26 Ranges library [ranges]

26.7 Range adaptors [range.adaptors]

26.7.18 Counted view [range.counted]

A counted view presents a view of the elements of the counted range ([iterator.requirements.general]) for an iterator i and non-negative integer n.
The name views​::​counted denotes a customization point object ([customization.point.object]).
Let E and F be expressions, let T be decay_t<decltype((E))>, and let D be iter_difference_t<T>.
If decltype((F)) does not model convertible_to<D>, views​::​counted(E, F) is ill-formed.
[Note 1: 
This case can result in substitution failure when views​::​counted(E, F) appears in the immediate context of a template instantiation.
— end note]
Otherwise, views​::​counted(E, F) is expression-equivalent to:
  • If T models contiguous_iterator, then span(to_address(E), static_cast<size_t>(static_-
  • Otherwise, if T models random_access_iterator, then subrange(E, E + static_cast<D>(F)), except that E is evaluated only once.
  • Otherwise, subrange(counted_iterator(E, F), default_sentinel).