What is the difference between self-types and trait subclasses?

Question

A self-type for a trait A:

trait B
trait A { this: B => }

says that \"A cannot be mixed into a concrete cl

Answer 1

Another thing that has not been mentioned: because self-types aren't part of the hierarchy of the required class they can be excluded from pattern matching, especially when you are exhaustively matching against a sealed hierarchy. This is convenient when you want to model orthogonal behaviors such as:

sealed trait Person
trait Student extends Person
trait Teacher extends Person
trait Adult { this : Person => } // orthogonal to its condition

val p : Person = new Student {}
p match {
  case s : Student => println("a student")
  case t : Teacher => println("a teacher")
} // that's it we're exhaustive