Question

我有以下问题：我希望有一个＆＃39;实例＆＃39; （参数化特征）和＆＃39;配置＆＃39;，后者由实例类型参数化：

trait Kind
trait Kind1 extends Kind
trait Kind2 extends Kind

trait Instance[T <: Kind] {
  def configuration: InstanceConfiguration[Instance[_]]
}

trait InstanceConfiguration[+T <: Instance[_]] {
}

class AInstance extends Instance[Kind1] {
  override def configuration: AConfiguration = ???
}

class AConfiguration extends InstanceConfiguration[AInstance] {
}

class BInstance extends Instance[Kind1] {
  override def configuration: AConfiguration = ???
}

所以，问题是InstanceConfiguration[Instance[Kind2]]不能用作Instance[Kind1]的配置，但现在它太通用了，我想编译器在{{1}上发出错误}}

那么如何更改Instance trait中的配置定义以引用具体类型的具体InstanceConfiguration？

Answer 1

您需要使用F-Bounded多态性。我建议在Twitter的Scala学校阅读the section，但简而言之，Instance需要将具体类型作为类型参数：

trait Kind
trait Kind1 extends Kind
trait Kind2 extends Kind

trait Instance[A <: Instance[A, T], T <: Kind] {
  self: A =>
  def configuration: InstanceConfiguration[A]
}

trait InstanceConfiguration[+T <: Instance[_, _]] {
}

class AInstance extends Instance[AInstance, Kind1] {
  override def configuration: AConfiguration = ???
}

class AConfiguration extends InstanceConfiguration[AInstance] {
}

class BInstance extends Instance[BInstance, Kind1] {
  override def configuration: AConfiguration = ???
}

在参数化特征中引用自我类型

1 个答案: