[fpc-pascal] Proper preprocessor?

[Sven Barth]

Am 21.06.2018 um 17:25 schrieb Ryan Joseph:
>
>> On Jun 21, 2018, at 10:08 PM, Sven Barth via fpc-pascal <fpc-pascal at lists.freepascal.org> wrote:
>>
>> For more questions you can start a thread in fpc-devel. That's the purpose of that mailing list after all.
>>
> Thanks, I’ll post there tomorrow about the technical stuff.
>
> At first glance unless I totally underestimate something it appears to be a trivial extension to the define:= syntax but admittedly it’s edge case stuff and probably not widely used.
>
> I did a search and found only a few hits on the topic. Since I’ve been giving theoretical examples here’s something more practical a user attempted. Can you do that without macros? If I had to guess he had some funky code and just wanted to reduce typing and copy/paste bugs.
>
> {$define HOFFSET(rec,field) := pointer(@rec.field) - pointer(@rec)}
>
> type
>          s1_t = record
>                  a: longint;
>                  b: single;
>                  c: double;
>          end;
> var
>          s1: s1_t;
> BEGIN
>          s1.a := 12345;
>          s1.b := 1.000000001;
>          s1.c := 1.000000002;
>
>          writeln(HOFFSET(s1, a));
> END.

The officially sanctioned way is this:

@s1_t(nil^).a

Though I do have the idea to extend the Ofs() intrinsic to handle a type 
expression as well. E.g. Ofs(s1.a) returns @s1.a, but I'd like 
Ofs(s1_t.a) to return @s1_t(nil^).a.

Regards,
Sven