java - Kotlin中如何限制内部类的实例化仅在外部内部？

Question

拥有内部类和外部类，我想仅通过外部类的范围来限制内部类的实例化。我怎样才能在 Kotlin 中实现这一目标？ Java 以一种非常简单的方式提供了它。但似乎在 Kotlin 中我什至无法从内部类访问私有(private)字段。

Kotlin 拥有什么:

class Outer {
    val insideCreatedInner: Inner = Inner()
    inner class Inner
}

val insideCreatedInner = Outer().insideCreatedInner // Should be visible and accessible
val outsideCreatedInner = Outer().Inner() // I want to disallow this

Java 如何解决这个问题:

class Outer {
    Inner insideCreatedInner = new Inner();
    class Inner {
        private Inner() {}
    }
}

Outer.Inner insideCreatedInner = new Outer().insideCreatedInner;
Outer.Inner outsideCreatedInner = new Outer().new Inner(); // 'Inner()' has private access in 'Outer.Inner'

Answer 1

已编辑:要使 val 字段可见并同时隐藏 Inner 构造函数，使用接口(interface)可能会很有用这是可见的并使实现私有(private):

class Outer {
    val insideInner: Inner = InnerImpl()

    interface Inner {
        // ...
    }
    private inner class InnerImpl : Inner {
        // ...
    }
}


val outer = Outer()
val outsideInner = outer.InnerImpl() // Error! Cannot access '<init>': it is private in 'Inner'