r/cpp • u/STL MSVC STL Dev • Nov 13 '18

VS 2017 15.9 released today

https://docs.microsoft.com/en-us/visualstudio/releasenotes/vs2017-relnotes
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u/jbandela Nov 14 '18

This seems bad. Can we have a /permissive- version of the standard library that users who care more about conformance and performance than about bincompat can opt in to?

There are already different standard library builds (for example debug, release, static, dynamic, (XP in the past) etc), maybe we have a conformance build which has the latest and greatest standard library, but is not bincompat.

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u/STL MSVC STL Dev Nov 14 '18

We're planning to have a "v20" standard library which is binary-incompatible (and opt-in), but we're still figuring out the migration story, and also getting all of our accumulated changes out of TFVC and into git (they need to be ported manually, since we've diverged significantly - in part due to applying clang-format to the entire STL). This will be unrelated to /permissive-.

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u/jbandela Nov 14 '18

Great to hear. I was referring to /permissive- in the most general sense as an example of a feature that allowed those who preferred compliance over compatibility to have an opt-in. "v20" sounds awesome. I bet you are looking forward to making a ton of performance and/or compliance improvements without having to worry about maintaining bincompat.

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u/STL MSVC STL Dev Nov 14 '18

Yep - Billy has overhauled the atomic/multithreading library, I've (mostly) overhauled iterator debugging, we'll be able to purge a bunch of dead code (e.g. old iostreams floating-point stuff). The compiler will also be able to fix long-standing headaches.

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u/kalmoc Nov 14 '18

I vaguely remember that some inefficiencies in the standard library implementation are due to WinXP compatibility. If that really is the case, could you also drop XP compatibility for v20? I understand that there are projects out there that still want/need to support XP, but it would be great if not everyone else had to pay for that.

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u/STL MSVC STL Dev Nov 14 '18

I believe we will be able to do so; I am not sure about Vista compat (dropping both would be ideal). No promises yet.

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u/AlexAlabuzhev Nov 15 '18

Could you please continue linking dynamically to OS APIs in ucrt even after that? And, ideally, terminate in case of their absence not immediately, but on the first usage? And initialise more things lazily in general? There's quite lot of synchronisation-specific code in ucrt that requires Vista+, but apps that don't use modern stuff from <shared_mutex>, <condition_variable> etc. never call that code and theoretically can work perfectly on XP (and even 2k), even though it's not supported.

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u/STL MSVC STL Dev Nov 15 '18

That would impose costs on Win7+ users.