Kotlin 中的部分类委托

如何在Kotlin中对方法/字段进行部分委托？

具体来说:这里我试图从接口TraitA继承类User，并在包装器StateA中实现字段marked: Boolean.这将清理User实现，因为marked只是一个状态字段.注意TraitA不能是一个类，因为我想使用几个这样的接口:User() : TraitA by StateA, TraitB by StateB, ..

/* does not compile (Kotlin M12) */
interface TraitA {
    var marked: Boolean

    fun doStaffWithMarked()  // must be overridable
}

class StateA() : TraitA {
    override var marked = false
}

class User() : TraitA by StateA(){
    override fum doStaffWithMarked() {
        //...all fancy logic here...
    }
}

The alternative is to implement all in one place:

class User() : TraitA{
    override var marked = false // ugly code

    override fum doStaffWithMarked() {
        //...
    }
}

Is there a way/pattern that would solve that problem with easy and as little code as possible? Code/bytecode generation is not an option for me.

UPDATE

我对此不是很清楚，但请注意，每User人中有doStaffWithMarked()人是unique人.

So I may suggest a 'half-bad' solution with run-time assertions:

interface TraitA {
    var marked: Boolean

    /* must be overridden */
    fun doStaffWithMarked() = throw UnsupportedOperationException()
}

class StateA() : TraitA {
    override var marked = false
}

class User() : TraitA by StateA() {
    override fum doStaffWithMarked() {
        //...all fancy logic here...
    }
}

The question is still open, since a really good solution would check that doStaffWithMarked() at compilation time.