C++设计模式——访问者模式

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

class concreteElementA;
class concreteElementB;
class visitor
{
public:
visitor(){};
virtual ~visitor(){};
virtual void visitConcreteElementA(concreteElementA* pConcreteElementA) = 0;
virtual void visitConcreteElementB(concreteElementB* pConcreteElementB) = 0;
};

class concreteVisitor1 : public visitor
{
public:
concreteVisitor1(){};
~concreteVisitor1(){};
virtual void visitConcreteElementA(concreteElementA* pConcreteElementA)
{
cout << "concreteElementA被concreteVisitor1访问" << endl;
}
virtual void visitConcreteElementB(concreteElementB* pConcreteElementB)
{
cout << "concreteElementB被concreteVisitor1访问" << endl;
}
};

class concreteVisitor2 : public visitor
{
public:
concreteVisitor2(){};
~concreteVisitor2(){};
virtual void visitConcreteElementA(concreteElementA* pConcreteElementA)
{
cout << "concreteElementA被concreteVisitor2访问" << endl;
}
virtual void visitConcreteElementB(concreteElementB* pConcreteElementB)
{
cout << "concreteElementB被concreteVisitor2访问" << endl;
}
};

class element
{
public:
element(){};
virtual ~element(){};
virtual void accept(visitor* pVisitor) = 0;
};

class concreteElementA : public element
{
public:
concreteElementA(){};
~concreteElementA(){};
// 充分利用双分派技术，实现处理与数据结构的分离
virtual void accept(visitor* pVisitor)
{
if (NULL != pVisitor)
{
pVisitor->visitConcreteElementA(this);
}
}
// 其他的相关方法
void operationA()
{
cout << "具体元素A的其他相关方法" << endl;
}
};
class concreteElementB : public element
{
public:
concreteElementB(){};
~concreteElementB(){};
// 充分利用双分派技术，实现处理与数据结构的分离
virtual void accept(visitor* pVisitor)
{
if (NULL != pVisitor)
{
pVisitor->visitConcreteElementB(this);
}
}
// 其他的相关方法
void operationB()
{
cout << "具体元素B的其他相关方法" << endl;
}
};

class objectStructure
{
public:
void attach(element* pElement)
{
m_list.push_back(pElement);
}
void detach(element* pElement)
{
m_list.remove(pElement);
}
void accept(visitor* pVisitor)
{
list<element*>::iterator Iter;
for (Iter = m_list.begin(); Iter != m_list.end(); ++Iter)
{
if (NULL != *Iter)
{
(*Iter)->accept(pVisitor);
}
}
}
int  GetSize()
{
return m_list.size();
}
private:
list<element*>  m_list;
};

void freePtr(void* vptr)
{
if (NULL != vptr)
{
delete vptr;
vptr = NULL;
}
}
int main(int argc, char* argv[])
{
objectStructure* pObject = new objectStructure();
if (NULL != pObject)
{
element* pElementA = new concreteElementA();
element* pElementB = new concreteElementB();
pObject->attach(pElementA);
pObject->attach(pElementB);
concreteVisitor1* pVisitor1 = NULL;
pVisitor1 = new concreteVisitor1();
concreteVisitor2* pVisitor2 = NULL;
pVisitor2 = new concreteVisitor2();
pObject->accept(pVisitor1);
pObject->accept(pVisitor2);
system("pause");
freePtr(pVisitor2);
freePtr(pVisitor1);
freePtr(pElementB);
freePtr(pElementA);
freePtr(pObject);
}
return 0;
}