Scala 类型橡皮擦

Question

case class Thing[T](value: T)
def processThing(thing: Thing[_]) = {
  thing match {
    case Thing(value: Int) => "Thing of int"
    case Thing(value: String) => "Thing of string"
    case _ => "Thing of something else"
  }
}

println(processThing(Thing(1)))
println(processThing(Thing("hello")))

以上输出Thing of int和Thing of string. 我的问题是，如果类型橡皮擦启动，为什么类型信息在运行时仍然可用？

Answer 1

如果您尝试以下操作，则这不是类型擦除开始的时间：

def processThing(thing: Thing[_]) = {
  thing match {
    case _: Thing[Int] => "Thing of int"
    case _: Thing[String] => "Thing of string"
    case _ => "Thing of something else"
  }
}

println(processThing(Thing("hello")))

你会得到Thing of int。由于case Thing(value: Int)您基本上是在进行与类型断言的模式匹配，我认为它会是这样的：

def processThing(thing: Thing[_]) = {
  thing match {
    case Thing(value) if value.isInstanceOf[Int] => "Thing of int"
    case Thing(value) if value.isInstanceOf[String] => "Thing of string"
    case _ => "Thing of something else"
  }
}