-integer-like .
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.
[edit] Semantic requirements
For an object i of type I, I models std::weakly_incrementable only if all following conditions are satisfied:
- The expressions ++i and i++ have the same domain.
- If i is incrementable, then both ++i and i++ advance i.
- If i is incrementable, then std::addressof(++i) == std::addressof(i).
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2325R3 | C++20 | default_initializable was required
|
not required |
[edit] 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) |
