type-projection.scala

trait SuperC[A,B] {
  def getB(a: A): B
  // ...
}

trait Foo {
  type A
  type B
  type C <: SuperC[A,B]
  // ...
}

class Bar[F<:Foo](a: F#A, c: F#C) {
  val b = c.getB(a)
}

/*
error: type mismatch;
 found   : Bar.this.a.type (with underlying type F#A)
 required: _81.A where val _81: F
         val b = c.getB(a)
                        ^
*/

class MyFoo extends Foo {
  type A = Int
  type B = Int
  type C = MyC
  // ...
}
trait MyC extends SuperC[Int,Int] {
  // ...
}
class MySubC extends MyC{
  def getB(a: Int): Int = ???
  // ...
}