On 06.08.23 12:19, Jason Merrill wrote:
On Wed, Aug 2, 2023 at 12:02 PM Nikolas Klauser
<nikolasklau...@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?
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
Thanks for the answers!
There are a few really interesting extensions that I would like to use:
- inline variables
- variable templates
- `if constexpr`
- fold expressions
- conditional explicit
- static operator()
(https://godbolt.org/z/5n9Y4h69n)
Is anybody aware of any problems with these extensions? I'd be happy to
provide a patch to add these extensions to the documentation, but I
couldn't figure out how to build the documentation without building all
of gcc.
Nikolas
