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?

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

On Monday, 10 October 2016 at 18:21:10 UTC, Jonathan M Davis wrote:
> On Monday, October 10, 2016 17:57:15 Satoshi via Digitalmars-d-learn wrote:
>> [...]
>
> 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



Thanks a lot!