Visitor模式

不破坏类封装的前提下，添加新的操作

你中有我，我中有你么？

Visitor.h

#ifndef _VISITOR_H

#define _VISITOR_H

#include

using namespace std;

class Element;

class Visitor

{

public:

virtual ~Visitor() {

}

virtual void VisitConcreteElementA(Element* element)=0;

virtual void VisitConcreteElementB(Element* element)=0;

protected:

Visitor() {

}

};

class Element

{

public:

virtual ~Element() {

}

virtual void Accept(Visitor* vis)=0;

protected:

Element() {

}

};

class ConcreteElementA : public Element

{

public:

ConcreteElementA() {

}

~ConcreteElementA() {

}

void Accept(Visitor* vis) {

cout << "ConcreteElementA" << endl;

vis->VisitConcreteElementA(this);

}

};

class ConcreteElementB : public Element

{

public:

ConcreteElementB() {

}

~ConcreteElementB() {

}

void Accept(Visitor* vis) {

cout << "ConcreteElementB" << endl;

vis->VisitConcreteElementB(this);

}

};

class ConcreteVisitorA : public Visitor

{

public:

ConcreteVisitorA() {

}

~ConcreteVisitorA() {

}

void VisitConcreteElementA(Element* element) {

cout << "VisitConcreteElementA:A" << endl;

}

void VisitConcreteElementB(Element* element) {

cout << "VisitConcreteElementA:B" << endl;

}

};

class ConcreteVisitorB : public Visitor

{

public:

ConcreteVisitorB() {

}

~ConcreteVisitorB() {

}

void VisitConcreteElementA(Element* element) {

cout << "VisitConcreteElementB:A" << endl;

}

void VisitConcreteElementB(Element* element) {

cout << "VisitConcreteElementB:B" << endl;

}

};

#endif // _VISITOR_H

Visitor.cpp

#include "Visitor.h"

int main()

{

Visitor* vis = new ConcreteVisitorA();

Element* element = new ConcreteElementA();

element->Accept(vis);

return 0;

}

编译:make Visitor