ptrdiff_t of class.tupleof entry

[Satoshi via Digitalmars-d-learn]

Hello,
How can I take an ptrdiff_t of any tupleoff entry from class 
during compilation?


I need something like this:

template Test(T, int i) {
  enum Test = &T.tupleof[i] - &T.tupleof[0];
}


and then use it like:

class AnyClass {
int a;
int b;
int c;
string d;

}

enum Addr = Test!(AnyClass, 3);

void assignInt!(T)(AnyClass cls, T value) {
*(cast(T *)cast(void *)cls + Addr) = value;
}



This is just an example how I need to use it.
Is something like this possible to do?