Abstract Factory

Description:

Creates an instance of several families of classes

Intent

• Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
• A hierarchy that encapsulates: many possible "platforms", and the construction of a suite of "products".
• The new operator considered harmful.

Example:

Note

Idea:

感觉和factory method的区别就是这个有多个不同的factory。

Check list

1. Decide if "platform independence" and creation services are the current source of pain.
2. Map out a matrix of "platforms" versus "products".
3. Define a factory interface that consists of a factory method per product.
4. Define a factory derived class for each platform that encapsulates all references to the new operator.
5. The client should retire all references to new, and use the factory methods to create the product objects.

Code:

#include <iostream>
#include <vector>
#include <cmath>
#define LINUX

using namespace std;

class Widget{
public:
    virtual void draw() = 0;    
    virtual ~Widget() {} // virtual destructor will call derived class destructor
};

class LinuxButton: public Widget{
public:
    void draw() override { cout<<"LinuxButton\n"; }
};
class LinuxMenu: public Widget{
public:
    void draw() override { cout<<"LinuxMenu\n"; }
};

class WindowsButton : public Widget {
 public:
  void draw() { cout << "WindowsButton\n"; }
};
class WindowsMenu : public Widget {
 public:
  void draw() { cout << "WindowsMenu\n"; }
};

class Factory{
public:
    virtual Widget * createButton() = 0;
    virtual Widget * createMenu() = 0;
};

class LinuxFactory : public Factory{
public:
    Widget * createButton(){
        return new LinuxButton;
    }
    Widget * createMenu(){
        return new LinuxMenu;
    }
};

class WindowsFactory : public Factory{
public:
    Widget * createButton(){
        return new WindowsButton;
    }
    Widget * createMenu(){
        return new WindowsMenu;
    }
};

class Client{
private:
    Factory * factory;
public:
    Client(Factory *f): factory(f) {}

    void draw(){
        Widget *w_b = factory->createButton();
        Widget *w_m = factory->createMenu();
        w_b->draw();
        w_m->draw();
    }
};


int main(){
    Factory * factory;

#ifdef LINUX
    factory = new LinuxFactory;
#else
    factory = new WindowsFactory;
#endif

    Client *c = new Client(factory);
    c->draw();
}