Comment by zozbot234
6 years ago
> Of course I know I will remove all protocols from that part of the app and lose some of the "beauty"
Protocols/traits/interfaces are just indirection - we all know that indirect calls are expensive. Fixing this need not be a loss in "beauty" if the language design makes direct calls idiomatic enough.
> And now that the linked article also explains the costs of ABI stability
I definitely agree about this, though. ABI stability and especially ABI-resilience, have big pitfalls if used by default, without a proper understanding of where these drawbacks could arise. They are nowhere near "zero cost"!
Rust allows you to opt for static dispatch with traits when possible so that there is no runtime cost. See https://doc.rust-lang.org/1.8.0/book/trait-objects.html
> Protocols/traits/interfaces are just indirection
They are indeed. Look at how C++ handles multiple inheritance, for example: literally a few extra instructions for each method call, not more than that. Swift's cost of protocol method call and typecasting seems too high in comparison, and I haven't even tried this across dylibs yet.
> literally a few extra instructions for each method call, not more than that.
Yup, C++ does this by building in lightweight RTTI info as part of the vtable. Swift expands on this trick by using broadly-similar RTTI info to basically reverse excess monomophization of generic code. (Rust could be made to support very similar things, but this does require some work on fancy typesystem features. E.g. const generics, trait-associated constants, etc.)