26 Ranges library [ranges]

26.3 Range access [range.access]

26.3.4 ranges​::​cbegin [range.access.cbegin]

The name ranges​::​cbegin denotes a customization point object ([customization.point.object]).
Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.
  • If E is an rvalue and enable_borrowed_range<remove_cv_t<T>> is false, ranges​::​cbegin(E) is ill-formed.
  • Otherwise, let U be ranges​::​begin(possibly-const-range(t)).
    ranges​::​cbegin(E) is expression-equivalent to const_iterator<decltype(U)>(U).
[Note 1: 
Whenever ranges​::​cbegin(E) is a valid expression, its type models input_or_output_iterator and constant-iterator.
— end note]