forexp.scala

scala> import scala.collection.mutable.ArrayBuffer
import scala.collection.mutable.ArrayBuffer

scala> case class CustomList[A](elements: A*) {
     | 
     |   val elems = new ArrayBuffer[A]
     |   elems ++= elements
     | }
defined class CustomList

scala> val list = CustomList(1, 2, 3)
list: CustomList[Int] = CustomList(WrappedArray(1, 2, 3))

scala> for( i <- list) { println(i) }
<console>:14: error: value foreach is not a member of CustomList[Int]
       for( i <- list) { println(i) }