visitor 访问者模式

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

class element;
class visitor
{
public:
    visitor(string name): _name(name){}
    virtual ~visitor(){}
    virtual void visit_concrete_elementA(element *) =0;
    virtual void visit_concrete_elementB(element *) =0;
    string name(){return _name;}
protected:
    visitor(){}
    string _name;
};

class element
{
public:
    virtual ~element(){}
    virtual void accept(visitor *vis) =0;
protected:
    element(){}
};
class concrete_visitorA : public visitor
{
public:
    concrete_visitorA(string name):visitor(name){}
    void visit_concrete_elementA(element *ele)
    {
        cout<<"visitorA visit elementA... "<<endl;
        ele->accept(this);
    }
    void visit_concrete_elementB(element *ele)
    {
        cout<<"visitorA visit elementB... "<<endl;
        ele->accept(this);
    }
};
class concrete_visitorB : public visitor
{
public:
    concrete_visitorB(string name):visitor(name){}
    void visit_concrete_elementA(element *ele)
    {
        cout<<"visitorB visit elementA... "<<endl;
        ele->accept(this);
    }
    void visit_concrete_elementB(element *ele)
    {
        cout<<"visitorB visit elementA... "<<endl;
        ele->accept(this);
    }
};


class concrete_elementA : public element
{
public:
    void accept(visitor *vis)
    {
        cout<<"elementA accepted... :"<< vis->name()<<endl;
    }
};

class concrete_elementB : public element
{
public:
    void accept(visitor *vis)
    {
        cout<<"elementA accepted... :"<< vis->name()<<endl;
    }
};

int main()
{
    visitor *vA = new concrete_visitorA(string("A"));
    visitor *vB = new concrete_visitorB(string("B"));
    element *eA = new concrete_elementA;
    element *eB = new concrete_elementB;
    
    vA->visit_concrete_elementA(eA);
    vA->visit_concrete_elementB(eB);
    vB->visit_concrete_elementA(eA);
    vB->visit_concrete_elementB(eB);
    delete vA;delete vB;delete eA;delete eB;
    return 0;
}