SE-0452: Integer Generic Parameters

[Joe_Groff]

@rauhul

This works with type parameters:

func inferType<T>(_: T.Type = T.self) -> T { fatalError() }

let x = inferType(String.self)
type(of: x) // String.self

This doesn't work with int value parameters

func inferValue<let newCount: Int>(_: Int = newCount) -> Vector<newCount, Int> { fatalError() }

let x = inferValue(10) // error: unable to infer return type

I would really like to see this restriction lifted in this proposal.

That syntax declares the value of newCount as a default argument for the value parameter, so we can't use literally this syntax. This only works for type parameters indirectly, because a metatype T.Type already exists for every type T, and it only has one possible value T.self, so the metatype parameter acts as a way to force T to be a specific type at a call site. It might be nice to revisit the ability to explicitly provide generic arguments instead of coming up with something bespoke.

@rauhul

I found myself needing to refer to Vector.count frequently, e.g.:

struct StrongType {
  typealias Bytes = Vector<13, UInt8>
  var bytes: Bytes
}

// use: StrongType.Bytes.count 

Could you clarify what you mean? If Vector has a static var count member, then StrongType.Bytes.count would already work.