scala - Scala中的联合类型子类型

Question

我可以使用 Dotty 轻松完成以下操作：

trait Ex {type T <: Int | Seq[Int]; def f:T}

trait Ex2 extends Ex {override type T = Seq[Int]; override def f = Seq(2)}

trait Ex3 extends Ex {override type T = Int; override def f = 2}

如何在没有 Dotty 的情况下进行联合类型子类型化？

Answer 1

简单的解决方案是上限类型：

trait Ex {type T >: Int with Seq[Int]; def f:T}

trait Ex2 extends Ex {override type T = Seq[Int]; override def f = Seq(2)}

trait Ex3 extends Ex {override type T = Int; override def f = 2}