Factory design pattern
 

I have this class:

class Pizza{

protected:

 string desc;

public: 

 Pizza(){

  desc = "unknown pizza";

 }

 virtual string getdesc(){

  return desc;

 }

 virtual double cost(){

  return 0;

 }

};

And one of its subclass:

class Small: public Pizza{

public:

 Small(){

  desc = "Small";

 }

 double cost(){

  return 8.00;

 }

};

Besides the "Small" class there are others that are similar, eg. "Medium", "Large", etc.

I want to implement a Factory class for this. However, it doesnt seem to work:

class PizzaFactory: public Pizza{

public:

 Pizza* getPizzaInstance( int id );

};

 

Pizza* PizzaFactory::getPizzaInstance( int id ) {

 switch (id) {

 case 1:

  return new Small();

 case 2:

  return new Medium();

  default:

  return NULL;

 }

}

I wonder why when i called in main, it does not give me error but the "id" parameter does not get included into the switch statement.

Any help would be much appreciated.

Re: Factory design pattern
 

There is nothing wrong with your code except "class PizzaFactory: public Pizza{". You don't need to derive factory class from base class. Although this would not cause any fatal problems.
Post your main and the some more description of the problem.

Re: Factory design pattern
 

The reason i derive factory class from base class is because i want to call the member function of class Pizza directly.

The idea of this is simple. I have class Pizza, its derived classes such as Small, Medium, Large. Now that i want to have a Factory class so that by calling this Factory Class a certain derived class (Small, for instance) will be created, instead of creating new instance by calling directly Small.

Main is as follow:

int main(){

 

 PizzaFactory *p2 = new PizzaFactory;

 p2->getPizzaInstance(1);

 

 cout<<p2->getdesc()<<" $"<<p2->cost()<<endl;

 return 0;

}

It does not give any error but the pizza created is a pizza of type Pizza (generic) and not that of Small, which should have been the one since i call getPizzaINstance(1).

What am i missing?

Thanks

Re: Factory design pattern
 

I think i got this one. I'll see if anything else coming up.

Re: Factory design pattern
 

So the problem is with main() and not those classes.. Again you shouldn't derive factory from the base.. it's against the pattern..
Change the main() to:

int main(){

    PizzaFactory *p2 = new PizzaFactory;

    Pizza* p = p2->getPizzaInstance(1);



    cout<<p->getdesc()<<" $"<<p->cost()<<endl;

    return 0;

}