My Opt type implementation

opt_type.scala

sealed trait Opt[+A] {
  def flatMap[T](f: A => Opt[T]): Opt[T] = 
    fold[Opt[T]](Nothing)(f)
 
  def map[T](f: A => T): Opt[T] = 
    fold[Opt[T]](Nothing)(a => Something(f(a)))
 
  def fold[B](g: => B)(f: A => B): B =
    this match {
      case Something(a) => f(a)
      case Nothing => g
    }
}
 
case class Something[A](value: A) extends Opt[A]
case object Zero extends Opt[Nothing]