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### 3349. Missing `__cpp_lib_constexpr_complex` for P0415R1

Section: 17.3.2 [version.syn] Status: C++20 Submitter: Stephan T. Lavavej Opened: 2019-12-04 Last modified: 2021-02-25

Priority: 0

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Discussion:

P1902R1 "Missing feature-test macros 2017-2019", accepted in Belfast, said:

> [P0415R1] (Constexpr for `std::complex`): this paper proposes to introduce the macro `__cpp_lib_constexpr_complex`. That is, introducing a new macro for this header.

However, `__cpp_lib_constexpr_complex` wasn't mentioned in the Wording section, and doesn't appear in the latest WP N4842.

P0415R1 was accepted in Albuquerque (November 2017), and the paper itself said "For the purposes of SG10, we recommend the feature-testing macro name `__cpp_lib_constexpr_complex`.", so this has been accepted and then overlooked by WG21 twice.

[2019-12-12 Issue Prioritization]

Status to Tentatively Ready and priority to 0 after twelve positive votes on the reflector.

Proposed resolution:

This wording is relative to N4842.

1. Modify 17.3.2 [version.syn] p2 as indicated:

   >     […]
   >     #define __cpp_lib_constexpr_algorithms    201806L // also in <algorithm>
   >     #define __cpp_lib_constexpr_complex       201711L // also in <complex>
   >     #define __cpp_lib_constexpr_dynamic_alloc 201907L // also in <memory>
   >     […]