what is the self => used for? [duplicate]

Question

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

When i look in to the source code of: scala/src/library/scala/Option.scala

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

I wander what the self use for. I know the normal use of self type is to restrict the class the trait can be mixed in. such as:

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>

but the "this =>" is not the case. what indeed this "this =>" used for?

Answer 1

It creates an alias to this, which may be handy in inner classes (synonymous for OuterClass.this)

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