> These are two models, inheritance and type classes, which are different > answers to the same problem. I can see no good reason to provide both in the > same language..
I see one difference: with concepts the type match is an implicit one, the person creating the matching concrete type doesn't even have to now that the concept exists. With inheritance, it is explicit: the creator of a derived type explicitly mentions the base type in the type definition. This implies that he is aware of the semantics that cannot be checked by a compiler. A concept match checks that, e.g., a certain proc is defined for the matched type. The creator of that proc never promised that this proc will actually do what we think it will.
