Simple Singleton

main.dart

class Singleton {
  
  int _counter;
  
  static final Singleton _instance = Singleton._internal();
  factory Singleton()=> _instance;
  Singleton._internal() {
    _counter = 0;
  }
  
  void counterUp() => _counter +=1;
  String get counter => _counter.toString();
}


void main() {
  Singleton _first = Singleton();
  Singleton _second = Singleton();
  
  for(int i=0;i < 5;i++){
    _first.counterUp();
    print(_second.counter);
  }
}