: add arithmetic overloads for std::lerp

[Igor Zhukov (fsb4000)]

Fixes #2112

Should I add remove_volatile or remove_cv for if constexpr conditions?

I think "No" but I am unsure.

[nicole mazzuca (strega-nil-ms)]

Not clear that this should be implemented

m

[Casey Carter (CaseyCarter)]

We can remove this again if LWG-3223 gains traction, but for now we're just creating a portability landmine by diverging from libc++ and libstdc++ (https://godbolt.org/z/TrPs9zae5). I'm happy to implement this if we cleanup the comment on 1312.

[Casey Carter (CaseyCarter)]

Should I add remove_volatile or remove_cv for if constexpr conditions?

I think "No" but I am unsure.

Not necessary. Top-level cv-qualifiers are stripped away by template argument deduction.

[Igor Zhukov (fsb4000)]

Not necessary. Top-level cv-qualifiers are stripped away by template argument deduction.

Yes, but a person could do a stupid thing like an explicit template instantiation, should we care about it?

https://gcc.godbolt.org/z/o89jraYbM

[Casey Carter (CaseyCarter)]

Yes, but a person could do a stupid thing like an explicit template instantiation, should we care about it?

https://gcc.godbolt.org/z/o89jraYbM

The Standard doesn't necessarily even say there's a template here, let alone what the template parameters are and what they mean. This is "play stupid games, win stupid prizes"-level undefined behavior.

[Stephan T. Lavavej (StephanTLavavej)]

⚠️ Note to self:

I must export this new overload of lerp().

[Stephan T. Lavavej (StephanTLavavej)]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[Stephan T. Lavavej (StephanTLavavej)]

Thanks for fixing this bug and improving portability! 🐞 ✅ 😸