On Fri, 15 Oct 2021 at 23:42, Casey Carter <cartec69_at_[hidden]> wrote:

> 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.
>

Oops, yes, thanks!


>
>> 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
>>
>>
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>