Here I have an enum defined as:

enum Routes<T, R> {
  home(
    name: '/home',
    fromJson: HomeRouteArguments.fromJson,
    navigate: navigateToHome,
  ),

  const Routes({
    required this.name,
    required this.navigate,
    this.fromJson,
    this.additionalNames = const [],
  });

  final String name;
  final List<String> additionalNames;
  final T? Function(Map<dynamic, dynamic>)? fromJson;
  final R? Function(BuildContext context, {required T args}) navigate;
}

Future<void> navigateToHome(BuildContext context,
    {required  HomeRouteArguments? args}) async {
    //... stuff
}

HomeRouteArguments.fromJson is just a named constructor of the HomeRouteArguments class.

I intend for the route arguments to always be supplied but optionally null. So for example:

Routes.home.navigate(context, args: null);

Because the named constructor returns a non-nullable type, it then sets the generic to that non-nullable type. So when I use the method it requires args to be a non-null value. When I don’t supply the fromJson parameter however it works just as I intend.

Help would be appreciated.

Making the return type of the fromJson nullable doesn’t seem to fix it (as I have put in this example). Currently the
only thing I can do is remove the return type from the fromJson parameter but I would rather have the type there for safety.

Setting the generic values when initializing the values doesn’t work either.