Question

下面的代码正在使用ZIO，所以我添加了scalaz标签，尽管这可能与重点无关。我有一个函数，类型为J，带有类型类约束（Job）：

  def execJvm2[J: Job](cmdIn: J): IO[Nothing, Future[RunResult]] = {
    type IOJob = IO[Nothing, J]
    val cmd0: IOJob = omitted(cmdIn)
    val cmd1: IOJob = cmd0.map {
      case cmd : OneShot =>
        memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
        cmd.asInstanceOf[J]
      case cmd: Repl =>
        memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
        cmd.asInstanceOf[J]
      case cmd: ExecFile =>
        memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
        cmd.asInstanceOf[J]
      case _ => ???
    }
    cmd1.map { cmd => poll(cmd.id) }
  }

模式匹配（OneShot，Repl，ExecFile）中的示例都是Job的实例，并且它们的隐式类型类实例在范围内，尽管我猜想有点离题。我认为，在不使用asInstanceOf的情况下应该可以工作的主要原因是，该类型仅在模式匹配中从J缩小为例如OneShot，但我认为编译器也会知道它仍然是J。

Answer 1

看起来有点糟，但我认为

val cmd1: IOJob = cmd0.map { cmdJ => cmdJ match {
  case cmd: OneShot =>
    memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
    cmdJ
  case cmd: Repl =>
    memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
    cmdJ
  case cmd: ExecFile =>
    memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
    cmdJ
  case _ => ???
}}

应该工作。加上类型擦除作弊，我认为这应该可以编译并起作用（但可以尝试）：

val cmd1: IOJob = cmd0.map {
  case cmd: OneShot with J @unchecked =>
    memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
    cmd
  case cmd: Repl with J @unchecked =>
    memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
    cmd
  case cmd: ExecFile with J @unchecked =>
    memStorage(cmd.id) = JobWithResult(cmd, runIO(runInSystem(cmd)))
    cmd
  case _ => ???
}

如何在不使用asInstanceOf的情况下保留匹配中的原始类型？

1 个答案: