斯卡拉-相互排斥的特性

Question

是否有一种方法可以定义公共类型的可选方案的集合：

trait Mutability
trait Mutable extends Mutability
trait Immutable extends Mutability

并让编译器排除如下内容：

object Hat extends Mutable with Immutable

我相信我可以通过有一个共同的、相互冲突的成员来强制一些编译器错误，但是错误信息有点偏斜：

trait Mutability
trait Mutable extends Mutability { protected val conflict = true }
trait Immutable extends Mutability { protected val conflict = true }

object Hat extends Mutable with Immutable

<console>:10: error: object Hat inherits conflicting members:
value conflict in class Immutable$class of type Boolean  and
value conflict in class Mutable$class of type Boolean
(Note: this can be resolved by declaring an override in object Hat.)
   object Hat extends Immutable with Mutable

有没有一种更直接的方式来表达这个约束，而不允许有人通过接受编译器提供的提示(在Hat中覆盖‘冲突’)来绕过它呢？

谢谢你的见解

Answer 1

我觉得这可能有用

sealed trait Mutability
case object Immutable extends Mutability
case object Mutable extends Mutability

trait MutabilityLevel[A <: Mutability]

class Foo extends MutabilityLevel[Immutable.type]

这个(ab？)使用的事实是，不能用不同的参数化两次扩展相同的特性。

scala> class Foo extends MutabilityLevel[Immutable.type] with MutabilityLevel[Mutable.type]
<console>:11: error: illegal inheritance;
 self-type Foo does not conform to MutabilityLevel[Immutable.type]'s selftype MutabilityLevel[Immutable.type]
       class Foo extends MutabilityLevel[Immutable.type] with MutabilityLevel[Mutable.type]
                         ^
<console>:11: error: illegal inheritance;
 self-type Foo does not conform to MutabilityLevel[Mutable.type]'s selftype MutabilityLevel[Mutable.type]
       class Foo extends MutabilityLevel[Immutable.type] with MutabilityLevel[Mutable.type]

但是..。

scala> class Foo extends MutabilityLevel[Mutability]
defined class Foo