设计模式-行为-访问者

#pragma once

#ifndef VISITOR_H 

#define VISITOR_H 

class Visitor; 

class Element 
{ 
public: 
  virtual ~Element(){} 
  virtual void Accept(Visitor &rVisitor) = 0; 
protected: 
  Element(){} 
}; 

class ConcreateElementA : public Element 
{ 
public: 
  virtual ~ConcreateElementA() {} 
  virtual void Accept(Visitor &rVisitor); 
}; 

class ConcreateElementB : public Element 
{ 
public: 
  virtual ~ConcreateElementB() {} 
  virtual void Accept(Visitor &rVisitor); 
}; 

class Visitor 
{ 
public: 
  virtual ~Visitor(){} 
  virtual void VisitConcreateElementA(ConcreateElementA *pConcreateElementA) = 0; 
  virtual void VisitConcreateElementB(ConcreateElementB *pConcreateElementB) = 0; 

protected: 
  Visitor(){} 
}; 

class ConcreateVisitorA : public Visitor 
{ 
public: 
  virtual ~ConcreateVisitorA(){} 
  virtual void VisitConcreateElementA(ConcreateElementA *pConcreateElementA); 
  virtual void VisitConcreateElementB(ConcreateElementB *pConcreateElementB); 
}; 

class ConcreateVisitorB : public Visitor 
{ 
public: 
  virtual ~ConcreateVisitorB(){}
  virtual void VisitConcreateElementA(ConcreateElementA *pConcreateElementA); 
  virtual void VisitConcreateElementB(ConcreateElementB *pConcreateElementB); 
}; 

#endif

#include "StdAfx.h"
#include "visitor_impl.h"

#include <iostream> 

void ConcreateElementA::Accept(Visitor &rVisitor) 
{ 
  rVisitor.VisitConcreateElementA(this); 
} 

void ConcreateElementB::Accept(Visitor &rVisitor) 
{ 
  rVisitor.VisitConcreateElementB(this); 
} 

void ConcreateVisitorA::VisitConcreateElementA(ConcreateElementA *pConcreateElementA)
{ 
  std::cout << "VisitConcreateElementA By ConcreateVisitorA\n"; 
} 

void ConcreateVisitorA::VisitConcreateElementB(ConcreateElementB *pConcreateElementA) 
{ 
  std::cout << "VisitConcreateElementB By ConcreateVisitorA\n"; 
} 

void ConcreateVisitorB::VisitConcreateElementA(ConcreateElementA *pConcreateElementA) 
{ 
  std::cout << "VisitConcreateElementA By ConcreateVisitorB\n"; 
} 

void ConcreateVisitorB::VisitConcreateElementB(ConcreateElementB *pConcreateElementA) 
{ 
  std::cout << "VisitConcreateElementB By ConcreateVisitorB\n"; 
}

// Visitor.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"

#include "visitor_impl.h"
#include <stdlib.h>
//表示一个作用于某对象结构中的各元素的操作.它使你可以在不改变各元素的类的前提下定义作用于这些元素的新操作. 
//实现了"双分派"的概念，一个操作(Accept)既依赖于执行操作的具体类型(Element *)有依赖于操作传入参数的类型(Visitor *)
int _tmain(int argc, _TCHAR* argv[])
{
  Visitor *pVisitor1 = new ConcreateVisitorA(); 
  Visitor *pVisitor2 = new ConcreateVisitorB();

  Element *pElementA = new ConcreateElementA(); 
  pElementA->Accept(*pVisitor1); 
  pElementA->Accept(*pVisitor2); 

  Element *pElementB = new ConcreateElementB();
  pElementB->Accept(*pVisitor1); 
  pElementB->Accept(*pVisitor2); 

  delete pElementA; 
  delete pElementB; 
  delete pVisitor1;
  delete pVisitor2;

  system("pause");

  return 0;
}