我试图用抽象成员覆盖一个特征成员,这看起来很简单,但实际上不会编译。
以下是我正在尝试执行的操作的归结示例:
// not my code:
trait Base {
val x = new T {}
trait T {}
}
// my code:
trait Sub extends Base {
// compile error; see below
override val x: T2
// this compiles, but doesn't force `Impl` to implement `x`
// override val x: T2 = null
trait T2 extends T {
val someAddition: Any
}
}
object Impl extends Sub {
// should be forced to implement `x` of type `T2`
}
这是编译器错误:
Error:(7, 7) overriding value x in trait Sub of type Sub.this.T2;
value x in trait Base of type Sub.this.T has incompatible type;
(Note that value x in trait Sub of type Sub.this.T2 is abstract,
and is therefore overridden by concrete value x in trait Base of type Sub.this.T)
trait Sub extends Base {
^
我能想到的一种技术是为抽象成员使用不同的名称,并让具体成员调用这个名称。
trait Sub extends Base {
val y: T2
override val x = y
在爪哇土地上有一个有趣的讨论。