Decoration with several interface

Question

I am always struggling with decoration + interfaces. Say I have the following \'behavior\' interfaces :

interface IFlyable { void Fly();}
interface ISwimmable {          


        

Answer 1

I think you are steering right into the service locator pattern - which is a severe anti-pattern. You have a service locator, if you depend on an interface that acts like a wishing well: you can ask it for anything. I think that this is exactly where your GetAs is getting you to.

Service locator is considered an anti-pattern because it hides the dependencies that a class has. Instead, you only see the service locator as single dependency but you don't immediately see what dependencies are going to be called.

If you ask for an implementation, I would recommend to use a dependency injection framework. There are plenty of them on the market like MEF, Ninject, Unity, Windsor, DryIoC, SimpleInject, LightInjector, Grace, Stashbox, ... just to name a few that come to my mind.

The point of a decorator is something completely different. A decorator is used if you do NOT just forward the interface calls, but add some extra logic (such as a retry behaviour) to it. In that case, you would however still limit yourself to the methods of the original interface.