ex4 - https://medium.com/@lu4nm3/use-adt-specific-behaviors-on-a-common-interface-76ae82ee27bc

ex4_adt.scala

object Cake {
  implicit val price: Price[Cake] = new Price[Cake] {
    def price(cake: Cake): Double = cake.price
  }
}

object Apple {
  val PricePerLb: Double = 3.0

  implicit val price: Price[Apple] = new Price[Apple] {
    def price(apple: Apple): Double = PricePerLb * apple.weightLbs
  }
}

object Shampoo {
  implicit val price: Price[Shampoo] = new Price[Shampoo] {
    def price(shampoo: Shampoo): Double = shampoo.price
  }
}

// etc