Non null promotion fail in if( a != null ){...}

[rxlabz]

I maybe miss something but shouldn't the name property be promoted to NonNull in this example ? https://nullsafety.dartpad.dev/dcb8f17148eb07b1b7c36442eb2d53d7

In DartPad (Dart SDK 2.10.0), the analyzer feedback is : A value of type 'String?' can't be assigned to a variable of type 'String'.

class App {
  const App({this.name});

  final String? name;

  Map<String, dynamic> toJson() {
    final json = <String, String>{};

    if (name != null) {
      json['name'] = name;
    }
    return json;
  }
}

void main(){
  final app = App(name:'app');
  assert(app.toJson() == {"name":app});
}

[eernstg]

No, only local variables can be promoted. There are considerations about allowing instance variables to be promoted as well, but the current rules don't promote them. The main issue is that it is not sound to promote an instance variable, because it can be overridden by a getter running arbitrary code and that getter is not known to return the same object each time it is invoked.

[rxlabz]

Thanks, I'm closing it !

[eernstg]

Thanks! The topic is already covered by several existing issues, here's another one: dart-lang/language#1187.