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by angersock 4383 days ago
Some great points!

Out of curiosity, does anyone know of any studies/inquiries into the interaction of type systems with languages that favor composition over inheritance? I imagine that a more inheritance-driven language would be more amenable to strong type checking, for example.
1 comments
nmrm 4383 days ago
angersock,

> I imagine that a more inheritance-driven language would be more amenable to strong type checking, for example.

AFAIK the conventional wisdom among formal methods people is actually the opposite.

If you don't mind my asking, why do you imagine this?

> does anyone know of any studies/inquiries into the interaction of type systems with languages that favor composition over inheritance?

I'm not sure what you mean. Do you mean studies about interactions between type systems of these two sorts (e.g. as in Scala)? Or do you mean a comparative study asking which is better?

As I mentioned, I think the conventional wisdom is that inheritance makes things more difficult from a type checking/verification perspective. For this reason, the big arguments for inheritance tend to be oriented toward pragmatism rather than ease of formal reasoning.

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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?

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nmrm 4383 days ago
> so if I need to check compatibility of types I can just walk the class hierarchy and get an answer.

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

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