Get a range of preorder iterators for a given range template <class R> auto preorder_range(R & x) (1) template <class R> auto preorder_range(const R & x) (2) (1) template <class R> auto preorder_range(R & x) Mutable variant Parameters R & x (2) template <class R> auto preorder_range(const R & x) Const variant Parameters const R & x