package Main

abstract class Buffer{
  type T
  val element: T
}

abstract class SeqBuffer extends Buffer{
  type U
  type T <: Seq[U]
  def length = element.length
}

abstract class IntSeqBuffer extends SeqBuffer{
  type U = Int
}

object AbstractTypeTest1 extends App{
  def newIntSeqBuf(elem1: Int, elem2: Int): IntSeqBuffer =
    new IntSeqBuffer{
	  type T = List[U]
	  val element = List(elem1, elem2)
  }
  val buf = newIntSeqBuf(7, 8)
  println("length = " + buf.length)
  println("content = " + buf.element)
}

abstract class Buffer2[+T] {
  val element: T
}

abstract class SeqBuffer2[U, +T <: Seq[U]] extends Buffer2[T] {
  def length = element.length
}

object AbstractTypeTest2 extends App {
  def newIntSeqBuf(e1: Int, e2: Int): SeqBuffer2[Int, Seq[Int]] =
    new SeqBuffer2[Int, List[Int]] {
      val element = List(e1, e2)
    }
  val buf = newIntSeqBuf(7, 8)
  println("length = " + buf.length)
  println("content = " + buf.element)
}