scala - "String with Int"是什么意思？

Question

> val foo: PartialFunction[String, Unit] = { case i: String => }
foo: PartialFunction[String,Unit] = <function1>

> val bar: PartialFunction[Int, Unit] = { case i: Int => }
bar: PartialFunction[Int,Unit] = <function1>

> foo orElse bar
PartialFunction[String with Int,Unit] = <function1>

什么是String with Int? .我认为这甚至不可能。

> (foo orElse bar)(new String with Int)
error: illegal inheritance from final class String
  (foo orElse bar)(new String with Int)
                       ^
error: class Int needs to be a trait to be mixed in
  (foo orElse bar)(new String with Int)
                                   ^

不应该是PartialFunction[Nothing,Unit] ?

Answer 1

What is String with Int?

它是一种交叉类型。 IE。这种类型的值必须是 Int和一个 String同时。

I don't think that's even possible.

是的，这是一种无人居住的类型。但是，一般情况下，如果替换 Int和 String某些类型 A和 B , 你会得到 PartialFunction[A with B, Unit]并且编译器对此没有特殊情况。