Recursive Implementations 5: Display without Iterators

  class PrintValue // function class to pass to Traverse()
  {
  public:
    PrintValue (std::ostream& os, char ofc) : os_(os), ofc_(ofc) // constructor
    {}
    void operator() (const Node* n) const // evaluation operator
    {
      if (ofc_ == '\0')
        os_ << n->value_; 
      else
        os_ << n->value_ << ofc_;
    }
  private:
    std::ostream& os_;  // stored reference to os
    char          ofc_; // stored output formatting character
  };

  void  Display (std::ostream& os, char ofc) const
  {
    PrintValue printval(os,ofc); // create function object
    Traverse (printval);         // call Traverse with f = printval
  }