dart singletons

dart.dart

// fancy constructor way
class SingletonOne {

  SingletonOne._privateConstructor();

  static final SingletonOne _instance = SingletonOne._privateConstructor();

  factory SingletonOne() {
    return _instance;
  }

}

// static field with getter
class SingletonTwo {

  SingletonTwo._privateConstructor();

  static final SingletonTwo _instance = SingletonTwo._privateConstructor();

  static SingletonTwo get instance => _instance;
  
}

// static field
class SingletonThree {

  SingletonThree._privateConstructor();

  static final SingletonThree instance = SingletonThree._privateConstructor();
  
}