Visitor mode of design mode

Introduce

Visitor—— Abstract Visitor
Abstract class or interface , Declare which elements visitors can access , To be specific to the procedure is visit The parameters of the method define which objects can be accessed .
ConcreteVisitor—— Specific visitors
It affects what visitors do when they visit a class , What are you going to do .
Element—— Abstract elements
Interface or abstract class , State what kind of visitors are allowed to visit , The procedure is through accept Method .
ConcreteElement—— Specific elements
Realization accept Method , Usually visitor.visit(this), Basically, a pattern has been formed .
ObjectStruture—— The structure of the object
The element producer , Generally, it can be accommodated in many different types 、 Containers with different interfaces , Such as List、 Set、 Map etc. , In the project , This character is rarely abstracted

advantage ： Comply with the single responsibility principle ; Excellent scalability ; Very flexible

shortcoming ： Specific elements to visitors to publish details ; It’s difficult to change specific elements ; It violates the principle of inversion of dependence

application ：

An object structure contains many class objects , They have different interfaces , And you want to do something with these objects that depends on their specific classes , In other words, it’s a situation that can’t be competent with iterator mode
Many different and unrelated operations need to be performed on the objects in an object structure , And you want to avoid having these operations “ Pollution ” Classes for these objects

UML Class diagram ：

Simple code ：

#ifndef SIMPLE_VISITOR_H
#define SIMPLE_VISITOR_H
#include <iostream>
#include <typeinfo>
#include <list>
using namespace std;
class Visitor;
class Element
{
public:
virtual void accept(Visitor *visitor) = 0;
};
class ConcreteElementA;
class ConcreteElementB;
/**
* @brief The Visitor class
* Visitor class , In the object structure ConcreteElement Each class of declares a Visit operation .
*/
class Visitor
{
public:
virtual void visitConcreteElementA(ConcreteElementA *ceA) = 0;
virtual void visitConcreteElementB(ConcreteElementB *ceB) = 0;
};
/**
* @brief The ConcreteVisitor1 class
* ConcreteVisitor1, Specific visitors , Implemented by each Visitor Declared operation . Each operation is
* A of the present algorithm . part , The algorithm fragment is the class corresponding to the object in the structure .
*/
class ConcreteVisitor1: public Visitor
{
public:
void visitConcreteElementA(ConcreteElementA *ceA) override
{
cout<<"["<<typeid(ceA).name()<<"] By ["<<typeid (this).name()<<"] visit "<<endl;
}
void visitConcreteElementB(ConcreteElementB *ceB) override
{
cout<<"["<<typeid(ceB).name()<<"] By ["<<typeid (this).name()<<"] visit "<<endl;
}
};
/**
* @brief The ConcreteVisitor1 class
* ConcreteVisitor2, Specific visitors , Implemented by each Visitor Declared operation . Each operation is
* Now part of the algorithm , The algorithm fragment is the class corresponding to the object in the structure .
*/
class ConcreteVisitor2: public Visitor
{
public:
void visitConcreteElementA(ConcreteElementA *ceA) override
{
cout<<"["<<typeid(ceA).name()<<"] By ["<<typeid (this).name()<<"] visit "<<endl;
}
void visitConcreteElementB(ConcreteElementB *ceB) override
{
cout<<"["<<typeid(ceB).name()<<"] By ["<<typeid (this).name()<<"] visit "<<endl;
}
};
class ConcreteElementA : public Element
{
public:
void accept(Visitor *visitor) override
{
visitor->visitConcreteElementA(this);
}
void operationA()
{
cout<<"operationA"<<endl;
}
};
class ConcreteElementB: public Element
{
public:
void accept(Visitor *visitor) override
{
visitor->visitConcreteElementB(this);
}
void operationB()
{
cout<<"operationB"<<endl;
}
};
class ObjectStructure
{
public:
ObjectStructure()
{
m_list.clear();
}
void attach(Element *ele)
{
m_list.push_back(ele);
}
void detach(Element *ele)
{
m_list.remove(ele);
}
void accept(Visitor *vis)
{
for (list<Element*>::iterator it=m_list.begin() ; it != m_list.end(); it++) {
(*it)->accept(vis);
}
}
private:
list<Element*> m_list;
};
#endif // SIMPLE_VISITOR_H


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Big talk design pattern No 28 Chapter , Examples of men and women

UML chart ：

Code ：

#ifndef MAN_WOMEN_VISITOR_H
#define MAN_WOMEN_VISITOR_H
#include <iostream>
#include <typeinfo>
#include <list>
using namespace std;
class Action;
class Men;
class Women;
class Person
{
public:
virtual void accept(Action *act) = 0;
};
class Action
{
public:
virtual void getMenConclusion(Men *men) = 0;
virtual void getWomenConclusion(Women *women) = 0;
};
class Men : public Person
{
public:
void accept(Action *act) override
{
act->getMenConclusion(this);
}
};
class Women : public Person
{
public:
void accept(Action *act) override
{
act->getWomenConclusion(this);
}
};
class Success : public Action
{
public:
void getMenConclusion(Men *men) override
{
cout<<" [ "<<typeid(men).name()<<"] ["<<typeid(this).name()<<" ] when , There's probably a great woman behind her "<<endl;
}
void getWomenConclusion(Women *women) override
{
cout<<" [ "<<typeid(women).name()<<"] ["<<typeid(this).name()<<" ] when , There's an unsuccessful man behind most of them "<<endl;
}
};
class Failing : public Action
{
public:
void getMenConclusion(Men *men) override
{
cout<<" [ "<<typeid(men).name()<<"] ["<<typeid(this).name()<<" ] when , Drinking in a sullen mood , No one needs to persuade ."<<endl;
}
void getWomenConclusion(Women *women) override
{
cout<<" [ "<<typeid(women).name()<<"] ["<<typeid(this).name()<<" ] when , eyes brimming with tears , No one can persuade ."<<endl;
}
};
class Amativeness : public Action
{
public:
void getMenConclusion(Men *men) override
{
cout<<" [ "<<typeid(men).name()<<"] ["<<typeid(this).name()<<" ] when , Pretend to understand everything you don't understand ."<<endl;
}
void getWomenConclusion(Women *women) override
{
cout<<" [ "<<typeid(women).name()<<"] ["<<typeid(this).name()<<" ] when , If you know something, pretend you don't know ."<<endl;
}
};
class ObjectMenWomen
{
public:
ObjectMenWomen()
{
m_list.clear();
}
void attach(Person *ele)
{
m_list.push_back(ele);
}
void detach(Person *ele)
{
m_list.remove(ele);
}
void display(Action *vis)
{
for (list<Person*>::iterator it=m_list.begin() ; it != m_list.end(); it++) {
(*it)->accept(vis);
}
}
private:
list<Person*> m_list;
};
#endif // MAN_WOMEN_VISITOR_H


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5G编程聚合网

由King Wang

Introduce

UML Class diagram ：

Big talk design pattern No 28 Chapter , Examples of men and women

UML chart ：

King Wang

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