Strange Dart 9 (2)

main.dart

import 'my_library.dart';

// Same class B in Strange Dart 9.1, but this time it's accepted.
class B implements A {}

void main() {
  wat(B()); // _a getters and setters redirect to noSuchMethod
}

my_library.dart

// Same definition in Strange Dart 9.1.
class A {
  int _a = 1;
  int _b = 2;

  @override
  String toString() => '$_a $_b';
}

void wat(A a) {
  print(a._a); // subtypes need to have getter _a
  a._a = 123; // subtypes need to have setter _a
}