From: Jonathan Wakely <jwakely@redhat.com>
To: Jason Merrill <jason@redhat.com>
Cc: Martin Sebor <msebor@gmail.com>,
Richard Biener <richard.guenther@gmail.com>,
gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PING][PATCH] define auto_vec copy ctor and assignment (PR 90904)
Date: Wed, 14 Jul 2021 11:47:24 +0100 [thread overview]
Message-ID: <CACb0b4m6BKh7SqQ+JOYigE3=PzNrNrdhPLL6A8p3tSsOVRRUTw@mail.gmail.com> (raw)
In-Reply-To: <2c60a7d0-3f60-b72f-c0f2-6fc7a4900740@redhat.com>
On Wed, 14 Jul 2021 at 04:39, Jason Merrill <jason@redhat.com> wrote:
>
> On 7/13/21 4:02 PM, Martin Sebor wrote:
> > On 7/13/21 12:37 PM, Jason Merrill wrote:
> >> On 7/13/21 10:08 AM, Jonathan Wakely wrote:
> >>> On Mon, 12 Jul 2021 at 12:02, Richard Biener wrote:
> >>>> Somebody with more C++ knowledge than me needs to approve the
> >>>> vec.h changes - I don't feel competent to assess all effects of the
> >>>> change.
> >>>
> >>> They look OK to me except for:
> >>>
> >>> -extern vnull vNULL;
> >>> +static constexpr vnull vNULL{ };
> >>>
> >>> Making vNULL have static linkage can make it an ODR violation to use
> >>> vNULL in templates and inline functions, because different
> >>> instantiations will refer to a different "vNULL" in each translation
> >>> unit.
> >>
> >> The ODR says this is OK because it's a literal constant with the same
> >> value (6.2/12.2.1).
> >>
> >> But it would be better without the explicit 'static'; then in C++17
> >> it's implicitly inline instead of static.
> >
> > I'll remove the static.
> >
> >>
> >> But then, do we really want to keep vNULL at all? It's a weird
> >> blurring of the object/pointer boundary that is also dependent on vec
> >> being a thin wrapper around a pointer. In almost all cases it can be
> >> replaced with {}; one exception is == comparison, where it seems to be
> >> testing that the embedded pointer is null, which is a weird thing to
> >> want to test.
> >
> > The one use case I know of for vNULL where I can't think of
> > an equally good substitute is in passing a vec as an argument by
> > value. The only way to do that that I can think of is to name
> > the full vec type (i.e., the specialization) which is more typing
> > and less generic than vNULL. I don't use vNULL myself so I wouldn't
> > miss this trick if it were to be removed but others might feel
> > differently.
>
> In C++11, it can be replaced by {} in that context as well.
Or if people don't like that, you could add a constructor taking
std::nullptr_t and an equality comparison with std::nullptr_t and then
use nullptr instead of vNULL.
I think just using {} for an empty, value-initialized vec makes more
sense though.
next prev parent reply other threads:[~2021-07-14 10:47 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-26 23:30 [PATCH] " Martin Sebor
2021-04-27 7:58 ` Richard Biener
2021-04-27 13:58 ` Martin Sebor
2021-04-27 14:04 ` Richard Biener
2021-04-27 15:52 ` Martin Sebor
2021-05-03 21:50 ` [PING][PATCH] " Martin Sebor
2021-05-11 20:02 ` [PING 2][PATCH] " Martin Sebor
2021-05-27 19:33 ` [PING 3][PATCH] " Martin Sebor
2021-05-27 20:53 ` [PATCH] " Jason Merrill
2021-06-01 19:56 ` Martin Sebor
2021-06-01 21:38 ` Jason Merrill
2021-06-25 20:51 ` Martin Sebor
2021-06-25 22:11 ` Jason Merrill
2021-06-25 22:36 ` Martin Sebor
2021-06-28 8:07 ` Richard Biener
2021-06-28 18:07 ` Martin Sebor
2021-06-29 10:58 ` Richard Biener
2021-06-29 11:34 ` Martin Jambor
2021-06-30 1:46 ` Martin Sebor
2021-06-30 8:48 ` Richard Biener
2021-06-30 9:29 ` Martin Jambor
2021-07-06 15:06 ` [PING][PATCH] " Martin Sebor
2021-07-07 7:28 ` Richard Biener
2021-07-07 14:37 ` Martin Sebor
2021-07-12 11:02 ` Richard Biener
2021-07-13 14:08 ` Jonathan Wakely
2021-07-13 18:37 ` Jason Merrill
2021-07-13 20:02 ` Martin Sebor
2021-07-14 3:39 ` Jason Merrill
2021-07-14 10:47 ` Jonathan Wakely [this message]
2021-07-14 14:46 ` Martin Sebor
2021-07-14 16:23 ` Jason Merrill
2021-07-20 18:34 ` Martin Sebor
2021-07-20 20:08 ` Jason Merrill
2021-07-20 21:52 ` Martin Sebor
2021-07-27 18:56 ` Martin Sebor
2021-07-30 15:06 ` Jason Merrill
2021-08-06 2:07 ` Martin Sebor
2021-08-06 7:52 ` Christophe Lyon
2021-08-06 12:17 ` Christophe Lyon
2021-07-14 14:44 ` Martin Sebor
2021-06-29 14:43 ` [PATCH] " Jason Merrill
2021-06-29 17:18 ` Martin Sebor
2021-06-30 8:40 ` Richard Biener
2021-06-30 9:00 ` Richard Sandiford
2021-06-30 12:01 ` Richard Biener
2021-06-28 8:05 ` Richard Biener
2021-06-29 12:30 ` Trevor Saunders
2021-06-02 6:55 ` Richard Biener
2021-06-02 16:04 ` Martin Sebor
2021-06-03 8:29 ` Trevor Saunders
2021-06-07 8:51 ` Richard Biener
2021-06-07 10:33 ` Trevor Saunders
2021-06-07 13:33 ` Richard Biener
2021-06-07 20:34 ` Martin Sebor
2021-06-08 3:26 ` Trevor Saunders
2021-06-08 7:19 ` Richard Biener
2021-06-07 22:17 ` Martin Sebor
2021-06-08 2:41 ` Trevor Saunders
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