David Hildenbrand <david@xxxxxxxxxx> writes: > On 11.10.24 13:19, Andy Shevchenko wrote: >> On Fri, Oct 11, 2024 at 02:15:55PM +0300, Andy Shevchenko wrote: >>> 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. >> For any context as Ying provided an example with calls, they have to >> be >> idempotent, or you definitely get two different pointers for these, which is >> bigger issue that what I described above. > > Ah, now I understood what Ying meant: if the root pointer is modified > within the loop body we'd be in trouble. Given we cannot provide a good macro implementation to traverse only the descendant tree of _root, I suggest to just keep current for_each_resource() implementation. There is only one user of the proposed new macro to traverse the descendant tree. So, I suggest to open coded the for loop instead. More comments can be added to make it clear. -- Best Regards, Huang, Ying
