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Re: [SG10] Missing feature test macros for C++20 core papers

From: Casey Carter <cartec69_at_[hidden]>
Date: Fri, 15 Oct 2021 15:42:16 -0700
On Fri, Oct 15, 2021 at 3:27 PM Jonathan Wakely via SG10 <
sg10_at_[hidden]> wrote:

> I think the following papers should have had a feature test macro:
> P0848
> <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0848r3.html>
> Conditionally Trivial Special Member Functions
> P1330
> <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1330r0.pdf>
> Changing the active member of a union inside constexpr
> I need a union in order to implement the std::variant changes in P2231
> <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2231r1.html>
> and a conditionally trivial destructor makes it easier. In order to define
> the __cpp_lib_constexpr_variant macro correctly I need to know if the union
> usage is actually going to work, but there's no macro for P1330, so I can't
> tell.
> A macro for constexpr destructors (P0784R7
> <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0784r7.html>?)
> might have been nice too, because if the compiler doesn't support it then
> you get an error for even trying to declare a destructor constexpr. Without
> a feature test macro there's no reliable way to try to use the feature.

This proposal added __cpp_constexpr_dynamic_alloc.

> If all the compilers I need to support already implemented those features,
> I wouldn't care, but they don't.
> https://godbolt.org/z/qG6d7TxhE
> --
> SG10 mailing list
> SG10_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/sg10

Received on 2021-10-15 17:42:33