Recursive Implementations 4: Traverse without Iterators?

protected:
  template < class F >  // function class
  static void RTraverse (Node* n, F f)
  // classic inorder traversal; apply function object f  to each element
  {
    if (n == 0) return;
    RTraverse(n->lchild_, f);
    f(n); // function object call
    RTraverse(n->rchild_, f);
  }
  ...
public:
  template < class F >
  void Traverse (F f) { RTraverse(root_,f); }
  ...