CovarFail.scala

/**
  Here's an example of failing to return the correct type
  */

object CovarianceExampleFailFirst {

  /**
    Covariance example (does not compile)

    def mixFoods[T >: Watermelon](food: T): List[T] = {

    This method definition states that within the context of
    the mixFoodsFail method, there is a type T that is either
    a Watermelon or a subclass of Watermelon.

    Given what we know about type T, this method will accept an argument
    of type T and return a list of type T.

    Unfortuanately, this code will not compile since we are
    attempting to return a GardenItem within the list of what
    can only contain type T.

    */
  def mixFoods[T >: Watermelon](food: T): List[T] = {
    food match {
      case x: FruitSalad => {
        /**
          This will not compile because GardenItem is not a
          subclass of Watermelon; it's a superclass of Watermelon.
          */
        List(new GardenItem, food) // Fails!
      }
      case _ => List()
    }
  }
}