#include <iostream>
#include <string>
using namespace std;

// 1. Add an accept(Visitor) method to the "element" hierarchy
class Element{
  public:
    virtual void accept(class Visitor &v) = 0;
};

class This: public Element{
  public:
     void accept(Visitor &v);
    string thiss(){
        return "This";
    }
};

class That: public Element{
  public:
    void accept(Visitor &v);
    string that(){
        return "That";
    }
};

class TheOther: public Element{
  public:
    void accept(Visitor &v);
    string theOther(){
        return "TheOther";
    }
};

// 2. Create a "visitor" base class w/ a visit() method for every "element" type
class Visitor{
  public:
    virtual void visit(This *e) = 0;
    virtual void visit(That *e) = 0;
    virtual void visit(TheOther *e) = 0;
};

void This::accept(Visitor &v){
	v.visit(this);
}

void That::accept(Visitor &v){
	v.visit(this);
}

void TheOther::accept(Visitor &v){
	v.visit(this);
}

// 3. Create a "visitor" derived class for each "operation" to do on "elements"
class UpVisitor: public Visitor{
    void visit(This *e){
        cout << "do Up on " + e->thiss() << '\n';
    }
    void visit(That *e){
        cout << "do Up on " + e->that() << '\n';
    }
    void visit(TheOther *e){
        cout << "do Up on " + e->theOther() << '\n';
    }
};

class DownVisitor: public Visitor{
    void visit(This *e){
    cout << "do Down on " + e->thiss() << '\n';
	}
	void visit(That *e){
        cout << "do Down on " + e->that() << '\n';
    }
    void visit(TheOther *e){
        cout << "do Down on " + e->theOther() << '\n';
    }
};

int main(){
  Element *list[] = {
    new This(), new That(), new TheOther()
  };
  UpVisitor up; 	// 4. Client creates
  DownVisitor down; //    "visitor" objects
  for (int i = 0; i < 3; i++) list[i]->accept(up);
  for (int i = 0; i < 3; i++) list[i]->accept(down);
}