Re: [Qemu-devel] Stick to loops (was: [PATCH v3 1/5] qom: introduce object_property_foreach method)

[Daniel P. Berrange]

On Mon, Oct 12, 2015 at 11:00:04AM +0100, Daniel P. Berrange wrote:
> On Fri, Oct 09, 2015 at 10:31:26AM +0200, Markus Armbruster wrote:
> > We have quite a few _foreach-functions to help iterate over various
> > things.  They are easy enough to write, but I find them awkward to use.
> > 
> > Implementing bdrv_next() is no harder than bdrv_iterate().  Compare:
> > 
> >     BlockDriverState *bdrv_next(BlockDriverState *bs)
> >     {
> >         if (!bs) {
> >             return QTAILQ_FIRST(&bdrv_states);
> >         }
> >         return QTAILQ_NEXT(bs, device_list);
> >     }
> > 
> >     void bdrv_iterate(void (*it)(void *opaque, BlockDriverState *bs), void 
> > *opaque)
> >     {
> >         BlockDriverState *bs;
> > 
> >         QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
> >             it(opaque, bs);
> >         }
> >     }
> 
> I don't think your example here is a reasonable comparison when you consider
> the full extent of this patch series. You are only having to iterate over a
> single data structure here. At the end of this patch series we have to
> iterate over multiple data structures spread across the object instance
> and class hierarchy, so writing a 'next' like method is not as trivial
> as you suggest with this comparison.

So it turns out I was wrong here. After a little more thinking I found
it was in fact fairly trivial to support a "next" like iterator in this
QOM property scenario, even when taking class properties into account.
So I'll re-spin this patch series with that approach, since it makes
the diffs much smaller

Regards,
Daniel
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