library test;

typedef void F<T>(T x);

class B<T> {
  B<T> operator +(B<T> other) => throw '';
}

class C<T> {
  B<F<T>> get x => throw '';
  void set x(B<F<T>> value) {}
  B<F<T>>? get x2 => null;
  void set x2(B<F<T>>? value) {}
}

void test(C<num> c) {}
main() {}