设计模式——简单工厂模式（Simple Factory）

• 即将对象创建封装到工厂类中，用户传递参数给工厂对象，获取相应对象。
• 通过多态，将用户与具体对象隔离开

• 

• 代码示例

  #include <iostream>
  #include <string>
  using namespace std;
  
  //product
  class Shape 
  {
  public:
      virtual void draw() = 0;
      virtual ~Shape() {}
  };
  
  class Circle : public Shape 
  {
  public:
      void draw() { cout << "Circle::draw" << endl; }
      ~Circle() { cout << "Circle::~Circle" << endl; }
  private:
      Circle() {}
      friend class SimpleFactory;
  };
  
  class Square : public Shape 
  {
  public:
      void draw() { cout << "Square::draw" << endl; }
      ~Square() { cout << "Square::~Square" << endl; }
  private:
      Square() {}
      friend class SimpleFactory;
  };
  
  //factory
  class SimpleFactory
  {
  public:
      static Shape* create(const string& type)
      {
          if(type == "Circle") return new Circle;
          if(type == "Square") return new Square;
          //...
          return NULL;
      }
  };
  
  int main() 
  {
      Shape* pShape1 = SimpleFactory::create("Circle");
      Shape* pShape2 = SimpleFactory::create("Square");
  
      pShape1->draw();
      pShape2->draw();
  
      delete pShape1;
      delete pShape2;
  
      return 0;
  }