Linearization of traits in Scala to handle the diamond inheritance problem. Adapted from http://jim-mcbeath.blogspot.co.uk/2009/08/scala-class-linearization.html It now seems OK to refer to indirect parent traits, i.e. super[A], which apparently wasn't possible at the time of the original article.

diamond.scala

// Adapted from http://jim-mcbeath.blogspot.co.uk/2009/08/scala-class-linearization.html

object diamond {
  class A { def t = 1 }
  
  // super refers to the next trait in the linearization, not necessarily to A
  trait B extends A { override def t = super.t + 1 }
  trait C extends A { override def t = super.t * 2 }

  // Linearises to (D1, C, B, A)
  class D0 extends B with C
  class D1 extends B with C { override def t = super.t } // C
  class D2 extends B with C { override def t = super[A].t }
  class D3 extends B with C { override def t = super[B].t }
  class D4 extends B with C { override def t = super[C].t }
  class D5 extends B with C { override def t = 5 }

  // Linearises to (D1, B, C, A)
  class E0 extends C with B
  class E1 extends C with B { override def t = super.t } // B
  class E2 extends B with C { override def t = super[A].t }
  class E3 extends C with B { override def t = super[B].t }
  class E4 extends C with B { override def t = super[C].t }
  class E5 extends C with B { override def t = 5 }

  println((new D0).t)                             //> 4
  println((new D1).t)                             //> 4
  println((new D2).t)                             //> 1
  println((new D3).t)                             //> 2
  println((new D4).t)                             //> 4
  println((new D5).t)                             //> 5

  println((new E0).t)                             //> 3
  println((new E1).t)                             //> 3
  println((new E2).t)                             //> 1
  println((new E3).t)                             //> 3
  println((new E4).t)                             //> 2
  println((new E5).t)                             //> 5
}