1 package Main

     2 

     3 abstract class Buffer{

     4   type T

     5   val element: T

     6 }

     7 

     8 abstract class SeqBuffer extends Buffer{

     9   type U

    10   type T <: Seq[U]

    11   def length = element.length

    12 }

    13 

    14 abstract class IntSeqBuffer extends SeqBuffer{

    15   type U = Int

    16 }

    17 

    18 object AbstractTypeTest1 extends App{

    19   def newIntSeqBuf(elem1: Int, elem2: Int): IntSeqBuffer =

    20     new IntSeqBuffer{

    21 	  type T = List[U]

    22 	  val element = List(elem1, elem2)

    23   }

    24   val buf = newIntSeqBuf(7, 8)

    25   println("length = " + buf.length)

    26   println("content = " + buf.element)

    27 }

    28 

    29 abstract class Buffer2[+T] {

    30   val element: T

    31 }

    32 

    33 abstract class SeqBuffer2[U, +T <: Seq[U]] extends Buffer2[T] {

    34   def length = element.length

    35 }

    36 

    37 object AbstractTypeTest2 extends App {

    38   def newIntSeqBuf(e1: Int, e2: Int): SeqBuffer2[Int, Seq[Int]] =

    39     new SeqBuffer2[Int, List[Int]] {

    40       val element = List(e1, e2)

    41     }

    42   val buf = newIntSeqBuf(7, 8)

    43   println("length = " + buf.length)

    44   println("content = " + buf.element)

    45 }