Benjamin

factory工厂模式实际上polymorphic factory多态工厂的特例。
#include <iostream>
#include <map>
#include <string>
#include <vector>
#include <stdexcept>
#include <cstddef>
#include "../purge.h"
using namespace std;

class Shape{
public:
   virtual void draw()=0;
   virtual void erase()=0;
   virtual ~Shape();
};

class ShapeFactory{
   virtual Shape* create()=0;//不能直接调用，可以覆盖
   static map<string,ShapeFactory*> factories;
public:
   virtual ~ShapeFactory() {}
   friend BadShapeFactoryInitializer;//map和工厂对象的初始化
   class BasdShapeCreation:public logic_error{
public:
   BagShapeCreation(string type):logic_error("Cannot create type"+type){}
};
static Shape* creatShape(const stirng& id) throw(BadShapeCreation){
   if(factories.find(id) != factories.end())//找工厂对象根据传进来的标识符
      return factories[id]->create();
  else
      throw BadShapeCreation(id);
   }
};//Shape对象的创建处

//define the static object
map<string,ShapeFactory*> ShapeFactory::factories;

class Circle:public Shape{
   Circle();//private constructor
   friend class ShapeFactoryInitializer;
   class Factory;
   friend class Factory;
   class Factory:public ShapeFactory{
public:
   Shape* create(){return new Circle;}
   friend class ShapeFactoryIninitializer;
};
public:
   void draw(){cout << "Circle::draw"<<endl;}
   void erase(){cout << "Circle::erase"<<endl;}
   ~Circle(){cout<<"Circle::~Circle"<<endl;}
};

class Square:public Shape{
   Square();//private constructor
   friend class ShapeFactoryInitializer;
   class Factory;
   friend class Factory;
   class Factory:public ShapeFactory{
public:
   Shape* create(){return new Square;}
   friend class ShapeFactoryIninitializer;
};
public:
   void draw(){cout << "Square::draw"<<endl;}
   void erase(){cout << "Square::erase"<<endl;}
   ~Square(){cout<<"Square::~Square"<<endl;}
};

//Singleton to initialize the ShapeFactory:
class ShapeFactoryInitializer{
   static ShapeFactoryInitializer si;
   ShapeFactoryInitializer(){
   ShapeFactory::factories["Circle"] = new Circle::Factory;
   ShapeFactory::factiories["Square"] = new Square::Factory;
   }
   ~ShpaeFactoryInitializer(){
   map<string,ShapeFactory*>::iterator it= ShapeFactory::factories.begin();
   while(it != ShapeFactory::factories.end())
   delete  it++->second;
   }
};

//static member definition
ShapeFactoryInitializer ShapeFactoryInitializer::si;

char* si[]= {"Circle","Square","Square","Circle","Circle","Circle","Square"};

int main()
{
vector<Shpae*> shapes;
try{
   for(size_t i=0; i <sizeof(si)/sizeof(si[0]); i++)
   {
         shape.push_back(ShapeFactory::createShape(si[i]));
   }catch(ShapeFactory::BadShapeCreation e){
      cout<<e.what()<<endl;
      return EXIT_FAILURE;
   }
   for(size_t i = 0; i <shape.size();i++)
   {
      shapes[i]->draw();
      shapes[i]->earse();
   }
      purge(shapes);
   }
} 
这里如果不需要创建单独的工厂对象，尽可能使用static工厂模式。