[Toybox] ?: proposal for ISO C

[enh]

On Tue, Jul 8, 2025 at 7:50 PM Rob Landley <rob at landley.net> wrote:
>
> On 7/8/25 15:44, Alejandro Colomar wrote:
> > [CC += wg14]
> >
> > Hi Elliott, Rob,
> >
> > On Tue, Jul 08, 2025 at 03:32:37PM -0400, enh wrote:
> >> On Tue, Jul 1, 2025 at 1:52 PM Rob Landley <rob at landley.net> wrote:
> >>> I spent many years figuring out what I could throw away. That quote from
> >>> the guy who wrote "The Little Prince" was my email sig for a while:
> >>>
> >>> https://www.goodreads.com/quotes/19905-perfection-is-achieved-not-when-there-is-nothing-more-to
> >
> > [...]
> >
> >>>>> it's been implemented by clang/gcc for a long time, but if you're
> >>>>> going to be a standards lawyer about it, __has_include() is c++17 and
> >>>>> c23.
> >>>
> >>> Sigh. Did one of the standards finally include gcc's empty ? : middle
> >>> argument? (Which I use all the time...)
> >>
> >> c23 does not include this, and i don't think i've seen a proposal to
> >> standardize it. +Alejandro Colomar pays more attention to wg14 though,
> >> so he might know better...
> >>
> >>> Sadly, standards remain a frame of reference to diverge from...
> >
> > I've written a proposal for standardization of that.  So far, I've only
> > presented it informally (via email) to the committee, but I'll turn it
> > into a proper paper after the next meeting that will be in August.
> >
> > Here's my draft proposal:
> > <https://www.alejandro-colomar.es/src/alx/alx/wg14/alx-0030.git/tree/alx-0030.txt>
> > (Anyway, I've pasted it at the bottom of the email, for convenience.)
> >
> > In August, we'll vote a proposal on which mine depends for the wording,
> > which is why I didn't yet present an N document.
> >
> > I've CCed the committee in this email, so that they see that people are
> > interested in having this feature and use it all the time.
> >
> > Feel free to comment on the proposal, if you think you'd add anything to
> > the rationale.
>
> Rationale? As in why I was surprised this wasn't in C11?

(fwiw, in terms of "is this used much?" there are a thousand different
_files_ in the Android source tree where ?: is used in c [i
deliberately didn't count c++, nor any matches in clang/llvm, where
it's hard to distinguish legit uses from implementation/tests]. since
most google-written source is c++, this means that over 950 of those
files are from third-party open source c projects we pull in.)

> The linux 1.0 kernel circa 1994 used the ? : operator 4 times in
> fs/pipe.c (which is not optional, that's a core file part of all builds
> no matter the target or configuration). This stayed the only uses for
> 1.2 and 2.0, but in 2.2 (1999) it expanded to 31 uses in multiple files.

(someone should fix the wikipedia page which only has "at least 2001"
for gcc :-) )

> When Intel extended its proprietary ICC to build Linux 2.4.21 (ala
> https://community.intel.com/legacyfs/online/drupal_files/article/146679/linuxkernelbuildwhitepaper.pdf)
> the ? : operator was one of the things they added support for (although
> the name "elvis operator" hadn't been coined yet,
> https://web.archive.org/web/20170830022856/https://software.intel.com/sites/default/files/m/d/4/1/d/8/Intel_Linux_Compiler_12_01_GNU_Compatibility_rev10.pdf
> called it "conditionals with omitted operands".)
>
> When tinycc built a 2.4.26 kernel ala
> https://bellard.org/tcc/tccboot.html back in 2004 it also had to support
> empty "? :".
>
> By the time Clang/LLVM built a Linux 2.6.36 in 2010
> (https://lwn.net/Articles/411654/) support for ? : was a well-known
> requirement for building Linux and linux programs like busybox (release
> 1.2.2 in 2006 had 9 instances).
>
> Even small compilers like libfirm/cparser support this (ala

yeah, chibicc too: https://github.com/rui314/chibicc/blob/main/parse.c#L2185

> https://github.com/libfirm/cparser/commit/315d496108eb from 2007) and I
> just built a quick test program with the current
> https://github.com/PortableCC/pcc to confirm that supports it too
> (although the git repository history only goes back to 2002, beginning
> with a single "import" commit flattening the earlier history, so if
> there was a specific commit mentioning ? : in its description it was
> before then.) I believe that's the compiler that FreeBSD switched to
> clang from?
>
> All of that predated C11. FreeBSD and MacOS support ? : just fine in a
> simple "cc hello.c" using the stock host $PATH, no homebrew required, no
> idea when they last _didn't_.
>
> IBM's big iron tech all started soaking up serious linux-isms in 2001
> with Gerstner's "billion dollars a year on linux" announcement, long
> before they were reverse-acquired by Red Hat, and I believe this was one
> of them all the way back then. The OS/2 development staff consolidated
> from Boca Raton to Austin in 1996 became the core of the IBM Linux
> Technology Center 5 years later, AIX 5L was also 2001, Linas Vepstas'
> "bigfoot" port of Linux to the 360 was 1998 ala
> https://linas.org/linux/i370-why.html ...
>
> As always, I have no idea what Windows is doing.
>
> Rob
>
> P.S. I don't know where the name "Elvis operator" came from. Page 11 of
> https://github.com/CppCon/CppCon2019/blob/master/Presentations/nonconforming_cpp/nonconforming_cpp__miro_knejp__cppcon_2019.pdf
> also calls it "conditionals with omitted operands", and 6 minutes into
> https://www.youtube.com/watch?v=IAdLwUXRUvg the guy giving that
> presentation calls it that and then boggles at the name "elvis
> operator". I think the email this is replying to is second time I've
> ever heard anyone call it that, and vaguely assumed it was some sort of
> pun on vi using colon commands a lot.

yeah, i don't hear it much amongst c programmers, but it's common to
call it that in _other_ languages.