cpp/ranges/join view/sentinel

The return type of when either of the underlying ranges ( or ) is not a, or when the parent  is not a.

If is not a simple view,  is true for sentinels returned from the const overloads, and false otherwise. If is a simple view,  is true.

The name of this class template (shown here as ) is unspecified.

Typical implementation holds only one data member: a sentinel obtained from (possibly const-qualified).