lu4nm3

val ints = new Set() // assuming Set was implemented
ints.add(1.0)
ints.add(3.0)

scala> ints.get(0)
res0: Any = 1.0

scala> ints.get(0).asInstanceOf[Double]
res1: Double = 1.0

lu4nm3

trait DoubleSet {
  def get(index: Long): Double
  def add(value: Double): Set
}

trait StringSet {
  def get(index: Long): String
  def add(value: String): Set
}

lu4nm3

trait Set[A] {
  def get(index: Long): A
  def add(value: A): Set[A]
}

lu4nm3

val doubles = new Set[Double]()
doubles.add(1.0)
doubles.add(3.0)

scala> doubles.get(0)
res1: Double = 1.0

val strings = new Set[String]()
strings.add("one")
strings.add("two")

lu4nm3

trait Perishable {
  def expired: Boolean
}

case class Baguette() extends Perishable {
  def expired: Boolean = ???
}

case class Croissant() extends Perishable {
  def expired: Boolean = ???

lu4nm3

trait DailyOrderService {
  def needsReplacing(perishables: List[Perishable]): List[Perishable] = {
    perishables.filter(_.expired)
  }
}

lu4nm3

trait PerishableLike[A] {
  def expired: Boolean
}

case class PerishableLikeBaguette(b: Baguette) extends PerishableLike[Baguette] {
  def expired: Boolean = ???
}

case class PerishableLikeCroissant(c: Croissant) extends PerishableLike[Croissant] {
  def expired: Boolean = ???

lu4nm3

def needsReplacing[T](perishables: List[PerishableLike[T]]): List[PerishableLike[T]] = {
  perishables.filter(_.expired)
}

lu4nm3

trait Perishable[T] {
  def expired(item: T): Boolean
}

lu4nm3

case class Baguette()
case class Croissant()