Given:
sealed trait F
sealed trait K extends F
case object K1 extends K
sealed trait L extends F
case object L1 extends L
Using the above hierarchy, how can I define a function that, at compile-time, has a List of type A that is either all K's or L's, i.e. the super-type must be either K or L, but not F?
Example:
f(List(K1, K1)) would compile since the list's super-type is K
but
f(List(K1, L1)) would not since the list's super-type is F
You can start with Miles Sabin's answer at Enforce type difference and adapt:
implicit def notSubtype[A, B]: >!>[A, B] = null
implicit def ambig1[A, B >: A]: >!>[B, A] = null
implicit def ambig2[A, B >: A]: >!>[B, A] = null
def f[A >: K with L](xs: List[A])(implicit ev: A >!> F) = xs
f(List(K1, K1)) // compiles
f(List(K1, L1))
[error] /tmp/rendererB0Um6L4t45/src/main/scala/test.scala:23: ambiguous implicit values:
[error] both method ambig1 in object Main of type [A, B >: A]=> >!>[B,A]
[error] and method ambig2 in object Main of type [A, B >: A]=> >!>[B,A]
[error] match expected type >!>[F,F]
[error] f(List(K1, L1))
[error] ^
Either, though I've never liked its syntax much