std::weakly_incrementable

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

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)

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

See also

incrementable (C++20)

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