// @dart = 2.6
class A<T> {
  A(this.x);
  _X<T> x;
}

class B<T> extends A<T> {
  B() : super(const _X());
}

class _X<T> {
  const factory _X() = _Y<T>;
}

class _Y<T> implements _X<T> {
  const _Y();
}

main() {}