From: Jonathan Wakely <jwakely@redhat.com>
To: Alejandro Colomar <colomar.6.4.3@gmail.com>
Cc: fweimer@redhat.com, linux-man@vger.kernel.org,
libc-alpha@sourceware.org, gcc@gcc.gnu.org,
rusty@rustcorp.com.au, linux-kernel@vger.kernel.org,
libstdc++@gcc.gnu.org, libc-coord@lists.openwall.com,
enh@google.com
Subject: Re: [PATCH v2] <sys/param.h>: Add nitems() and snitems() macros
Date: Fri, 25 Sep 2020 18:39:52 +0100 [thread overview]
Message-ID: <20200925173952.GN6061@redhat.com> (raw)
In-Reply-To: <22c110fe-4c92-e5e6-dc35-dbf00a97cfa2@gmail.com>
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.
next prev parent reply other threads:[~2020-09-25 17:40 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-20 23:00 Expose 'array_length()' macro in <sys/cdefs.h> or <sys/param.h> Alejandro Colomar
2020-09-21 8:38 ` Florian Weimer
2020-09-21 10:11 ` Alejandro Colomar
2020-09-21 10:33 ` Florian Weimer
2020-09-21 12:47 ` Alejandro Colomar
2020-09-21 15:47 ` [libc-coord] " enh
2020-09-22 16:25 ` Rich Felker
2020-09-22 16:44 ` Jonathan Wakely
2020-09-22 16:53 ` Ville Voutilainen
2020-09-21 14:01 ` Jonathan Wakely
2020-09-21 21:52 ` Expose 'array_length()' macro in <sys/param.h> Alejandro Colomar
2020-09-21 22:04 ` Jonathan Wakely
2020-09-21 22:13 ` Ville Voutilainen
2020-09-22 9:10 ` Alejandro Colomar
2020-09-22 9:40 ` Jonathan Wakely
2020-09-22 10:01 ` Florian Weimer
2020-09-22 10:35 ` Alejandro Colomar
2020-09-22 11:40 ` Florian Weimer
2020-09-22 14:58 ` [RFC] <sys/param.h>: Add nitems() and snitems() macros Alejandro Colomar
2020-09-25 13:20 ` [PATCH v2] " Alejandro Colomar
2020-09-25 14:10 ` Alejandro Colomar
2020-09-25 14:48 ` Jonathan Wakely
2020-09-25 16:30 ` Alejandro Colomar
2020-09-25 17:39 ` Jonathan Wakely [this message]
2020-09-25 17:42 ` Jonathan Wakely
2020-09-25 17:46 ` Alejandro Colomar
2020-09-25 19:37 ` [PATCH v3] <sys/param.h>: Add nitems() Alejandro Colomar
2020-09-22 9:16 ` [libc-coord] Re: Expose 'array_length()' macro in <sys/param.h> Florian Weimer
2020-09-30 15:58 ` Expose 'array_length()' macro in <sys/cdefs.h> or <sys/param.h> Joseph Myers
2020-09-30 20:39 ` Alejandro Colomar
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