< cpp‎ | iterator
Iterator library
Iterator concepts
Iterator primitives
Iterator adaptors
Stream iterators
Iterator customization points
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Range access
Defined in header <iterator>
template<class I>

    concept incrementable =
        std::regular<I> &&
        std::weakly_incrementable<I> &&
        requires(I i) {
            { i++ } -> std::same_as<I>;

(since C++20)

Additionally, if any two objects a and b of type I are incrementable, I satisfies std::incrementable only if

  • bool(a == b) implies bool(a++ == b), and
  • bool(a == b) implies bool(((void)a++, a) == ++b)

This concept specifies requirements on types that can be incremented with the pre- and post-increment operators, whose increment operations are equality-preserving, and the type is std::equality_comparable.

Unlike with std::weakly_incrementable, which only support single-pass algorithms, multi-pass one-directional algorithms can be used with types that model std::incrementable.

[edit] Equality preservation

An expression is equality preserving if it results in equal outputs given equal inputs.

  • The inputs to an expression consist of its operands.
  • The outputs of an expression consist of its result and all operands modified by the expression (if any).

Every expression required to be equality preserving is further required to be stable: two evaluations of such an expression with the same input objects must have equal outputs absent any explicit intervening modification of those input objects.

Unless noted otherwise, every expression used in a requires-expression is required to be equality preserving and stable, and the evaluation of the expression may only modify its non-constant operands. Operands that are constant must not be modified.

[edit] See also

specifies that a semiregular type can be incremented with pre- and post-increment operators
(concept) [edit]
specifies that a type is the same as another type
(concept) [edit]