On Mon, 15 Jun 2020 at 15:24, Barry Revzin <barry.revzin@gmail.com> wrote:


On Mon, Jun 15, 2020 at 5:45 AM Jonathan Wakely via SG10 <sg10@lists.isocpp.org> wrote:
Please see the 2018 thread below. I think this macro should be added to SD-6 and the IS, and I think it should also be updated to 201811L for the P1032R1 "Misc constexpr bits" changes that made the remaining char_traits members constexpr. All the other bits of P1032R1 have their own macro now instead of __cpp_lib_constexpr_misc, but not the char_traits bits.

Libstdc++ has been defining __cpp_lib_constexpr_char_traits to 201611 for years (and I'm about to update the value to 201811 in the relevant branches).

Any objection before I open an LWG issue?



It could do, but it affects string_view equally.

I suppose we could say that the current values for constexpr_string and constexpr_string_view also assume support for constexpr in char_traits, so that implementations should not define the latest values until they've done the char_traits parts.

So we'd have three possible values for constexpr_string, 201611 for P0436, 201811 for P1032, and 201907 for P0980 (which is already there). And two values for constexpr_string_view, 201611 for P0436 and 201811 for P1032 (which is already there).

I can send a pull request to do that if you like.