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Difference between revisions of "cpp/iterator/weakly incrementable"

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< cpp‎ | iterator
m (fmt)
(Removed the definition of “integer-like type”, it is in a new page now.)
 
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where {{c|/*is-signed-integer-like*/<I>}} is {{c|true}} if and only if {{tt|I}} is a signed-integer-like type (see below).
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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}}.
 
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}}.
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===Semantic requirements===
 
===Semantic requirements===
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{{tt|I}} models {{tt|std::weakly_incrementable}} only if, for an object {{tt|i}} of type {{tt|I}}:
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For an object {{c|i}} of type {{tt|I}}, {{tt|I}} models {{tt|std::weakly_incrementable}} only if all following conditions are satisfied:
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* The expressions {{c|++i}} and {{c|i++}} have the same domain,
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* The expressions {{c|++i}} and {{c|i++}} have the same domain.
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* If {{tt|i}} is incrementable, then both {{c|++i}} and {{c|i++}} advance {{tt|i}}, and
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* If {{c|i}} is incrementable, then both {{c|++i}} and {{c|i++}} advance {{c|i}}.
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* If {{tt|i}} is incrementable, then {{c|1=std::addressof(++i) == std::addressof(i)}}.
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* If {{c|i}} is incrementable, then {{c|1=std::addressof(++i) == std::addressof(i)}}.
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===Integer-like types===
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An integer-like type is an (possibly cv-qualified) integer type (except for ''cv'' {{c|bool}}) or an implementation-provided (not user-provided) class that behaves like an integer type, including all operators, implicit conversions, and {{lc|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.
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===Defect reports===
 
===Defect reports===
 
{{dr list begin}}
 
{{dr list begin}}
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{{dr list item|wg=lwg|dr=3467|std=C++20|before={{c|bool}} was considered as an integer-like type|after=excluded}}
 
 
{{dr list item|paper=P2325R3|std=C++20|before={{lconcept|default_initializable}} was required|after=not required}}
 
{{dr list item|paper=P2325R3|std=C++20|before={{lconcept|default_initializable}} was required|after=not required}}
 
{{dr list end}}
 
{{dr list end}}

Latest revision as of 18:40, 9 September 2024

 
C++
 
Iterator library
Iterator concepts
(C++20)
(C++20)
weakly_incrementable
(C++20)
(C++20)
(C++20)(C++20)
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
(C++20)
(C++20)
(C++20)
Utilities
(C++20)
Iterator adaptors
Range access
(C++11)(C++14)
(C++14)(C++14)  
(C++11)(C++14)
(C++14)(C++14)  
(C++17)(C++20)
(C++17)
(C++17)
 
Defined in header <iterator>
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

        };
 (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) [edit]
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