std::tuple, get item by inherited type

In c++11 I have very neat and working code for extracting std::tuple item by type (As I know this feature even placed to c++14 stl)

Now I'm facing with the task to select item by the inherited class specification

 struct A
 {
     int a;
 };
 struct B : public A
 {
     int b;
 };

 ...
 auto tval = std::make_tuple(1, B());
 //now I would like to reference items as following:
 tuple_ref_by_inheritance<A>(tval).a = 5; //Access to B instance by parent A

Following code is my unsuccessful try:

    template< class T, class Tuple >
    struct tuple_ref_index;

    // recursive case
    template<class T, class Head, class... Tail >
    struct tuple_ref_index<T, std::tuple<Head, Tail...> >  
    { 
        enum { value = tuple_ref_index<T, std::tuple<Tail...>>::value + 1 };
    };

    template<class T, class Head, class... Tail >
    struct tuple_ref_index<T, std::tuple<Head, Tail...> >  
    { 
        const static typename std::enable_if<
              std::is_same<T, Head>::value>::type* _= nullptr;
        enum { value = 0 };
    };

    template <class T, class Tuple>
    inline T& tuple_ref_by_inheritance(Tuple& tuple)
    {
        return std::get< tuple_ref_index<T, Tuple>::value >(tuple);
    }