From bb841f20ffb386dcb45981bc4db0b1f2da404a08 Mon Sep 17 00:00:00 2001
From: Ben Deane <ben@elbeno.com>
Date: Mon, 6 Jul 2026 11:09:46 -0600
Subject: [PATCH] :bug: Fix `same_as_unqualified`

Problem:
- Concept subsumption niceties mean that `std::same_as` has to be implemented
  using a helper concept that checks things both ways around.
  `same_as_unqualified` doesn't do this same thing.

Solution:
- Implement `same_as_unqualified` in terms of `same_as`.
---
 include/stdx/concepts.hpp | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/stdx/concepts.hpp b/include/stdx/concepts.hpp
index 17414b9..ea09f8b 100644
--- a/include/stdx/concepts.hpp
+++ b/include/stdx/concepts.hpp
@@ -35,8 +35,13 @@ concept derived_from =
     std::is_base_of_v<U, T> and
     std::is_convertible_v<T const volatile *, U const volatile *>;
 
+namespace detail {
+template <typename T, typename U>
+concept same_as_helper = std::is_same_v<T, U>;
+}
+
 template <typename T, typename U>
-concept same_as = std::is_same_v<T, U> and std::is_same_v<U, T>;
+concept same_as = detail::same_as_helper<T, U> and detail::same_as_helper<U, T>;
 
 template <typename T, typename... Us>
 constexpr auto same_any = (... or same_as<T, Us>);
@@ -45,8 +50,7 @@ template <typename T, typename... Us>
 constexpr auto same_none = not same_any<T, Us...>;
 
 template <typename T, typename U>
-concept same_as_unqualified =
-    is_same_unqualified_v<T, U> and is_same_unqualified_v<U, T>;
+concept same_as_unqualified = same_as<remove_cvref_t<T>, remove_cvref_t<U>>;
 
 template <typename T>
 concept equality_comparable = requires(T const &t) {
@@ -133,8 +137,7 @@ template <typename T, template <typename> typename TypeTrait>
 concept has_trait = TypeTrait<T>::value;
 
 template <typename T, typename U>
-concept same_as_unqualified =
-    is_same_unqualified_v<T, U> and is_same_unqualified_v<U, T>;
+concept same_as_unqualified = same_as<remove_cvref_t<T>, remove_cvref_t<U>>;
 
 template <typename T>
 concept structural = is_structural_v<T>;