[libcxx-commits] [libcxx] [libc++] P3379R1: Constrain `std::expected` equality operators (PR #117664)

[Xiaoyang Liu via libcxx-commits]

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@@ -1139,7 +1140,11 @@ class expected : private __expected_base<_Tp, _Err> {
 
   // [expected.object.eq], equality operators
   template <class _T2, class _E2>
-    requires(!is_void_v<_T2>)
+    requires(!is_void_v<_T2> &&
+             requires(const _Tp& __tp, const _T2& __t2, const _Err& __err, const _E2& __e2) {
+               { __tp == __t2 } -> convertible_to<bool>;
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xiaoyang-sde wrote:

It seems we used `__boolean_testable` to implement the constraints for `operator==` in `std::reference_wrapper`. (https://github.com/llvm/llvm-project/blob/main/libcxx/include/__functional/reference_wrapper.h#L75-L81)  
Should we consider making them consistent?

https://github.com/llvm/llvm-project/pull/117664