srecord TimestampRange(Timestamp start, Timestamp end) {
  *(long start, long end) {
    this(Timestamp(start), Timestamp(end));
  }
  
  Timestamp start() { ret start; }
  Timestamp end() { ret end; }
  
  selfType start aka startTime(Timestamp start) { this.start = start; this; }
  selfType end aka endTime(Timestamp end) { this.end = end; this; }
  
  bool complete() { ret start != null && end != null; }
  
  Duration duration() { ret !complete() ? null : end.minusAsDuration(start); }
}