ArrayBuffer_vs_ListBuffer

ArrayBuffer.scala

 class Foo {
    import scala.collection.mutable.ArrayBuffer
    val elements = List(1,2,3)
    def map[T](block: Int => T) = {
      val vals = ArrayBuffer[T]()
      elements foreach{ i => vals += block(i) }
      vals.toArray
    }
  }

// faild (scala-2.8.1)
error: could not find implicit value for evidence parameter of type ClassManifest[T]
      vals.toArray
           ^

ListBuffer.scala

 class Foo {
    import scala.collection.mutable.ListBuffer
    val elements = List(1,2,3)
    def map[T](block: Int => T) = {
      val vals = ListBuffer[T]()
      elements foreach{ i => vals += block(i) }
      vals.toList
    }
  }

// passed (scala-2.8.1)