scala - 如何避免 'Non-variable type argument is unchecked since it is eliminated by erasure' ？

Question

我正在处理的一个项目有以下代码:

val ftr1: Future[Try[(Date, String)]] = Future {
  if (someCondition) {
    // some code
    val amazonClient = Try[new com.amazonaws.services.s3.AmazonS3Client(...)]
    amazonClient.map { c => 
    // doing some stuff
    (new Date, "SomeString")
    }
  } else {
    // some code
    Failure(new Exception)
  }
}

Future.firstCompletedOf(Seq(ftr1, anotherFuture)) map {
  case t: Try[(Date, String)] => {
    t match {
      case Success(r) => //do some things
      case _ => //do some another things
  }
  case _ => //do some another things
}

因此，在编译期间，我有以下警告:

[warn] non-variable type argument java.util.Date in type pattern java.util.Date, String) is unchecked since it is eliminated by erasure

和

[warn] case t: (Date, String) => //do some things

我实际上不明白，这些警告是什么意思，如何重构这段代码以摆脱这些警告？

Answer 1

Try[+T]是一个抽象类，您不能为其创建实例。

有两个案例类继承自它，Success和 Failure ，您应该真正使用它。

编译器警告您，在编译时，类型删除将删除这些类型，因此对它们进行匹配不会得到您想要的结果。有关更多信息，请访问 How do I get around type erasure on Scala? Or, why can't I get the type parameter of my collections?

但是，如果您只需匹配 Success 就可以完全避免这一切。和 Failure减少比赛中不必要的嵌套:

val ftr1: Future[Try[(Date, String)]] = Future {
  if (someCondition) {
    // some code
    val amazonClient = Try { /* stuff */ }
    amazonClient.map { c => 
    // doing some stuff
    (new Date, "SomeString")
  } else Failure(new Exception)
}

Future.firstCompletedOf(Seq(ftr1, anotherFuture)) map {
   case Success((date, myString)) => /* do stuff */
   case Failure(e) => log(e)
}