[libcxx-dev] What C++03 support should <atomic> have?

[Eric Fiselier via libcxx-dev]

Libc++ is a C++11 STL implementation that tolerates C++03 compilers.
If a feature can be reasonably implemented in C++03, then we provide it.
<atomic> is one example, <thread>, <unordered_map> and `std::shared_ptr`
are others.

All of these components should have tests that run in C++03 (Tests are
disabled in C++03 using the comment // UNSUPPORTED: c++98, c++03).




On Wed, Feb 6, 2019 at 11:39 PM Olivier Giroux via libcxx-dev <
libcxx-dev at lists.llvm.org> wrote:

> Maybe another way to test these waters is to ask what is actually being _
> *tested_*?
>
>
>
> Olivier
>
>
>
> *From: *<jfbastien at apple.com> on behalf of JF Bastien <jfbastien at apple.com
> >
> *Date: *Wednesday, February 6, 2019 at 11:21 AM
> *To: *Olivier Giroux <OGiroux at nvidia.com>
> *Cc: *"libcxx-dev at lists.llvm.org" <libcxx-dev at lists.llvm.org>
> *Subject: *Re: [libcxx-dev] What C++03 support should <atomic> have?
>
>
>
> Doing atomics before 11 was pretty wild… So I understand that people using
> an old C++ want some nice atomics. At the same time… They really should
> update to C++11 or later.
>
>
>
> What does libc++ try to do with new library features on old languages?
> Seems easy enough so support most of say optional or variant (without CTAD)
> before C++17. Is this done consistently? And how far back, do we even try
> to support C++98?
>
>
>
> It seems like we can be nice where it’s easy, but at some point in time
> are we just supporting stuff nobody cares about?
>
>
>
>
>
> On Feb 5, 2019, at 9:33 PM, Olivier Giroux via libcxx-dev <
> libcxx-dev at lists.llvm.org> wrote:
>
>
>
> Sorry, that quote is from my patch, but there’s identical code elsewhere
> in the file. I swear!
>
>
>
> Olivier
>
>
>
> *From: *libcxx-dev <libcxx-dev-bounces at lists.llvm.org> on behalf of
> Olivier Giroux via libcxx-dev <libcxx-dev at lists.llvm.org>
> *Reply-To: *Olivier Giroux <OGiroux at nvidia.com>
> *Date: *Tuesday, February 5, 2019 at 9:33 PM
> *To: *"libcxx-dev at lists.llvm.org" <libcxx-dev at lists.llvm.org>
> *Subject: *[libcxx-dev] What C++03 support should <atomic> have?
>
>
>
> There is a little bit of code in this file that suggests it once worked in
> C++03.
>
>
>
> Like so:
>
> #ifndef _LIBCPP_CXX03_LANG
>
>     __cxx_atomic_type() _NOEXCEPT = default;
>
> #else
>
>     __cxx_atomic_type() _NOEXCEPT : __a_value() {}
>
> #endif // _LIBCPP_CXX03_LANG
>
>
>
> Is that an actual design goal? It looks like it’s broken right now.
>
>
>
> Do we maintain this, or do we bump the assumed default to C++11?
>
>
>
> Thanks for your guidance,
>
>
>
> Olivier
>
>
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