引用Scala中内部类的类型 [英] Referring to the type of an inner class in Scala

问题描述

以下代码试图模仿 DSL的多态嵌入:而不是在Inner中给出行为，而是在其封闭类的useInner方法中对其进行编码.我添加了enclosing方法，以便用户仅需保留对Inner实例的引用，但始终可以获取其封闭的实例.这样，特定Outer实例中的所有Inner实例都只绑定到一种行为(但是在这里需要这样做).

The following code tries to mimic Polymorphic Embedding of DSLs: rather than giving the behavior in Inner, it is encoded in the useInner method of its enclosing class. I added the enclosing method so that user has only to keep a reference to Inner instances, but can always get their enclosing instance. By doing this, all Inner instances from a specific Outer instance are bound to only one behavior (but it is wanted here).

abstract class Outer {
  sealed class Inner {
    def enclosing = Outer.this
  }
 def useInner(x:Inner) : Boolean
}

def toBoolean(x:Outer#Inner) : Boolean = x.enclosing.useInner(x)

它无法编译，scala 2.8抱怨:

It does not compile and scala 2.8 complains about:

type mismatch; found: sandbox.Outer#Inner
               required: _81.Inner where val _81:sandbox.Outer

来自编程Scala:嵌套类和

From Programming Scala: Nested classes and A Tour of Scala: Inner Classes, it seems to me that the problem is that useInnerexpects as argument an Inner instance from a specific Outer instance.

什么是真正的解释以及如何解决此问题?

What is the true explanation and how to solve this problem ?

推荐答案

我想Inner类型就像this.Inner类型. Outer#Inner独立于外部实例(不是依赖于路径的类型).

I suppose the type Inner is like the type this.Inner. Outer#Inner is independent of the outer instance (not a path-dependent type).

abstract class Outer {
  sealed class Inner {
    def enclosing = Outer.this
  }
  def useInner(x:Outer#Inner) : Boolean
}

def toBoolean(x:Outer#Inner) : Boolean = x.enclosing.useInner(x)

这篇关于引用Scala中内部类的类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！