Hi
Am 8. August 2024 10:26:14 MESZ schrieb Alejandro Colomar <a...@kernel.org>:
> Hello Jens,
>
> On Thu, Aug 08, 2024 at 07:35:12AM GMT, Jₑₙₛ Gustedt wrote:
> > Hello Alejandro,
> >
> > On Thu, 8 Aug 2024 00:44:02 +0200, Alejandro Colomar wrote:
> >
> > > +Its syntax is similar to @code{sizeof}.
> >
> > For my curiosity, do you also make the same distinction that with
> > expressions you may omit the parenthesis?
>
> I thought of it. TBH, I haven't tested that thoroughly.
>
> In principle, I have implemented it in the same way as sizeof, yes.
>
> Personally, I would have never allowed sizeof without parentheses, but I
> understand there are people who think the parentheses hurt readability,
> so I kept it in the same way.
>
> I'm not sure why the parentheses are necessary with type names in
> sizeof,
probably because of operator precedence. there would be no rule that tells us
where sizeof ends and we'd switch back from parsing a type to parsing an
expression
> but to maintain expectations, I think it would be better to do
> the same here.
Just to compare, the recent additions in C23 typeof etc. only have the
parenthesized versions. So there would be precedent. And it really eases
transition
> >
> > I wouldn't be sure that we should continue that distinction from
> > `sizeof`.
>
> But then, what do we do? Allow lengthof with type names without parens?
> Or require parens? I'm not comfortable with that choice.
>
> > Also that prefix variant would be difficult to wrap in a
> > `lengthof` macro (without underscores) as we would probably like to
> > have it in the end.
>
> Do you mean that I should add _Lengthof? We're adding __lengthof__ to
> be a GNU extension with relative freedom from ISO. If I sent a patch
> adding _Lengthof, we'd have to send a proposal to ISO at the same time,
> and we'd be waiting for ISO to discuss it before I can merge it. And we
> couldn't bring prior art to ISO.
>
> With this approach instead, the plan is:
>
> - Merge __lengthof__ in GCC before ISO hears of it (well, there are
> already several WG14 members in this discussion, so you have actually
> heard of it, but we're free to do more or less what we want).
>
> - Propose _Lengthof to ISO C, with prior art in GCC as __lengthof__,
> proposing the same semantics. Also propose a lengthof macro defined
> in <stdlength.h>
I don't really see why we should take a detour via _Lengthof, I would hope we
could directly propose lengthof as the standardization
> - When ISO C accepts _Lengthof and lengthof, map _Lengthof in GCC to
> the same internals as __lengthof__, so they are the same thing.
>
> Still, I'm interested in having some feedback from WG14, to prevent
> implementing something that will have modifications when merged to
> ISO C, so please CC anyone interested from WG14, if you know of any.
I think that more important would be to have clang on board with this.
In any case, thanks for doing this!
Jens
--
Jens Gustedt - INRIA & ICube, Strasbourg, France
