LookBehindIterator.scala

object LookBehindIterator {

  trait LookBehindIterator[+A] extends Iterator[A] {
    def last: A
    def lastOption: Option[A] = Option(last)
  }

  implicit class ImplicitLookBehindIterator[T](val it: Iterator[T]) extends AnyVal {
    def lookBehind: LookBehindIterator[T] =
      new scala.collection.AbstractIterator[T] with LookBehindIterator[T] {
        private[this] var lastHd: T = _
        def last: T                 = lastHd
        def hasNext: Boolean        = it.hasNext
        def next(): T = {
          lastHd = it.next()
          lastHd
        }
      }
  }
}