On Fri, 1 May 2009, Gustavo Sverzut Barbieri wrote:
> 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. offsetof seems to exist in the lib c of Microsoft Vincent ------------------------------------------------------------------------------ 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
