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.
--
Cheers,
David / dhildenb
