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)

}