24 Ranges library [ranges]

24.7 Range adaptors [range.adaptors]

24.7.13 Common view [range.common]

24.7.13.3 views​::​common [range.common.adaptor]

The name views​::​common denotes a range adaptor object ([range.adaptor.object]).
For some subexpression E, the expression views​::​common(E) is expression-equivalent to:
  • views​::​all(E), if decltype((E)) models common_­range and views​::​all(E) is a well-formed expression.
  • Otherwise, common_­view{E}.