<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Feb 10, 2019, at 17:11, Eric Fiselier via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="">Libc++ is a C++11 STL implementation that tolerates C++03 compilers.</div><div class="">If a feature can be reasonably implemented in C++03, then we provide it.</div></div></div></blockquote><div><br class=""></div><div>It can be implemented in C++03, however there will be a visible code complexity cost in doing so with Olivier's patch (mostly because of the lack of lambdas).</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><atomic> is one example, <thread>, <unordered_map> and `std::shared_ptr` are others.</div></div></div></blockquote><div><br class=""></div><div>Yes, but this was decided in a time where not many compilers supported C++11 properly, right? 8 years later, we have many compilers supporting C++11 properly.</div><div><br class=""></div><div>I suspect the number of people that use a recent libc++ with a compiler that does not support C++11 is very, very close to 0. One would have to deliberately update libc++ while keeping the compiler old, and then point the compiler to the updated libc++ headers manually. Additionally, the number of people that are in that setup AND that want to use std::atomic is likely to be even smaller.</div><div><br class=""></div><div>I have an impression that we might be making our lives harder just to provide something that nobody cares about. Is there a common use-case of libc++ I'm missing here? Maybe some Linux distribution doing something funky that makes the old-compiler-with-new-libc++ more widely used than I imagine?</div><div><br class=""></div><div>Unless we have a reason to do otherwise, I'd vote for not caring about C++03 support in <atomic>.</div><div><br class=""></div><div>Louis</div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Feb 6, 2019 at 11:39 PM Olivier Giroux via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div class="gmail-m_-2222480216075481894WordSection1"><p class="MsoNormal">Maybe another way to test these waters is to ask what is actually being _<i class="">tested_</i>?<u class=""></u><u class=""></u></p><p class="MsoNormal"><u class=""></u> <u class=""></u></p><p class="MsoNormal">Olivier<u class=""></u><u class=""></u></p><p class="MsoNormal"><u class=""></u> <u class=""></u></p>
<div style="border-right:none;border-bottom:none;border-left:none;border-top:1pt solid rgb(181,196,223);padding:3pt 0in 0in" class=""><p class="MsoNormal"><b class=""><span style="font-size: 12pt;" class="">From: </span></b><span style="font-size: 12pt;" class=""><<a href="mailto:jfbastien@apple.com" target="_blank" class="">jfbastien@apple.com</a>> on behalf of JF Bastien <<a href="mailto:jfbastien@apple.com" target="_blank" class="">jfbastien@apple.com</a>><br class="">
<b class="">Date: </b>Wednesday, February 6, 2019 at 11:21 AM<br class="">
<b class="">To: </b>Olivier Giroux <<a href="mailto:OGiroux@nvidia.com" target="_blank" class="">OGiroux@nvidia.com</a>><br class="">
<b class="">Cc: </b>"<a href="mailto:libcxx-dev@lists.llvm.org" target="_blank" class="">libcxx-dev@lists.llvm.org</a>" <<a href="mailto:libcxx-dev@lists.llvm.org" target="_blank" class="">libcxx-dev@lists.llvm.org</a>><br class="">
<b class="">Subject: </b>Re: [libcxx-dev] What C++03 support should <atomic> have?<u class=""></u><u class=""></u></span></p>
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</div><p class="MsoNormal">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.
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<div class=""><p class="MsoNormal">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?
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<div class=""><p class="MsoNormal">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?<u class=""></u><u class=""></u></p>
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<div class=""><p class="MsoNormal">On Feb 5, 2019, at 9:33 PM, Olivier Giroux via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" target="_blank" class="">libcxx-dev@lists.llvm.org</a>> wrote:<u class=""></u><u class=""></u></p>
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<div class=""><p class="MsoNormal">Sorry, that quote is from my patch, but there’s identical code elsewhere in the file. I swear!<span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"> <span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal">Olivier<span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"><b class=""><span style="font-size:12pt" class="">From:<span class="gmail-m_-2222480216075481894apple-converted-space"> </span></span></b><span style="font-size:12pt" class="">libcxx-dev <<a href="mailto:libcxx-dev-bounces@lists.llvm.org" target="_blank" class="">libcxx-dev-bounces@lists.llvm.org</a>> on behalf
of Olivier Giroux via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" target="_blank" class="">libcxx-dev@lists.llvm.org</a>><br class="">
<b class="">Reply-To:<span class="gmail-m_-2222480216075481894apple-converted-space"> </span></b>Olivier Giroux <<a href="mailto:OGiroux@nvidia.com" target="_blank" class="">OGiroux@nvidia.com</a>><br class="">
<b class="">Date:<span class="gmail-m_-2222480216075481894apple-converted-space"> </span></b>Tuesday, February 5, 2019 at 9:33 PM<br class="">
<b class="">To:<span class="gmail-m_-2222480216075481894apple-converted-space"> </span></b>"<a href="mailto:libcxx-dev@lists.llvm.org" target="_blank" class="">libcxx-dev@lists.llvm.org</a>" <<a href="mailto:libcxx-dev@lists.llvm.org" target="_blank" class="">libcxx-dev@lists.llvm.org</a>><br class="">
<b class="">Subject:<span class="gmail-m_-2222480216075481894apple-converted-space"> </span></b>[libcxx-dev] What C++03 support should <atomic> have?<u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal">There is a little bit of code in this file that suggests it once worked in C++03.<span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal">Like so:<span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal" style="line-height:13.5pt;background:rgb(30,30,30)"><span style="font-size:10pt;font-family:Consolas;color:rgb(197,134,192)" class="">#ifndef</span><span class="gmail-m_-2222480216075481894apple-converted-space"><span style="font-size:10pt;font-family:Consolas;color:rgb(86,156,214)" class=""> </span></span><span style="font-size:10pt;font-family:Consolas;color:rgb(220,220,170)" class="">_LIBCPP_CXX03_LANG</span><span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal" style="line-height:13.5pt;background:rgb(30,30,30)"><span style="font-size:10pt;font-family:Consolas;color:rgb(212,212,212)" class=""> <span class="gmail-m_-2222480216075481894apple-converted-space"> </span></span><span style="font-size:10pt;font-family:Consolas;color:rgb(220,220,170)" class="">__cxx_atomic_type</span><span style="font-size:10pt;font-family:Consolas;color:rgb(212,212,212)" class="">()
_NOEXCEPT =<span class="gmail-m_-2222480216075481894apple-converted-space"> </span></span><span style="font-size:10pt;font-family:Consolas;color:rgb(197,134,192)" class="">default</span><span style="font-size:10pt;font-family:Consolas;color:rgb(212,212,212)" class="">;</span><span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal" style="line-height:13.5pt;background:rgb(30,30,30)"><span style="font-size:10pt;font-family:Consolas;color:rgb(197,134,192)" class="">#else</span><span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal" style="line-height:13.5pt;background:rgb(30,30,30)"><span style="font-size:10pt;font-family:Consolas;color:rgb(212,212,212)" class=""> <span class="gmail-m_-2222480216075481894apple-converted-space"> </span></span><span style="font-size:10pt;font-family:Consolas;color:rgb(220,220,170)" class="">__cxx_atomic_type</span><span style="font-size:10pt;font-family:Consolas;color:rgb(212,212,212)" class="">()
_NOEXCEPT :<span class="gmail-m_-2222480216075481894apple-converted-space"> </span></span><span style="font-size:10pt;font-family:Consolas;color:rgb(220,220,170)" class="">__a_value</span><span style="font-size:10pt;font-family:Consolas;color:rgb(212,212,212)" class="">() {}</span><span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal" style="line-height:13.5pt;background:rgb(30,30,30)"><span style="font-size:10pt;font-family:Consolas;color:rgb(197,134,192)" class="">#endif</span><span class="gmail-m_-2222480216075481894apple-converted-space"><span style="font-size:10pt;font-family:Consolas;color:rgb(212,212,212)" class=""> </span></span><span style="font-size:10pt;font-family:Consolas;color:rgb(106,153,85)" class="">//
_LIBCPP_CXX03_LANG</span><span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal">Is that an actual design goal? It looks like it’s broken right now.<span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal">Do we maintain this, or do we bump the assumed default to C++11?<span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal">Thanks for your guidance,<span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal">Olivier<span style="font-size:12pt" class=""><u class=""></u><u class=""></u></span></p>
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