Is there a shorthand for type variable 'm forSome { type m[O] <: UpperBound[O] }` in Scala?

Question

Problem:

trait UpperBound[O]
trait High[F[O] <: UpperBound[O]]

def canEqual(that :Any) = that.isInstanceOf[High[_]]

def high(h :High[_]) = ???

Answer 1

• If you make existential quantization outside High then it's just

  type T = High[F] forSome { type F[O] <: UpperBound[O] }
  
  def canEqual(that: Any) = that.isInstanceOf[T]
  
  def high(h: T) = ???
  

• If you make existential quantization inside High then since

  implicitly[(n forSome { type n <: Upper}) =:= Upper]
  implicitly[(m[O1] forSome { type m[O] <: UpperBound[O]}) =:= UpperBound[O1]]
  

  (and vice versa) it's just High[UpperBound]

  implicitly[High[m forSome { type m[O] <: UpperBound[O] }] =:= High[UpperBound]]
  
  def canEqual(that: Any) = that.isInstanceOf[High[UpperBound]]
  
  def high(h: High[UpperBound]) = ???
  

  An existential type