[Toybox] ({}) proposal for ISO C

[Rob Landley]

On 7/12/25 07:20, Alejandro Colomar wrote:
> Hi Rob, Elliott,
> 
> The C Committee is discussing standardization of ({}).
> 
> <https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html>

Huh, gcc can do lambdas? Didn't know that...

> It would be interesting to know which implementations support this.  And
> also how widely used this is in random code.  If you can search in
> Android code, and all the weird implementations you know, it would be
> interesting information to present to the committee.  Thanks!!

Never heard of it.

I've used "do {blah;} while(0);" on several occasions so you can have an 
if (blah) thingy(); else thingy(); where thingy is a macro and the 
levels work out right without curly brackets, but this I don't recognize...

Hmmm, apparently the maxof() and minof() macros in toybox's lib/lib.h 
are using that. In 2017 I peeled max() and min() out of the xz code 
because it was doing it wrong, and I looked up an implementation that 
DIDN'T evaluate the arguments multiple times, because I'd seen it before 
(int the kernel among other places) and knew that was possible.

The kernel's been doing the variant I used since 2002:

https://lwn.net/Articles/983965/

https://github.com/mpe/linux-fullhistory/commit/ebe8851e282e3

Note that the fullhist tree goes back to 0.0.1 including the old 
bitcreeper commits and the patches for each dot release before that. 
Linus's current tree starts suddenly in 2012 so it's terrible for 
figuring out WHY things happened, it just starts a priori ex cathedra.

Before that they used "type _x = (x);" instead of typeof(), which... I 
have no idea. But "curly brackets in parentheses" is apparently a thing 
Linux's kernel.h has been using for min() and max() since... (git 
annotate file, git show $HASH, git checkout $HASH^1, git annotate file...)

$ git show 1012854f47d66
Author: linus1 <torvalds at athlon.transmeta.com>
Date:   Thu Aug 16 11:00:00 2001 -0600

     v2.4.8.4 -> v2.4.9
...
       - David Miller: "min()/max()" cleanups. Understands signs and sizes.
...
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -112,6 +112,11 @@ static inline void console_verbose(void)
         ((unsigned char *)&addr)[1], \
         ((unsigned char *)&addr)[0]

+#define min(type,x,y) \
+       ({ type __x = (x), __y = (y); __x < __y ? __x: __y; })
+#define max(type,x,y) \
+       ({ type __x = (x), __y = (y); __x > __y ? __x: __y; })
+

That commit did a big "we have a zillion redundant definitions of 
min/max and they're all wrong, let's collate them into one and use it" 
cleanup. No seriously, it removed 43 redundant definitions:

   $ git show 1012854f47d66 | grep '^-#define min' | wc -l
   43

I have no strong opinion on this construct, but it's another thing the 
kernel's been using for a quarter century, which Intel had to add to 
brag that ICC could build Linux, and Tinycc for tccboot in 2004, then 
llvm...

Rob