Singleton pattern using Google Flutter Dart language

Singleton pattern is the design pattern to return only 1 instance of a class. 

class Store {

  static final Store _singleton = Store._internal();
  List<Order> list = new List<Order>();

  factory Store() {
    return _singleton;
  }

  Store._internal();

  addOrder(Order order){
    list.Add(order);
  }
}

To make a call to a function inside the singleton class:

Store().addOrder(order);