type-bounds.scala

class A
class B extends A
class C extends B

class Foo[X] { 
  def x[T >: X] = 1
  def y[T <: X] = 2 
}

val foo = new Foo[B]

foo.x[A] // => OK
foo.x[B] // => OK
foo.x[C]
// <console>:13: error: type arguments [C] do not conform to method x's type parameter bounds [T >: B]
//               foo.x[C]
//                   ^


foo.y[A]
// <console>:12: error: type arguments [A] do not conform to method y's type parameter bounds [T <: B]
//               foo.y[A]
//                   ^

foo.y[B] // => OK
foo.y[C] // => OK