struct BaseA {
   Array<int> a;
   auto& BaseARef() { return *this; }
};

struct BaseB {
   BaseA& baseA;

   BaseB(BaseA& baseA) : baseA(baseA) {
      // do something with baseA.a;
   }
};

struct Whatever : BaseA, BaseB {
    Whatever() : BaseA(), BaseB(BaseARef()) {} 
};