ptrdiff_t of class.tupleof entry

[Jonathan M Davis via Digitalmars-d-learn]

On Monday, October 10, 2016 17:57:15 Satoshi via Digitalmars-d-learn wrote:
> 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?

You can use the offsetof property of a member variable to find out the
offset between its address and the address of the beginning of the class or
struct that it's a member of.

- Jonathan M Davis