24 Ranges library [ranges]

If E is an rvalue and enable_­borrowed_­range<remove_­cv_­t<T>> is false, ranges​::​rbegin(E) is ill-formed.

Otherwise, if T is an array type ([basic.compound]) and remove_­all_­extents_­t<T> is an incomplete type, ranges​::​rbegin(E) is ill-formed with no diagnostic required.

Otherwise, if decay-copy(t.rbegin()) is a valid expression whose type models input_­or_­output_­iterator, ranges​::​rbegin(E) is expression-equivalent to decay-copy(t.rbegin()).

Otherwise, if T is a class or enumeration type and decay-copy(rbegin(t)) is a valid expression whose type models input_­or_­output_­iterator with overload resolution performed in a context in which unqualified lookup for rbegin finds only the declarations

void rbegin(auto&) = delete;
void rbegin(const auto&) = delete;

then ranges​::​rbegin(E) is expression-equivalent to decay-copy(rbegin(t)) with overload resolution performed in the above context.

Otherwise, if both ranges​::​begin(t) and ranges​::​end(t) are valid expressions of the same type which models bidirectional_­iterator ([iterator.concept.bidir]), ranges​::​rbegin(E) is expression-equivalent to make_­reverse_­iterator(ranges​::​end(t)).

Otherwise, ranges​::​rbegin(E) is ill-formed.