ex7 - https://medium.com/@lu4nm3/use-adt-specific-behaviors-on-a-common-interface-76ae82ee27bc

ex7_adt.scala

object Item {
  implicit val price: Price[Item] = new Price[Item] {
    def price(item: Item): Double = item match {
      case cake: Cake => Cake.price.price(cake)
      case baguette: Baguette => Baguette.price.price(baguette)
      case apple: Apple => Apple.price.price(apple)
      case orange: Orange => Orange.price.price(orange)
      case shampoo: Shampoo => Shampoo.price.price(shampoo)
      case toothPaste: ToothPaste => ToothPaste.price.price(toothPaste)
    }
  }
}

object Fruit {
  implicit val price: Price[Fruit] = new Price[Fruit] {
    def price(fruit: Fruit): Double = fruit match {
      case apple: Apple => Apple.price.price(apple)
      case orange: Orange => Orange.price.price(orange)
    }
  }
}

...