class MyClass {
  static final MyClass _singleton = new MyClass._internal();

  factory MyClass() {
    return _singleton;
  }

  MyClass._internal() {
    ... // initialization logic here
  }

  ... // rest of the class
}

// consuming code
MyClass myObj = new MyClass(); // get back the singleton
...
// another piece of consuming code
MyClass myObj = new MyClass(); // still getting back the singleton