On Fri, Oct 11, 2024 at 12:51:09PM +0200, David Hildenbrand wrote: > On 11.10.24 12:49, Andy Shevchenko wrote: > > On Fri, Oct 11, 2024 at 09:06:37AM +0800, Huang, Ying wrote: > > > David Hildenbrand <david@xxxxxxxxxx> writes: > > > > On 10.10.24 08:55, Huang Ying wrote: ... > > > > for ((_p) = (_root)->child; (_p); (_p) = next_resource_XXX(_root, _p)) > > > > > > Yes. This can improve code readability. > > > > > > A possible issue is that "_root" will be evaluated twice in above macro > > > definition. IMO, this should be avoided. > > > > Ideally, yes. But how many for_each type of macros you see that really try hard > > to achieve that? I believe we shouldn't worry right now about this and rely on > > the fact that root is the given variable. Or do you have an example of what you > > suggested in the other reply, i.e. where it's an evaluation of the heavy call? > > > > > Do you have some idea about > > > how to do that? Something like below? > > > > > > #define for_each_resource_XXX(_root, _p) \ > > > for (typeof(_root) __root = (_root), __p = (_p) = (__root)->child; \ > > > __p && (_p); (_p) = next_resource_XXX(__root, _p)) > > > > This is a bit ugly :-( I would avoid ugliness as long as we have no problem to > > solve (see above). > > Fully agreed, I didn't quite understand the concern about "evaluation" at > first. It's a basic concept for macros and a good mine field even for the simple cases. > If it's just reading a variable twice, it doesn't matter at all right > now. The problem (even if it's a variable) is that the content of variable can be changed when run in non-atomic context, i.e. two evaluations will give two different results. Most "simple" for_each macros leave this exercise to the caller. That's what I also suggest for now. -- With Best Regards, Andy Shevchenko
