Factory Pattern but with object Parameters

Question

Take the following classic factory pattern:

public interface IPizza
{
    decimal Price { get; }
}

public class HamAndMushroomPizza : IPizza
{
    decimal IPizza.Price
    {
        get
        {
            return 8.5m;
        }
    }
}
public abstract class PizzaFactory
{
    public abstract IPizza CreatePizza(ItalianPizzaFactory.PizzaType pizzaType);
}

public class ItalianPizzaFactory : PizzaFactory
{
    public enum PizzaType
    {
        HamMushroom,
        Deluxe,
        Hawaiian
    }

    public override IPizza CreatePizza(PizzaType pizzaType)
    {
        switch (pizzaType)
        {
            case PizzaType.HamMushroom:
                return new HamAndMushroomPizza();
            case PizzaType.Hawaiian:
                return new HawaiianPizza();
            default:
                throw new ArgumentException("The pizza type " + pizzaType + " is not recognized.");
        }
    }
}

What if one (or many) of the Concrete Pizzas requires a parameter specific to the concrete implementation at construction. For example, lets say the HamAndMushroom factory requires a parameter called, MushroomType and this parameter would be required to instantiate the object?

Answer 1

You can add parameters to the creator method(s) of your factory. However, if the number of parameters is getting higher (for me that would be more than 2-3), and especially if some or all of those parameters are optional with reasonable default values, you may consider turning the factory into a Builder instead.

That may be especially appropriate for pizzas, where you usually have the same crust, just with different (combinations) of toppings. A Builder models very closely the common way of ordering e.g. "a pizza with salami, tomatoes, maize and double cheese". OTOH for "predefined" pizzas you may want to define helper factory methods, e.g. createMargaritaPizza or createHawaiiPizza which then internally use the builder to create a pizza with the toppings specific to that kind of pizza.