|
|
|
|
|
|
by angersock
4383 days ago
|
|
|
So, this may simply be a massive gap in my understanding of theory and PL stuff. :) My reasoning is that an inheritance-based language has some notion of "A extends B extends C", and so if I need to check compatibility of types I can just walk the class hierarchy and get an answer. I'm clearly missing something--maybe I'm just using the wrong mental model for types? |
|
|
For languages with parametric polymorphism, note that inheritance is kind of like subtyping. Getting subtyping correct in the presence of parametric polymorphism is famously subtle; see http://en.wikipedia.org/wiki/Covariance_and_contravariance_(...
For languages without parametric polymorphism, it's easy to see why inheritance makes things more complicated. In the case of nominal typing, this walking you describe isn't necessary without inheritance -- a value either is or is not in the exact named type it's supposed to be. In the case of structural typing, it suffices to say that inheritance complicates type inference.
Inheritance is actually even more subtle than subtyping even; e.g. consider http://en.wikipedia.org/wiki/Fragile_base_class