On Thu, Apr 30, 2009 at 9:13 PM, Carsten Haitzler <ras...@rasterman.com> wrote: > On Thu, 30 Apr 2009 18:02:45 -0300 Gustavo Sverzut Barbieri > <barbi...@profusion.mobi> said: > >> On Thu, Apr 30, 2009 at 10:11 AM, Albin Tonnerre >> <albin.tonne...@gmail.com> wrote: >> > Hello, >> > >> > While playing with Eina_Inlist, I noticed that given a pointer to an >> > Eina_Inlist, one can't easily get a pointer to the structure containing it. >> > The only option now is to put the Eina_Inlist first in the structure, and >> > then cast this structure to an Eina_Inlist, which is far from optimal. >> > I'd therefore like to propose that we add in eina_inlist.h a macro along >> > the >> > lines of >> > >> > #define FIND_A_SENSBILE_NAME_FOR_THIS(ptr, type) ((type *) ((Eina_Inlist *) >> > #ptr - offsetof(type, __in_list))) >> > >> > Then, we could get a pointer to the containing structure, no matter where >> > the Eina_Inlist is (note that I used __in_list as the member as we already >> > have a macro '#define EINA_INLIST Eina_Inlist __in_list', but a member >> > argument could be added just as well) >> > >> > Thoughts ? >> >> As we discussed on IRC, I like this. It would help avoid casts and try >> to make code bit easier to get right. > > much uglier as now you need to drag an offset # around all the time, and now > you still need to cast anyway (use a raw pointer offset and cast to ah Inlist > pointer). you don't get rid of it. > > inheritance in c in the end requires casting. thats how c does it. dont be > afraid of casting or think its ugly. it's how c becomes powerful and flexible.
As the macro says, it still does the cast, BUT this cast will add some safety since if you change types somewhere and forget in some place, compiler will warn you. The only problem I see and I already talked to Albin about it is on weird compilers without offsetof() macros. -- Gustavo Sverzut Barbieri http://profusion.mobi embedded systems -------------------------------------- MSN: barbi...@gmail.com Skype: gsbarbieri Mobile: +55 (19) 9225-2202 ------------------------------------------------------------------------------ Register Now & Save for Velocity, the Web Performance & Operations Conference from O'Reilly Media. Velocity features a full day of expert-led, hands-on workshops and two days of sessions from industry leaders in dedicated Performance & Operations tracks. Use code vel09scf and Save an extra 15% before 5/3. http://p.sf.net/sfu/velocityconf _______________________________________________ enlightenment-devel mailing list enlightenment-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/enlightenment-devel
