Re: [gil] Phasing out support C++11 and switching to C++17

From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2020-10-26 15:49:56

On Mon, 26 Oct 2020 at 16:16, Mike via Boost <boost_at_[hidden]> wrote:
> > Gesendet: Montag, 26. Oktober 2020 um 11:41 Uhr
> > Von: "Mateusz Loskot via Boost" <boost_at_[hidden]>
> > On Mon, 26 Oct 2020 at 11:17, Mike via Boost <boost_at_[hidden]> wrote:
> >
> > > E.g. I think the first c++17 bits have been implemented in
> > > gcc 6 and  gcc 7 had mostly complete support, but it took
> > > till gcc 9 before the standard library gained support for pmr
> > > and to_chars is - to the bestof my knowledge - still not
> > > implemented for floating point types even in g++-10/11.
> >
> > One of motivations is to drop support for GCC 5,
> > It just seem simpler to assume C++17 as requirement
> > with comment that some compilers w/ partial C++17
> > support may still work.
>
> The problem I see  is: If you are pedantic, then there
> isn't a complete c++17 toolchain on linux yet.

GIL will not require feature-complete C++17 compiler
We should be good with the last of the GCC 6 kind [1]
or we may require GCC 7. The specifics will be decided
as we go, as contributors will require.
The deal is to announce C++11 phasing out early/now,
to let ourselves time, at least two releases, but in
practices it will be longer before we bump required
compiler versions high.

> So unless
> you are saying, all current version of gcc/clang/libstdc++
> "may still work" but are not really supported, you need
> to be more specific in what you require and support.
> Where support means (to me) "Will be regularly tested and
> will continue to work for the next couple of releases/years".

Yes, we will aim to cover claimed support with CI and Boost
regression tests matrix.

> > It may also be possible to list required C++17 features
> > per Boost (GIL) release, but that list may change
> > in any next release, obviously.
>
> I wouldn't go there, because it isn't easy to actually verify
> that the documented features and the used features stay in sync

I made a mistake.
Above I meant to write "Boost (GIL) release notes",
where we can list GIL's required C++17 features for
particular Boost release, just for user's convenience
and change/remove that list from release notes in future.

[1] https://gcc.gnu.org/legacy-ml/gcc/2018-10/msg00113.html

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net