dCircularBuffer;
    this.head.push(data);
  }
  shift() {
    let tail = this.tail, next = tail.shift();
    if (tail.isEmpty() && tail.next !== null)
      this.tail = tail.next, tail.next = null;
    return next;
  }
}
$ = {
  FixedCircularBuffer,
  FixedQueue
};
return $})