Scala自类型和泛型类 [英] Scala self-type and generic class

问题描述

abstract class Bar[M] {
  def print(t: M): Unit = {
    println(s"Bar: ${t.getClass()}")
  }
}

trait Foo[M] {
  this: Bar[M] =>
  def print2(t: M): Unit = {
    println(s"Foo: ${t.getClass()}")
  }
}

object ConcreteBar extends Bar[Int] with Foo[Int] {}
object ConcreteFooBar extends Bar[Int] with Foo[Int] {}

object Test {
  def main(args: Array[String]): Unit = {
    ConcreteBar.print(1)
    ConcreteFooBar.print2(1)
  }

在上面的示例中，有没有一种方法可以使我们不必在自定义的"bar"特征中重复该类型? 因此，我们可以这样声明ConcreteFooBar:

In the example above, is there a way so that we don't have to repeat the type in the self-typed "bar" trait? Therefore we could declare ConcreteFooBar like this:

object ConcreteFooBar extends Bar[Int] with Foo {}

推荐答案

对于Foo，您可以使用抽象类型而不是类型参数，例如:

You can use an abstract type instead of a type parameter for Foo, like this:

abstract class Bar[M] {
  type Base = M
  def print(t: M): Unit = {
    println(s"Bar: ${t.getClass()}")
  }
}

trait Foo {
  type Base
  def print2(t: Base): Unit = {
    println(s"Foo: ${t.getClass()}")
  }
}

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