How to use scala trait with `self` reference?

Question

I saw some code write trait as following:

trait SelfAware { self: Self =>
 ....
}

class Self
val s = new Self with SelfAware // this is ok
println(s.self         


        

Answer 1

To answer the other half of your question (why does println(s.self) produce an error?), that is because self is not a field of SelfAware. It can be used to define such fields, however:

trait SelfAware { self =>
  val me = self
}

class X
val x = new X with SelfAware
println(s.me)