From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: Jason Merrill <jason@redhat.com>
Cc: Nikolas Klauser <nikolasklauser@berlin.de>,
gcc@gcc.gnu.org, Louis Dionne <ldionne.2@gmail.com>,
Mark de Wever <koraq@xs4all.nl>,
aaron@aaronballman.com, "libstdc++" <libstdc++@gcc.gnu.org>
Subject: Re: GCC support for extensions from later standards
Date: Sun, 6 Aug 2023 20:43:16 +0100 [thread overview]
Message-ID: <CAH6eHdSbCLE6VtdNF16TXynWf=bjNedjFxdSVCMkqgyp2M7PQw@mail.gmail.com> (raw)
In-Reply-To: <CADzB+2mGjdH6xDnJq+So4h2+56SQsNjFDmRVid9dCZ0evieE-g@mail.gmail.com>
On Sun, 6 Aug 2023 at 20:20, Jason Merrill via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> On Wed, Aug 2, 2023 at 12:02 PM Nikolas Klauser <nikolasklauser@berlin.de>
> wrote:
>
> > Hi everyone!
> >
> > I'm working on libc++ and we are currently discussing using language
> > extensions from later standards (
> > https://discourse.llvm.org/t/rfc-use-language-extensions-from-future-standards-in-libc/71898/4).
> > By that I mean things like using `if constexpr` with `-std=c++11`. GCC has
> > quite a lot of these kinds of conforming extensions, but doesn't document
> > them AFAICT. While discussing using these extensions, the question came up
> > what GCCs support policy for these is. Aaron was kind enough to answer
> > these questions for us on the Clang side. Since I couldn't find anything in
> > the documentation, I thought I'd ask here.
> >
> > So, here are my questions:
> >
> > Do you expect that these extensions will ever be removed for some reason?
> > If yes, what could those reasons be?
> >
>
> Potentially, if they don't actually work properly in earlier standard
> modes. I recently noticed that while we allow DMI and =default in C++03
> mode with a pedwarn, combining them doesn't work.
>
> Some of the extensions are needed by libstdc++ and are therefore well
> tested; these are extremely unlikely to ever be removed. libstdc++ folks,
> is there a list of these?
We use variadic templates and long long in C++98. We use a DMI in
__gnu_cxx::__mutex even in C++98. I don't think we unconditionally use
anything else, because we can't rely on it being available when using
non-GCC compilers, or when compiling with -Wsystem-headers -pedantic.
We don't use if-constexpr before C++17 for example.
>
> Would you be interested in documenting them?
> >
>
> That would be useful, yes.
>
> There is a patch in review to add __has_feature/__has_extension to G++,
> which would seem like a suitable context for this documentation.
>
> Aaron noted that we should ask the Clang folks before using them, so they
> > can evaluated whether the extension makes sense, since they might not be
> > aware of them, and some might be broken. So I'd be interested whether you
> > would also like us to ask whether you want to actually support these
> > extensions.
> >
>
> Sounds good.
>
> Jason
next prev parent reply other threads:[~2023-08-06 19:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-02 19:01 Nikolas Klauser
2023-08-06 19:19 ` Jason Merrill
2023-08-06 19:43 ` Jonathan Wakely [this message]
2023-08-07 13:04 ` Jonathan Wakely
2023-08-08 8:55 ` Jonathan Wakely
2023-08-08 3:03 ` Nikolas Klauser
2023-08-08 7:33 ` Jakub Jelinek
2023-08-08 16:03 ` Nikolas Klauser
2023-08-08 16:07 ` Jonathan Wakely
2023-08-08 16:10 ` Jonathan Wakely
2023-08-08 16:33 ` Nikolas Klauser
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAH6eHdSbCLE6VtdNF16TXynWf=bjNedjFxdSVCMkqgyp2M7PQw@mail.gmail.com' \
--to=jwakely.gcc@gmail.com \
--cc=aaron@aaronballman.com \
--cc=gcc@gcc.gnu.org \
--cc=jason@redhat.com \
--cc=koraq@xs4all.nl \
--cc=ldionne.2@gmail.com \
--cc=libstdc++@gcc.gnu.org \
--cc=nikolasklauser@berlin.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).