Re: [Qemu-devel] Stick to loops

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 12/10/2015 12:00, Daniel P. Berrange wrote:
>> 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.
>> 
>> > Higher-order functions are a wonderful tool if the language is equipped
>> > for them.  In Lisp, for instance, you'd have everything in one place and
>> > no need for the awkward marshalling and unmarshalling of arguments,
>> > thanks to nested functions.
>> > 
>> > In C, stick to loops.  That's what the language supports.
>> 
>> You're really arguing against use of function callbacks in general with
>> this comparison to LISP. I don't think that's really practical in the
>> real world, as any integration with event loop needs callbacks, which
>> share al the same limitations as callbacks used with this foreach()
>> style iterator. Given this I don't think banning use of callbacks in
>> one specific scenario is really beneficial in general - its really
>> just a personal style choice.

You're right, I do think callbacks in C are relatively awkward.  But
then you're attacking a strawman --- I did not advocate *banning*
callbacks.  That would be silly indeed.  I did advocate for using them
*sparingly*.

There are cases where callbacks are simply required, and you quoted one.

There are cases where callbacks compete with other techniques, and I
quoted one.

> I agree with Eric that in general loops are better than callbacks.

Me.  Eric's innocent :)

> However, there are cases where iterators are just as awkward to write.
> Considering that we have very few iterations on properties, I think your
> patches are fine.

Mind, I didn't actually object to them.  I merely voiced my reasoned
opinion on idiomatic iteration in C: stick to loops.

Just to deter strawmen: that's a rule of thumb, not a law :)