Kotlin 中密封类之外的引用? [英] Reference outside the sealed class in Kotlin?

问题描述

我正在尝试创建一个类，该类使用自己的状态来操作它持有引用的外部对象的状态.外部对象可以是A类或B类，两者相似，但不受作者控制.因此，根据 @SimY4 的早期答案，创建了一个密封类来访问它们的公共属性.

I'm trying to create a class that uses its own state to operate on the state of an external object that it holds a reference to. The external object can be of class A or B, which are similar, but not controlled by the author. So a sealed class is created to access their common attributes, per this earlier answer from @SimY4.

// *** DOES NOT COMPILE ***
class A {   // foreign class whose structure is not modifiable
  val prop get()= "some string made the Class-A way"
}
class B {   // foreign class whose structure is not modifiable
  val prop get()= "some string made the Class-B way"
}
data class ABTool (val obj:AB, val i:Int, val j:Int) {
  // class that manipulates i and j and uses them to do
  // things with AB's "common" attributes through the sealed class AB
  sealed class AB {   // substitute for a common interface
    abstract val prop: String
    abstract val addmagic: String
    data class BoxA(val o:A) : AB() {
      override val prop get()= o.prop
      override val addmagic get() = prop + this@???.magic  // HOW TO REFERENCE?
    }
    data class BoxB(val o:B) : AB() {
      override val prop get()= o.prop
      override val addmagic get() = this@???.magic + prop  // HOW TO REFERENCE?
    }
  }
  val magic get()= "magic: ${i*j}"
}

现在的问题是我发现我不能以我想要的方式操作外部对象，因为密封类不能引用它的外部类成员.有没有更好的方法来完成这项工作，即使使用不同的方法(密封类除外)，同时:

The problem now is that I've figured out I can't operate on the external object in the way I want, because a sealed class can't refer to its outer class members. Is there a better way to make this work, even if using a different approach (other than sealed class), while:

• 不改变外国A类或B类；
• 考虑到 A 和 B(以及实际情况中的许多其他人)是相似的，所以我正在尝试编写一个工具，使用相同的代码库来计算 A 和 B 并为 A 和 B 添加魔法；和
• 请注意，虽然 ABTool 工具是相同的，但它们用于添加魔法的方式在 A 和 B 中略有不同，就像访问 A 和 B 的概念上常见元素的方式可能不同.

对此或类似的解决方法有什么想法吗?也许我还没有想到更实用的方法?

Any thoughts on this or a similar workaround? Maybe a more functional approach that I haven't conceived yet?

推荐答案

如果 ABTool 作为一个密封类是你可以放弃的，那么这里有一个解决方案:

If ABTool being a sealed class is something you can give up, then here's a solution:

1. 在ABTool声明中用inner abstract替换sealed；
2. 将BoxA 和BoxB 标记为inner；

1. Replace sealed with inner abstract at the ABTool declaration;
2. Mark BoxA and BoxB as inner as well;

data class ABTool(val obj: AB, val i: Int, val j: Int) {
    inner abstract class AB {
        abstract val prop: String
        abstract val addmagic: String

        inner class BoxA(val o: A) : AB() {
            override val prop get() = o.prop
            override val addmagic get() = prop + magic
        }

        inner class BoxB(val o: B) : AB() {
            override val prop get() = o.prop
            override val addmagic get() = magic + prop
        }
    }

    val magic get() = "magic: ${i * j}"
}

(或者，不是将 AB 标记为内部，而是将 BoxA 和 BoxB 移出它到 ABTool<的范围内/code>)

(alternatively, instead of marking AB as inner, move BoxA and BoxB out of it to the scope of ABTool)

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