[libcxx-commits] [libcxx] [libc++] P2944R3: Constrained comparisions - `variant` and `tuple` (PR #141396)

[Nikolas Klauser via libcxx-commits]

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@@ -1153,9 +1154,16 @@ struct __tuple_equal<0> {
 };
 
 template <class... _Tp, class... _Up>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Tp& __t, const _Up& __u) {
+            { __t == __u } -> __boolean_testable;
+          } && ...) && (sizeof...(_Tp) == sizeof...(_Up))
+#    endif
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 operator==(const tuple<_Tp...>& __x, const tuple<_Up...>& __y) {
+#    if _LIBCPP_STD_VER < 26
   static_assert(sizeof...(_Tp) == sizeof...(_Up), "Can't compare tuples of different sizes");
+#    endif
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philnik777 wrote:

I'm seeing this from the other side actually. It's guarded, so my first instinct is to wonder whether this restriction has been lifted in C++26. Just having the `static_assert` unconditionally tells the reader that it's always a requirement. Whether this is enforced through a constraint as well doesn't really bother me that much.

https://github.com/llvm/llvm-project/pull/141396