Factory class

[KeepYourMind]

Hello. I'm try to write factory class but have some problems.
Source example:

// Pizza interface
interface IPizza
{
    void doSome();
}

// Pizza
class IMPizza : IPizza
{
    void doSome() {}
}

// try to raise functinally
class CoolPizza : IPizza
{
    void doSome() {}
    void doSomeA() {}
}

// Factory
static class PizzaFactory
{
    static IPizza factory(char[] name)
    {
        switch (name) {
            case "im":
                return new IMPizza;
                break;
            case "cool":
                return new CoolPizza;
                break;
            default:
                throw new Exception("incorrect pizza name");
                break;
        }
    }
}

// run
void main()
{
    auto pizza = PizzaFactory.factory();
    pizza.doSome(); // OK
    pizza.doSomeA(); // error: IPizza.doSomeA() not found
}

What i need to do for pizza.doSomeA() begin work?