NB Comment GB13-309

Author: huixie90

.github/workflows/main.yml

@@ -38,6 +38,7 @@ jobs:
           make concat.html
           make P2483R0.html
           make ref_wrapper_common_ref.html
+          make atomic.html
 
       - name: Deploy 🚀
         uses: JamesIves/github-pages-deploy-action@v4.2.2

README.md

@@ -5,3 +5,4 @@
 - [`any_view`](https://huixie90.github.io/cpp_papers/generated/any_view)
 - [`flat_meow` Fixes](https://huixie90.github.io/cpp_papers/generated/flat_map)
 - [`zip()` Should be an Infinite Range](https://huixie90.github.io/cpp_papers/generated/zip)
+- [Proposed Resolution for NB Comment GB13-309 `atomic_ref<T>` is not convertible to `atomic_ref<const T>`](https://huixie90.github.io/cpp_papers/generated/atomic)

atomic.md

@@ -0,0 +1,69 @@
+---
+title: "Proposed Resolution for NB Comment GB13-309 `atomic_ref<T>` is not convertible to `atomic_ref<const T>`"
+document: PXXXXR0
+date: 2025-10-04
+audience: LEWG, LWG
+author:
+  - name: Hui Xie
+    email: <hui.xie1990@gmail.com>
+  - name: Damien Lebrun-Grandié
+    email: <lebrungrandt@ornl.gov>
+toc: true
+---
+
+
+# Abstract
+
+This paper proposes a converting constructor for `atomic_ref` as the resolution for UK NB Comment GB13-309.
+
+# Introduction
+
+The UK NB Comment GB13-309 pointed out that `atomic_ref<T>` is not convertible to `atomic_ref<const T>`. [@P3323R1] added cv qualifiers to `atomic` and `atomic_ref`. However, the conversion constructor of `atomic_ref` between different cv qualifiers is overlooked.
+
+# Wording
+
+Change [atomics.ref.generic.general]{.sref} as follows:
+
+```cpp
+    constexpr explicit atomic_ref(T&);
+    constexpr atomic_ref(const atomic_ref&) noexcept;
+    @[`template <class U>`]{.add}@
+    @[`constexpr atomic_ref(const atomic_ref<U>&);`]{.add}@
+```
+
+Add a new entry to [atomics.ref.ops]{.sref} after paragraph 8:
+
+:::add
+
+```cpp
+template <class U>
+constexpr atomic_ref(const atomic_ref<U>& ref);
+```
+
+[9]{.pnum} *Contraints*:
+
+- [9.1]{.pnum} `is_same_v<remove_cv_t<T>, remove_cv_t<U>>` is `true`, and
+
+- [9.2]{.pnum} `is_convertible_v<U*, T*>` is `true`
+
+[10]{.pnum} *Postconditions*: `*this` references the object referenced by `ref`.
+
+:::
+
+# Implementation Experience
+
+[@P3323R1] is currently being implemented in libc++ and adding the proposed constructor is under way.
+
+# Feature Test Macro
+
+[@P3323R1] does not seem to mention Feature Test Macro
+
+<style>
+.bq{
+    display: block;
+    margin-block-start: 1em;
+    margin-block-end: 1em;
+    margin-inline-start: 40px;
+    margin-inline-end: 40px;
+}
+</style>