[libcxx-commits] [libcxx] [libc++] Fix constraint recursion in std::expected's operator== (PR #201455)

[Nikolas Klauser via libcxx-commits]

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@@ -1161,8 +1161,11 @@ class expected : private __expected_base<_Tp, _Err> {
     }
   }
 
-  template <class _T2>
-  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const _T2& __v)
+  // The unusual signature avoids constraint recursion via ADL through
+  // std::expected, see https://github.com/llvm/llvm-project/issues/160431.
+  template <class _T2, class _Tp2>
+    requires _IsSame<_Tp2, _Tp>::value
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected<_Tp2, _Err>& __x, const _T2& __v)
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philnik777 wrote:

```suggestion
  template <class _T2, same_as<_Tp> _Tp2>
```

https://github.com/llvm/llvm-project/pull/201455