P2781R9 `constant_wrapper`

WG21-P2781R9 constant_wrapper WG21-P3978R3 constant_wrapper Should Unwrap On Call And Subscript WG21-P4206R0 Revert String Support In constant_wrapper LWG-4351 integral-constant-like needs more remove_cvref_t LWG-4383 constant_wrapper's pseudo-mutators are underconstrained LWG-4468 [const.wrap.class] operator decltype(auto) is ill-formed LWG-4500 constant_wrapper wording problems LWG-4523 constant_wrapper should assign to value

Feature-test macro:

#define __cpp_lib_constant_wrapper 202606L

Note: We are not yet accepting PRs for C++26 features.

Also note: WG21-P4206R0 updated the feature-test macro value and said it should be applied "As a DR against C++26". While it wasn't formally voted in that way during the June 2026 meeting in Brno, treating it as a DR is obvious, so I've fused that paper into this tracking issue.