Question

It seems I can use self or this for referring to the mixed-in instance or rather to constraint the mixed-in instance. For instance, are those equivalent?

scala> trait A { self: List[_] => }
defined trait A

scala> trait B { this: List[_] => }
defined trait B

Is this just a convention, or using something different than this provide some benefits?

Answer 1

Using a name other than “this” can be useful where you have member types which refer to the enclosing instance. For example,

trait Outer { self =>
  trait Inner {
    def outer = self
  }
}

is preferable to,

trait Outer {
  trait Inner {
    def outer = Outer.this
  }
}

in some circumstances.