On Dec11, 2013, at 11:47 , Andres Freund <and...@2ndquadrant.com> wrote: > On 2013-12-11 11:42:25 +0100, Florian Pflug wrote: >> On Dec5, 2013, at 15:44 , Andres Freund <and...@2ndquadrant.com> wrote: >>> There might be some ugly compiler dependent magic we could do. Depending >>> on how we decide to declare offsets. Like (very, very roughly) >>> >>> #define relptr(type, struct_name, varname) union struct_name##_##varname{ \ >>> type relptr_type; \ >>> Offset relptr_off; >>> } >>> >>> And then, for accessing have: >>> #define relptr_access(seg, off) \ >>> typeof(off.relptr_type)* (((char *)seg->base_address) + off.relptr_off) >>> >>> But boy, that's ugly. >> >> Well, uglyness we can live with, especially if it's less ugly than the >> alternatives. But I'm afraid is also unportable - typeof() is a GCC >> extension, not a part of ANSI C, no? > > Yes (although there's C11 stuff to do equivalent stuff afair) - I was > thinking of only doing it for compilers we support that dark magic for > and fall back to returning a void* for the others. We'll probably miss a > cast or two required on !gcc that way, but it's still likely to be less > error prone.
Would it? For this to catch type mismatches, you'd both need to develop on a typeof-supporting compiler *and* don't cast the result of relptr_access(). But you can't really do that, because the code will then fail on compilers which don't support typeof()... What we could do, I guess, is to pass the type to relptr_access() and to relptr(), and let the compiler verify that they are the same. Something like #define relptr(type) union { \ type relptr_type; \ Offset relptr_off; \ } #define relptr_access(type, seg, rptr) \ (type)( \ (rptr.relptr_type - (type)0), \ ((char*)seg->base_address) + rptr.relptr_off \ ) And, yes, ouch ;-) best regards, Florian Pflug -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers