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

A self type lets you specify what types are allowed to mixin a trait. For example, if you have a trait with a self type Closeable, then that trait knows that the only things that are allowed to mix it in, must implement the Closeable interface.