Scala模式匹配和类型推断

Question

有人可以解释为什么以下代码编译？

Option("foo") match {
  case x: List[String] => println("A")
  case _ => println("B")
}

这给了我关于类型擦除的(预期)警告,但它仍然编译.我希望这会抛出一个类型错误,就像我匹配"foo"而不是Option("foo").

谢谢!

Answer 1

我假设编译器将 和 视为Option和List，Product这就是它编译的原因。正如您所说，有关类型擦除的警告是预期的。这是使用另一个产品的示例：

scala> Option("foo") match {
 | case x: Tuple2[String,String] => println("TUPLE")
 | case x: List[String] => println("LIST")
 | case _ => println("OTHER")
 | }
<console>:9: warning: non variable type-argument String in type pattern (String, String)       is unchecked since it is eliminated by erasure
          case x: Tuple2[String,String] => println("TUPLE")
                  ^
<console>:10: warning: non variable type-argument String in type pattern List[String] is unchecked since it is eliminated by erasure
          case x: List[String] => println("LIST")
                  ^

更新 w/r/t 案例类（因为下面的评论）：

scala> case class Foo(bar: Int)
defined class Foo

scala> val y: Product = Foo(123)
y: Product = Foo(123)