main.dart

// SO 29334843

main() {
  var a = new A()..doSomething();
  print('`a:` $a');
  var b = new B()..doSomething();
  print('`b:` $b');
  var c = new C()..doSomething();
  print('`c:` $c');
}

abstract class A {
  void doSomething() => print('Do something..');
  factory A() => new B();
  A.protected();
}

class B implements A {
  @override
  void doSomething() => print('Do something already..');
}

class C extends A {
  C() : super.protected();
}