[libcxx-commits] [PATCH] D99817: [libcxx] applies LWG3175

[Christopher Di Bella via Phabricator via libcxx-commits]

cjdb created this revision.
cjdb added reviewers: zoecarver, curdeius.
cjdb requested review of this revision.
Herald added a project: libc++.
Herald added a subscriber: libcxx-commits.
Herald added a reviewer: libc++.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D99817

Files:
  libcxx/docs/Cxx2aStatusIssuesStatus.csv
  libcxx/include/concepts
  libcxx/test/std/concepts/concepts.lang/concept.swappable/swappable_with.compile.pass.cpp


Index: libcxx/test/std/concepts/concepts.lang/concept.swappable/swappable_with.compile.pass.cpp
===================================================================
--- libcxx/test/std/concepts/concepts.lang/concept.swappable/swappable_with.compile.pass.cpp
+++ libcxx/test/std/concepts/concepts.lang/concept.swappable/swappable_with.compile.pass.cpp
@@ -15,6 +15,7 @@
 #include <concepts>
 
 #include <array>
+#include <cassert>
 #include <deque>
 #include <forward_list>
 #include <list>
@@ -644,4 +645,43 @@
 static_assert(!check_swappable_with<HasANonMovable, HasANonMovable>());
 } // namespace types_with_purpose
 
+namespace LWG3175 {
+// Example taken directly from [concept.swappable]
+template <class T, std::swappable_­with<T> U>
+constexpr void value_swap(T&& t, U&& u) {
+  std::ranges::swap(std::forward<T>(t), std::forward<U>(u));
+}
+
+template <std::swappable T>
+constexpr void lv_swap(T& t1, T& t2) {
+  std::ranges::swap(t1, t2);
+}
+
+namespace N {
+struct A {
+  int m;
+};
+struct Proxy {
+  A* a;
+  constexpr Proxy(A& a) : a{&a} {}
+  friend constexpr void swap(Proxy x, Proxy y) {
+    std::ranges::swap(*x.a, *y.a);
+  }
+};
+constexpr Proxy proxy(A& a) { return Proxy{a}; }
+} // namespace N
+
+[[nodiscard]] constexpr bool CheckRegression() {
+  int i = 1, j = 2;
+  lv_swap(i, j);
+  assert(i == 2 && j == 1);
+
+  N::A a1 = {5}, a2 = {-5};
+  value_swap(a1, proxy(a2));
+  return a1.m == -5 && a2.m == 5;
+}
+
+static_assert(CheckRegression());
+} // namespace LWG3175
+
 int main(int, char**) { return 0; }
Index: libcxx/include/concepts
===================================================================
--- libcxx/include/concepts
+++ libcxx/include/concepts
@@ -326,7 +326,7 @@
 
 template<class _Tp, class _Up>
 concept swappable_with =
-  common_reference_with<_Tp&, _Up&> &&
+  common_reference_with<_Tp, _Up> &&
   requires(_Tp&& __t, _Up&& __u) {
     ranges::swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Tp>(__t));
     ranges::swap(_VSTD::forward<_Up>(__u), _VSTD::forward<_Up>(__u));
Index: libcxx/docs/Cxx2aStatusIssuesStatus.csv
===================================================================
--- libcxx/docs/Cxx2aStatusIssuesStatus.csv
+++ libcxx/docs/Cxx2aStatusIssuesStatus.csv
@@ -194,7 +194,7 @@
 "`3050 <https://wg21.link/LWG3050>`__","Conversion specification problem in ``chrono::duration``\  constructor","Prague","",""
 "`3141 <https://wg21.link/LWG3141>`__","``CopyConstructible``\  doesn't preserve source values","Prague","",""
 "`3150 <https://wg21.link/LWG3150>`__","``UniformRandomBitGenerator``\  should validate ``min``\  and ``max``\ ","Prague","",""
-"`3175 <https://wg21.link/LWG3175>`__","The ``CommonReference``\  requirement of concept ``SwappableWith``\  is not satisfied in the example","Prague","",""
+"`3175 <https://wg21.link/LWG3175>`__","The ``CommonReference``\  requirement of concept ``SwappableWith``\  is not satisfied in the example","Prague","|Complete|","13.0"
 "`3194 <https://wg21.link/LWG3194>`__","``ConvertibleTo``\  prose does not match code","Prague","",""
 "`3200 <https://wg21.link/LWG3200>`__","``midpoint``\  should not constrain ``T``\  is complete","Prague","|Nothing To Do|",""
 "`3201 <https://wg21.link/LWG3201>`__","``lerp``\  should be marked as ``noexcept``\ ","Prague","|Complete|",""


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