scala - self => 是用来做什么的？

Question

这个问题已经有答案了:

已关闭 11 年前。

Possible Duplicate:
What does “outer =>” really mean?

当我查看以下源代码时:scala/src/library/scala/Option.scala

sealed abstract class Option[+A] extends Product with Serializable {
  self =>

我想知道 self 有什么用。我知道 self 类型的正常用途是限制可以混合特征的类。例如:

scala> trait A
defined trait A

scala> trait NeedA {self: A =>}
defined trait NeedA

scala> new NeedA {}
<console>:10: error: illegal inheritance;
 self-type java.lang.Object with NeedA does not conform to NeedA's selftype NeedA with A
              new NeedA {}
                  ^

scala> new NeedA with A {}
res39: java.lang.Object with NeedA with A = $anon$1@4d04a0e8

scala>

但“this =>”并非如此。这个“this =>”到底是用来做什么的？

Answer 1

它创建了一个别名，这在内部类中可能很方便(与 OuterClass.this 同义)

class A {self => 
   ...
  class B {
      // self is the enclosing A, synonymous for A.this
  }
}