> By ensuring that developers and architects conform to certain conventions
Enforcing conventions is of course a good thing! The problem is how Go enforces conventions:
(0) When Go enforces a convention mechanically, it's a triviality that can be adequately handled by external tools (e.g., naming, formatting, unused variables, etc.).
(1) When a convention is actually useful (e.g., the correct way of using an interface), Go's type system is too dumb to understand it, let alone enforce it.
> aren't performant enough for new features
Second-class parametric polymorphism (“generics”) is purely a compile-time feature. It can be completely eliminated (that is, turned into the non-generic code you would've written otherwise) using a program transformation called “monomorphization”, before any target machine code is generated. So there's no runtime price to be paid.
To be precise, you need to outlaw polymorphic recursion to be able to do full monomorphisation. I'm not sure if that's what you meant by "second-class" in this context
First-class polymorphism is what System F gives you: functions from types to values.
Second-class polymorphism is what Damas-Milner gives you: let-bound identifiers may admit more than one type, in which case every type they admit is subsumed by a type schema.
Second-class polymorphism rules out polymorphic recursion if you consider every recursive definition as syntactic sugar for applying a fixed point combinator to some expression of type `a -> a`, for whatever monotype `a`.
That's a new turn of the phrase for me. I've only ever heard the expression "second-class parametric polymorphism" used in reference to enforcing predicativity (which does not rule out polymorphic recursion)
Enforcing conventions is of course a good thing! The problem is how Go enforces conventions:
(0) When Go enforces a convention mechanically, it's a triviality that can be adequately handled by external tools (e.g., naming, formatting, unused variables, etc.).
(1) When a convention is actually useful (e.g., the correct way of using an interface), Go's type system is too dumb to understand it, let alone enforce it.
> aren't performant enough for new features
Second-class parametric polymorphism (“generics”) is purely a compile-time feature. It can be completely eliminated (that is, turned into the non-generic code you would've written otherwise) using a program transformation called “monomorphization”, before any target machine code is generated. So there's no runtime price to be paid.