std::weakly_incrementable

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
        };

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.

See also