相关疑难解决方法(0)

scala.util.Failure 声明如下:

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

它需要一个T看起来完全不必要的类型参数,给出如何Failure轻松地声明为子类型Try[Nothing]:

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

以与None声明相同的方式:

object None extends Option[Nothing]

实际上,额外的类型参数在其他地方成为痛点.这是Future.zip:

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
} …