Demonstrate anonymous class nesting from Iterator drop method

drop_test.scala

import java.io.{StringWriter, PrintWriter}
import scala.reflect.ClassTag

def tracehead(e: Exception, substr: String = "slice"): String = {
  val sw = new StringWriter()
  e.printStackTrace(new PrintWriter(sw))
  sw.toString.split('\n').takeWhile((s:String)=> !s.contains(substr)).drop(1).mkString("\n")  
}

class TestIterator[T: ClassTag](val iter: Iterator[T]) extends Iterator[T] {
  override def hasNext = iter.hasNext
  override def next = {
    println(tracehead(new Exception))
    iter.next
  }
}

def drop_test[T](itr: Iterator[T]) {
  var n = 0
  var iter = itr
  while (iter.hasNext) {
    n += 1
    println(s"\ndrop # $n")
    iter = iter.drop(1)
  }
}