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4623. Add feature-test macro __cpp_lib_reflection to <type_traits>

Section: 17.3.2 [version.syn] Status: New Submitter: Ivan Lazaric Opened: 2026-09-17 Last modified: 2026-09-20

Priority: Not Prioritized

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Discussion:

Paper P2996 added feature-test macro __cpp_lib_reflection, exposed only in <meta> (and <version>). It also added entities to <type_traits>, such as std::is_reflection.

The mentioned feature-test macro should therefore be added to <type_traits> as well.

Proposed resolution:

This wording is relative to N5054.

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

   […]
   #define __cpp_lib_reference_wrapper    202403L // freestanding, also in <functional>
   #define __cpp_lib_reflection           202603L // also in <meta>, <type_traits>
   #define __cpp_lib_remove_cvref         201711L // freestanding, also in <type_traits>
   […]