26 Ranges library [ranges]

26.6 Range factories [range.factories]

26.6.3 Single view [range.single] Overview [range.single.overview]

single_view produces a view that contains exactly one element of a specified value.
The name views​::​single denotes a customization point object ([customization.point.object]).
Given a subexpression E, the expression views​::​single(E) is expression-equivalent to single_view<decay_t<decltype((E))>>(E).
[Example 1: for (int i : views::single(4)) cout << i; // prints 4 — end example]