Singleton with Dart lang

main.dart

void main() {
  
  Singleton singleton1 = new Singleton();
  Singleton singleton2 = new Singleton();
  
  print(identical(singleton1, singleton2));
  
  print(TrueSingleton.getInstance());
}

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

class TrueSingleton {
  
  static final TrueSingleton _singleton = new TrueSingleton._internal();
  
  TrueSingleton._internal();
  
  static TrueSingleton getInstance() => _singleton;
}