Not sure if I interpreted the problem correctly, but in C# composing interfaces and using generic extension methods with type predicates: interface IFooAble {

Not sure if I interpreted the problem correctly, but in C# composing interfaces and using generic extension methods with type predicates: interface IFooAble { ... } interface IBarAble : IFooAble { ... } static class FooProcessor { static T ProcessFoo<T>(T fooInst) where T: IFooAble { ... } } This gives us something that as long as the object implements IFooAble, we can use this extension for free. I.E: IBarAble can use ProcessFoo just fine. This works really well for writing fluent interfaces as demoed above.