verificar password flutter stream

Stream<bool> get registerValid => Observable.combineLatest3(
  email, 
  password, 
  confirmPassword, 
  (e, p, c) => (0 == p.compareTo(c))
);

Stream<String> get confirmPassword => 
  _passwordConfirmController.stream.transform(validatePassword)
    .doOnData((String c){
      // If the password is accepted (after validation of the rules)
      // we need to ensure both password and retyped password match
      if (0 != _passwordController.value.compareTo(c)){
        // If they do not match, add an error
        _passwordConfirmController.addError("No Match");
      }
    },
  );