Dart: Delegate the comparison operator of a derived class to comparison operator of base class

I want to overload the the comparison operator (==) in Dart to compare structures. Now I'm not sure how to do this for derived classes when I already have overloaded the comparison operator of the base class and want to reuse that.

Assuming I have a a base class like:

class Base
{
  int _a;
  String _b;

  bool operator ==(Base other)
  {
    if (identical(other, this)) return true;
    if (_a != other._a) return false;
    if (_b != other._b) return false;
    return true;
  }
}

Then I declare I derived class that adds additional fields and also want to overload operator==. I only want to compare the additional fields in the derived class and delegate the comparison of Base fields to the Base class. In other programming languages I could do something like Base::operator==(other) or super.equals(other), but in Dart I can't figure out what's the best way to do it.

class Derived extends Base
{
  int _c; // additional field

  bool operator ==(Derived other)
  {
    if (identical(other, this)) return true;        
    if (_c != other._c) return false; // Comparison of new field

    // The following approach gives the compiler error:
    // Equality expression cannot be operand of another equality expression.
    if (!(super.==(other))) return false;

    // The following produces "Unnecessary cast" warnings
    // It also only recursively calls the Derived operator
    if ((this as Base) != (other as Base)) return false;    

    return true;
  }
}

I guess what I could do is:

• Compare all fields of base class also in the derived class: Is very error prone if base class get's changed and also doesn't work when base and derived are in different packages.
• Declare an equals function with the same logic as currently operator == in it, call super.equals() to compare the base class and delegate all calls of operator== to the equals function. However it doesn't look too appealing to implement equals and operator ==.

So what's the best or recommended solution for this problem?