Re: [PATCH v2] _Generic.3: New page documenting _Generic()

[Alejandro Colomar <alx.manpages@gmail.com>]

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Hi Florian,

On 8/23/22 09:58, Florian Weimer wrote:

> Note that this approach does not really work that well in practice
> because macros using _Generic expand all the alternatives (in current
> implementations; doing this differently requires deviating from the
> layered implementation strategy suggested in the C standard).  This
> means that _Generic-using macros can only be nested maybe three or four
> levels deep, depending on the number of _Generic alternatives on each
> level.  For <tgmath.h>, this is really not enough, so a high-quality
> implementation of <tgmath.h> using _Generic is not feasible.  GCC
> provides __builtin_tgmath, which is designed in such a way that when
> used in a macro, the macro argument is only expanded once.
> 
> Maybe mention this under BUGS?
> 
> C++ templates do not suffer from this particular problem.


Ahh, I get it now.  You mean that the preprocessed code could grow 
exponentially, even if the assembly code is safe from such bloat, right?

Yeah, probably that should go into CAVEATS.

Would you mind sending a patch?

Anyway, if the standard defined intmax_t as a macro, it should probably 
not specify how that macro is implemented; this is just a simple 
suggestion, but a builtin of course would be better.

Cheers,

Alex

-- 
Alejandro Colomar
<http://www.alejandro-colomar.es/>

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