Re: [PATCH v2] <sys/param.h>: Add nitems() and snitems() macros

[Jonathan Wakely]

On 25/09/20 18:30 +0200, Alejandro Colomar via Libstdc++ wrote:
> Hello Jonathan,
>
> On 2020-09-25 16:48, Jonathan Wakely wrote:
> > Do you really need to provide snitems?
> >
> > Users can use (ptrdiff_t)nitems if needed, can't they?
>
> They can, but that adds casts in the code,
> which makes longer lines that are somewhat harder to read.
> To avoid that, users may sometimes omit the cast with possible UB.
> BTW, I use
>
> IMO, array indices should be declared as 'ptrdiff_t' always,
> and not 'size_t'.  More generically, I use unsigned integer types for two
> reasons:  bitwise operations, and library functions that require me to 
> do so.
>
> I don't intend to force anyone with my opinion, of course,
> but if I were to choose a type for 'nitems()', it would be 'ptrdiff_t'.
>
> However, for legacy reasons people will expect that macro to be unsigned,
> so I'd have 'nitems()' unsigned, and then a signed version prefixed 
> with an 's'.
>
> Some very interesting links about this topic:
>
> Bjarne Stroustrup (and others) about signed and unsigned integers:
> https://www.youtube.com/watch?v=Puio5dly9N8&t=12m56s
> https://www.youtube.com/watch?v=Puio5dly9N8&t=42m41s
>
> The two links above are two interesting moments of the same video.
>
> I guess that might be the reason they added std::ssize, BTW.

Yes, I'm aware of all the rationale. I already said that it makes
sense in C++ where you have generic code. I am not convinced that it's
necessary to add to <sys/param.h> when all it does is a cast from
size_t to ptrdiff_t.