How can I make this simple C# generics factory work?
- by Kevin Brassen
I have this design:
public interface IFactory<T> {
T Create();
T CreateWithSensibleDefaults();
}
public class AppleFactory : IFactory<Apple> { ... }
public class BananaFactory : IFactory<Banana> { ... }
// ...
The fictitious Apple and Banana here do not necessarily share any common types (other than object, of course).
I don't want clients to have to depend on specific factories, so instead, you can just ask a FactoryManager for a new type. It has a FactoryForType method:
IFactory<T> FactoryForType<T>();
Now you can invoke the appropriate interface methods with something like FactoryForType<Apple>().Create(). So far, so good.
But there's a problem at the implementation level: how do I store this mapping from types to IFactory<T>s? The naive answer is an IDictionary<Type, IFactory<T>>, but that doesn't work since there's no type covariance on the T (I'm using C# 3.5). Am I just stuck with an IDictionary<Type, object> and doing the casting manually?
