scala> isWeakSubType(typeOf[Int], typeOf[Double])
res0: Boolean = true

scala> isWeakSubType(typeOf[Int].narrow, typeOf[Double])
res1: Boolean = false

object AdaptWithWeaklyConformantType {
  implicit class D(d: Double) { def double = d*2 }

  val x1: Int = 1
  var x2: Int = 2
  val x3 = 3
  var x4 = 4
  final val x5 = 5
  final var x6 = 6

  def f1 = x1.double
  def f2 = x2.double
  def f3 = x3.double
  def f4 = x4.double
  def f5 = x5.double
  def f6 = x6.double
}