Can I limit generic type argument to be one of 2 unrelated classes?

Question

I'd like to be able to do something like this (won't actually work):

class A[T <: B | C]

... and expect this to be valid:

new A[B]
new A[C]

... and this to yield compiller error:

new A[D]

Is something like this possible?

Answer 1

You could use implicits:

trait AArg[T]

class A[T](implicit e: AArg[T])

implicit val argB = new AArg[B] { }
implicit val argC = new AArg[C] { }

although this doesn't prevent someone from creating an implicit val of type AArg[D].