Domino Timer

main.dart

import 'dart:async';

class Singleton {
  static final _instance = Singleton._internal();
  factory Singleton() => _instance;
  Singleton._internal() {}
  
  Duration _delay = Duration();
  Timer _reset;
  void _timeout() => _delay = Duration();
  
  Duration delay(Duration duration) {
    if(_reset== null||!_reset.isActive) {
      _reset = Timer(duration,_timeout,);
    }
    return _delay+=duration;
  }
}

void main() async {
  const Duration _duration = Duration(milliseconds:200); 
  final Singleton _singleton = Singleton();
  
  for(int i=1;i <= 10;i++){
    await Future.delayed(_singleton.delay(_duration));
    print(i.toString());
  }
}