Scala isInstanceOf 和类型擦除 [英] Scala isInstanceOf and type erasure

问题描述

我对 isInstanceOf 在 Scala 中的工作方式感到困惑.如果我这样做:

I'm confused as how isInstanceOf works in Scala. If I do something like this:

val x: Int = 5
x.isInstanceOf[Int]

鉴于 Scala 会进行类型擦除，JVM 不应该在运行时删除所有类型信息吗?

Given that Scala does type erasure, shouldn't the JVM remove all type information during runtime?

推荐答案

这不是所有类型信息，只是关于泛型类型的信息.考虑一下:

It's not all type information, just information about generic types. Consider this:

scala> val l = List("foo")
l: List[String] = List(foo)

scala> l.isInstanceOf[List[String]]
res0: Boolean = true

scala> l.isInstanceOf[List[Int]]
<console>:9: warning: fruitless type test: a value of type List[String] cannot also be a List[Int] (the underlying of List[Int]) (but still might match its erasure)
              l.isInstanceOf[List[Int]]
                            ^
res1: Boolean = true

它们都返回true，因为擦除的类型是List.

They both return true, because the erased type is List.

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