final case class Failure[+T](exception: Throwable) extends Try[T]`

final case class Failure(exception: Throwable) extends Try[Nothing]`

object None extends Option[Nothing]

def zip[U](that: Future[U]): Future[(T, U)] = {
  implicit val ec = internalExecutor
  val p = Promise[(T, U)]()
  onComplete {
    case f: Failure[_] => p complete f.asInstanceOf[Failure[(T, U)]]
    case Success(s) => that onComplete { c => p.complete(c map { s2 => (s, s2) }) }
  }
  p.future
}

case f: Failure[_] => p complete f.asInstanceOf[Failure[(T, U)]]

case f: Failure => p complete f