== asymmetry demo

asymmetry.dart

class ThisClass {
  int bar;
  ThisClass(this.bar);
  @override
  bool operator ==(other) => other is ThisClass && other.bar == bar;
}

class ThatClass extends ThisClass {
  ThatClass(int bar, this.bob) : super(bar);
  int bob;

  @override
  bool operator ==(other) =>
      other is ThatClass && other.bob == bob && super == (other);
}
// ...

void main() {
  print(ThatClass(1, null) == ThisClass(1)); // false, good
  print(ThisClass(1) == ThatClass(1, null)); // true, oops
}