The random_access_iterator concept adds support for
constant-time advancement with +=, +, -=, and -,
as well as the computation of distance in constant time with -.

Random access iterators also support array notation via subscripting.

template<class I> concept random_access_iterator = bidirectional_iterator<I> && derived_from<ITER_CONCEPT(I), random_access_iterator_tag> && totally_ordered<I> && sized_sentinel_for<I, I> && requires(I i, const I j, const iter_difference_t<I> n) { { i += n } -> same_as<I&>; { j + n } -> same_as<I>; { n + j } -> same_as<I>; { i -= n } -> same_as<I&>; { j - n } -> same_as<I>; { j[n] } -> same_as<iter_reference_t<I>>; };

Let a and b be valid iterators of type I
such that b is reachable from a
after n applications of ++a,
let D be iter_difference_t<I>,
and let n denote a value of type D.

I models random_access_iterator only if

- (a += n) is equal to b.
- addressof(a += n) is equal to addressof(a).
- (a + n) is equal to (a += n).
- For any two positive values x and y of type D, if (a + D(x + y)) is valid, then (a + D(x + y)) is equal to ((a + x) + y).
- (a + D(0)) is equal to a.
- If (a + D(n - 1)) is valid, then (a + n) is equal to [](I c){ return ++c; }(a + D(n - 1)).
- (b += -n) is equal to a.
- (b -= n) is equal to a.
- addressof(b -= n) is equal to addressof(b).
- (b - n) is equal to (b -= n).
- If b is dereferenceable, then a[n] is valid and is equal to *b.
- bool(a <= b) is true.