Flutter simple productFlavors

Draft

Without productFlavors:

main.dart:

void main() async {
  runApp(MyApp(key: appKey));
}
class MyApp extends StatelessWidget {
  Widget build(context) => MaterialApp(
    // ...
  );
}

With productFlavors:

flutter build apk -t lib/main.dev.dart --flavor dev

main.dev.dart:

void main() async {
  R.initialize(R$Dev());
  runApp(MyApp());
}

app.dart:

class MyApp extends StatelessWidget {
  Widget build(context) => MaterialApp(
    // ...
    body: Text(R.of.api_base_url)
  );
}

r.dart:

class R {
  String get api_base_url => "http://example.com/";

  static R _current;
  static void initialize(R value) => _current = value;
  static R get of {
    _current ??= R();
    return _current;
  }
}

r.dev.dart:

class R$Dev extends R {
  @override
  String get api_base_url => "http://dev.example.com/";
}