content.scala

    trait Box {
      type T
      private var t: T = _
      def put(t: T) = this.t = t
      def get = t
    }
    
    { // traits only
      trait IntBox extends Box { override type T = Int }
      val intBox = new IntBox {}
      intBox.put(1)
      val t = intBox.get // inferred: Int

      def extract(box: Box): box.T = box.get

      val got = extract(intBox) // inferred: Int
    }
    
    { // class IntBox
      class IntBox extends Box { override type T = Int }
      val intBox = new IntBox {}
      intBox.put(1)
      val t = intBox.get // inferred: intBox.T

      def extract(box: Box): box.T = box.get

      val got = extract(intBox) // inferred: intBox.T
    }