23 Iterators library [iterators]

23.5 Iterator adaptors [predef.iterators]

23.5.3 Move iterators and sentinels [move.iterators]

23.5.3.4 Conversion [move.iter.op.conv]

constexpr Iterator base() const &;
Constraints: Iterator satisfies copy_­constructible.
Expects: Iterator models copy_­constructible.
Returns: current.
constexpr Iterator base() &&;
Returns: std​::​move(current).