NAME¶

std::weakly_incrementable - std::weakly_incrementable

Synopsis¶

Defined in header <iterator>
template<class I>

concept weakly_incrementable =
std::movable<I> &&
requires(I i) { (since
typename std::iter_difference_t<I>; C++20)
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

};

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.

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 i is incrementable, then both ++i and i++ advance i, and
* 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 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¶

incrementable specifies that the increment operation on a weakly_incrementable type
(C++20) is equality-preserving and that the type is equality_comparable
(concept)