27 Iterators library [iterators]

27.5 Iterator adaptors [predef.iterators]

27.5.1 Reverse iterators [reverse.iterators]

27.5.1.3 reverse_­iterator operations [reverse.iter.ops]

27.5.1.3.7 operator-- [reverse.iter.op--]

constexpr reverse_iterator& operator--();

constexpr reverse_iterator operator--(int);

reverse_iterator tmp = *this;
++current;
return tmp;