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

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< cpp‎ | iterator
m (→‎Integer-like types: English)
m (→‎Integer-like types: Integer-classes are not user provided if I get it right...)
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===Integer-like types===
 
===Integer-like types===
−
An integer-like type is an (possibly cv-qualified) integer type (except for ''cv'' {{c|bool}}) or a class that behaves like an integer type, including all operators, implicit conversions, and {{lc|std::numeric_limits}} specializations. If an integer-like type only represents non-negative values, it is unsigned-integer-like, otherwise it is signed-integer-like.
+
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 only represents non-negative values, it is unsigned-integer-like, otherwise it is signed-integer-like.
  
 
===Defect reports===
 
===Defect reports===

Revision as of 00:35, 25 July 2021

 
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)

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 given only object i of type I:

  • 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)

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 only represents 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) [edit]
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