// from any read operation.)
func (b *Buffer) UnreadRune() error {
	if b.lastRead <= opInvalid {
		return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
	}
	if b.off >= int(b.lastRead) {
		b.off -= int(b.lastRead)
	}
	b.lastRead = opInvalid
	return nil
}

      }
    } finally {
      readCompleteLatch.countDown()
    }
  }

  abstract fun listSource(): Source

  override fun ensureLoaded() {
    if (!listRead.get() && listRead.compareAndSet(false, true)) {
      readTheListUninterruptibly()
    } else {
      try {
        readCompleteLatch.await()
      } catch (_: InterruptedException) {

      Pray how did you manage to do it?'

    `In my youth,' said his father, `I took to the law,
      And argued each case with my wife;
    And the muscular strength, which it gave to my jaw,
      Has lasted the rest of my life.'

    `You are old,' said the youth, `one would hardly suppose
      That your eye was as steady as ever;
    Yet you balanced an eel on the end of your nose--