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

JF Bastien via libcxx-dev libcxx-dev at lists.llvm.org
Wed Feb 6 11:20:56 PST 2019

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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