Explict kind declarations on types

[brson]

It's happened to me several times that I've known that a type needed to be Send or Const, but I didn't find out until after I had already defined it and tried to use it with a Send or Const type parameter that it wasn`t the right kind.

Something like this would maybe help:

struct Foo { ... }

impl Foo: Const;

It would basically not do anything except generate an error if it doesn't type check. I might actually prefer that even the kind traits must be declared explicitly.

[bblum]

that rule would make it the same as haskell's "deriving", no? My gut says it's nicer to have it automatically derive and have these as optional -- haskell gets by, but I think it's more often in rust that we rely on satisfying the inherent kinds.

[brson]

Yes, it would be deriving, which is something we are adding for other purposes anyway.

[metajack]

These traits are automatically inferred by the compiler now.