class A {
  double? foo1;
  String? foo2;
  int foo3 = 0;
  void operator []=(bool key, String? value) {}
  String? operator [](bool key) => "";
}

class B extends A {
  test() {}
}

extension E on dynamic {
  void operator []=(String key, int? value) {}
  int? operator [](String key) => 0;
}

main() {}