public class Creator
public static IVehicle Create(VehicleType vehicleType)
IVehicle vehicle = new Chisasa();
vehicle = new Sedan();
vehicle = new FourByFour();
This decision structure is easily refactored to an in-memory type registry which uses the lookup metaphor as demonstrated below:
private IDictionary<VehicleType,IVehicle> Vehicles
IDictionary<VehicleType,IVehicle> vehicles = new Dictionary<VehicleType,IVehicle>();
vehicles.Add(Vehicle.Sedan, new Sedan());
vehicles.Add(Vehicle.Mazembe, new Mazembe());
vehicles.Add(Vehicle.Chisasa, new Chisasa());
vehicles.Add(Vehicle.Chimbayambaya, new Chimbayambaya());
public static IVehicle Find(VehicleType vehicleType)
If you are observant, you will notice that this changes the semantics of the implementation. We have now moved from creating objects to finding objects in a registry. Sound familiar? This emergent design shows us that the Factory Method is really a respository pattern in disguise. Refactoring a GOF pattern has teleported us to one of the basic tenets of Domain Driven Design, the Repository Pattern.
Some considerations to take into account would be deciding the best collection to use
to reduce the cost of lookup. It could also be possible to externalise the registry depending on the nature of the problem space.