Scala 如何具体设置抽象类型与类型绑定？

我试图使用case对象的类型作为抽象类型。我惊讶地看到下面编译的（类似）代码：

sealed abstract class Bar

case object BarOne extends Bar

case object BarTwo extends Bar

sealed abstract class Foo {
  type A <: Bar

  def f: A
}

object Foo {
  object FooOne extends Foo {
    type A = BarOne.type
    val f = BarTwo
  }

  object FooTwo extends Foo {
    type A = BarTwo.type
    val f = BarOne
  }
}

密封抽象类栏
case对象BarOne扩展条
案例对象BarTwo扩展条
密封抽象类Foo{
键入A我不知道这里发生了什么，但我确实将问题隔离了一点。此外，它可以与Foo子类以及对象一起工作。我已确认这在scalac 2.11.8上编译：

object BarOne
object BarTwo

abstract class Foo[A] {
  def attributeType: A
}

object FooContainer {
  class FooOne extends Foo[BarOne.type] {
    val attributeType = BarTwo
  }

  object FooTwo extends Foo[BarOne.type] {
    val attributeType = BarOne
  }
}

A在f:A中被解释为A有人建议您升级到现代版本的Scala吗？（笑话）

关于重写的错误为类型提供了一个很好的路径

$ scala
Welcome to Scala 2.12.0-M5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_92).
Type in expressions for evaluation. Or try :help.

scala> :pa
// Entering paste mode (ctrl-D to finish)

sealed abstract class Bar

case object BarOne extends Bar

case object BarTwo extends Bar

sealed abstract class Foo {
  type A <: Bar

  def f: A
}

object Foo {
  object FooOne extends Foo {
    type A = BarOne.type
    val f = BarTwo
  }

  object FooTwo extends Foo {
    type A = BarTwo.type
    val f = BarOne
  }
}

// Exiting paste mode, now interpreting.

<console>:26: error: overriding method f in class Foo of type => Foo.FooOne.A;
 value f has incompatible type
           val f = BarTwo
               ^
<console>:31: error: overriding method f in class Foo of type => Foo.FooTwo.A;
 value f has incompatible type
           val f = BarOne
               ^

在
FooOne
和
FooTwo
上缺少的
extensed Foo
是一个输入错误吗？因为如果您添加它，它就不会编译。@EndeNeu这是一个疏忽。您是对的，它不会编译（如预期的那样）。我已经更新了这个问题，使它看起来尽可能接近真实的代码。当然，这没有用，因为上面的代码没有编译，我的代码也编译了。@muhuk如果上面的代码没有编译，那么它就不代表你的编译代码。除非你得到一个正确的最小示例，否则这个问题无法回答。好的。现在，上面的代码是does编译，据我所知，它不应该编译。这一定是一个bug。谢谢。但这不是答案。是的，我不知道如何在堆栈溢出上获得一个大的代码片段。
$ scala
Welcome to Scala 2.12.0-M5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_92).
Type in expressions for evaluation. Or try :help.

scala> :pa
// Entering paste mode (ctrl-D to finish)

sealed abstract class Bar

case object BarOne extends Bar

case object BarTwo extends Bar

sealed abstract class Foo {
  type A <: Bar

  def f: A
}

object Foo {
  object FooOne extends Foo {
    type A = BarOne.type
    val f = BarTwo
  }

  object FooTwo extends Foo {
    type A = BarTwo.type
    val f = BarOne
  }
}

// Exiting paste mode, now interpreting.

<console>:26: error: overriding method f in class Foo of type => Foo.FooOne.A;
 value f has incompatible type
           val f = BarTwo
               ^
<console>:31: error: overriding method f in class Foo of type => Foo.FooTwo.A;
 value f has incompatible type
           val f = BarOne
               ^

$ scala
Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_92).
Type in expressions for evaluation. Or try :help.

scala> object X ; object Y
defined object X
defined object Y

scala> class C { def f: X.type = X }
defined class C

scala> class D extends C { override def f: Y.type = Y }
defined class D

scala> :quit
$ scalam
Welcome to Scala 2.12.0-M5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_92).
Type in expressions for evaluation. Or try :help.

scala> scala> object X ; object Y

// Detected repl transcript. Paste more, or ctrl-D to finish.

defined object X
defined object Y

scala> class C { def f: X.type = X }
defined class C

scala> class D extends C { override def f: Y.type = Y }
defined class D
// Replaying 3 commands from transcript.

scala> object X ; object Y
defined object X
defined object Y

scala> class C { def f: X.type = X }
defined class C

scala> class D extends C { override def f: Y.type = Y }
<console>:13: error: overriding method f in class C of type => X.type;
 method f has incompatible type
       class D extends C { override def f: Y.type = Y }
                                        ^