用抽象类型交换类型参数 [英] Exchanging type parameters with abstract types

问题描述

为了避免在对参数化类进行子类化时重复类型参数信息，我尝试重写一些代码以使用抽象类型.

To avoid having to repeat type parameter information when subclassing parameterized classes, I'm trying to rewrite some code to use abstract types instead.

我想表达的类似于:

class Group[A]

abstract class Thing[A, G <: Group[A]] {
  val group: G
}

class SomeGroup[A] extends Group[A] { g =>    
  object SomeThing extends Thing[A, SomeGroup[A]] {
    val group = g
  }
}

使用抽象类型，我目前最好的尝试是:

Using abstract types, my best attempt so far is:

class Group {
  type A
}

abstract class Thing { t =>
  type A
  type G <: Group { type A = t.A }
  val group: G
}

class SomeGroup extends Group { g =>
  object SomeThing extends Thing {
    type A = g.A
    type G = SomeGroup { type A = g.A }
    val group = g
  }
}

但是，我在最后一行收到编译器错误，提示值组具有不兼容的类型".

However, I'm getting a compiler error on the last line saying "value group has incompatible type".

如何使用抽象类型编写第一个示例?

推荐答案

你需要给类型检查器/推断器一些帮助:

You need to give the type checker/inferrer a little help:

val group : G = g

让它通过.

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