I don't understand his comment, "I'm disappointed to see that Scala has largely preserved Java's inheritance model." This directly translates to scala:

    trait Priceable {
      def price: Int
    }

    def addToCart(cart: Cart, item: Priceable) {
      cart.increaseTotal(item.price)
    }

    class Book extends Priceable {
       ...same thing...
    }

The only thing non-idiomatic about this in Scala is the use of a mutable cart.