[Dart Singleton] Different ways to have a singleton in Dart #singleton

factory-singleton.dart

class Singleton {
  	
  Singleton._internal();
  
  static final Singleton _singleton = new Singleton._internal();
  
  factory Singleton() => _singleton;
}

top-level-singleton.dart

final singleton = new Singleton._internal();

class Singleton {
  
  Singleton._internal();
  
}