Comment by snnn | Hacker News Reader

Comment by snnn | Hacker News Reader

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If everyone just use the latest macOS and the latest iOS, I'm less concerned. But I haven't heard any IT manager enforcing that. macOS 12 has come out, but usually they still allows you using macOS 11 as long as you have installed all the security bug fixes.

For macOS and iOS, the problem is more complicated. Let's say I want to publish a package to pypi.org. The package contains some binaries compiled from C++ and it requires C++17. Then what is the lowest macOS version the binary can support?? It's very tricky that if the build machine which generates the package is macOS 11, then it can have Xcode 12.5. Otherwise it has to use XCode 12.4 or lower. And in XCode 12.4 it says std::optional, which is a C++17 feature, is only supported in macOS 10.14+. But if the build machine has macOS 11 and XCode 12.5, then the binary would be able to run on 10.13 too. And in whatever case, it can't support 10.12 or lower.

I believe you don't want to build tensorflow/pytorch packages from source. So the maintainers of these two OSS projects must consider the things above. If you wonder why they don't use C++17, this is the reason. For the same reason they want to avoid C11 optional features too.

So you are conflating tons of things here and none of it really makes sense. The reason why compiling for macOS tends to claim stuff like how C++ features are tied to operating system targets is because Apple doesn't really understand how to do toolchain architecture well and so have managed to do this awkward thing where the operating system--from their perspective--is this massive monolithic brick that contains a ton of functionality that is classically introduced by the toolchain, which I admit has some advantages but generally feels ill-intentioned.

The result of this is that Apple really assumes you are going to use the copy of libc++ that ships on the system, and it might be missing exported systems that are assumed by the library. But this isn't related to the toolchain you are using. I do remember some weird corner case with std::optional and I think it might have been that Apple forgot to mark something correctly as unsupported in a previous toolchain build? The newer compiler is thereby actually giving you the more correct understanding of what can actually be presumed to work on older systems.

But like, the core issue here is that you really shouldn't use Apple's stupid toolchain setup, nor do you have to: just embed your own copy of libc++ and call it a day. I routinely use the latest versions of Xcode's copy of clang (though I prefer to compile for macOS now using the copy of clang that comes with the Android NDK for various reasons: I recommend avoiding Xcode except to get their system headers) to target ancient systems with modern C++ features as I'm not relying on the system copy of libc++ to even exist or work (10.7's doesn't) much less be complete.

> Then what is the lowest macOS version the binary can support??? It's very tricky [...]

No it's not. The oldest supported version of macOS your binary will run on will be the one you set in your CFLAGS with the -mmacosx-version-min=10.x flag when you build.

The OS you are running the build on and the Xcode version don't influence that, you should just run the most recent Xcode you can, build against the most recent macOS SDK available and set that flag. You can target 10.8 from Big Sur and Xcode 12 with afaik no issues.

> The OS you are running the build on and the Xcode version don't influence that

Usually it doesn't. But in this special case it does. I have set the flag you said. When C++17 wasn't in the picture, it's enough. But now we are talking about how to enable developer using the new language features. New C++ features typically need new runtime. But the old systems do have it. Then one of the difficulty is how to figure out which macOS versions have it, which doesn't.

The std::optional / std::variant case is unfortunate indeed, it's sadly an argument for using non-std versions of these types. It's also possible to cheat a bit with libc++ macros.. -D_LIBCPP_NO_EXCEPTIONS=1 does the trick (but turns exceptions into asserts).

You can also link statically against libc++.

Thanks for the info. Would there likely be a downside to saying "if you want to use the precompiled packages, you need to be on macOS 11+ (but feel free to DIY if you're stuck on an older version)"?

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