gistfile1.scala

trait Example { self =>
  def mode(m: String): self.type
}

case class Foo extends Example {
  def mode(m: String) = this.copy(mode = m)
}


// abstract type, polymorhpic

trait Example[A] {
  def mode(m: String): A
}

case class Foo extends Example[Foo] {
  def mode(m: String) = this.copy(mode = m)
}


// abstract type, implementation

trait Example {
  type A
  def mode(m: String): A
}

case class Foo extends Example {
  type A = Foo
  def mode(m: String) = this.copy(mode = m)
}