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std::weakly_incrementable

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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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