main.dart

abstract class A {
  @override
  bool operator ==(dynamic other);
}

class B implements A {}

void test(dynamic x, dynamic y, dynamic z) {
  print(x == y || x == z);
}

void main() {
  var b1 = B(), b2 = B();
  B? b3;
  print(b1 == null);
  print(b1 == b2);
  print(b3 == b2);
  print(b3 == null);
  test(b1, b2, b3);
}