[libcxx-commits] [libcxx] [libc++] LWG4324: `unique_ptr<void>::operator*` is not SFINAE-friendly (PR #190919)

[A. Jiang via libcxx-commits]

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@@ -117,6 +117,12 @@ struct __unique_ptr_deleter_sfinae<_Deleter&> {
   typedef false_type __enable_rval_overload;
 };
 
+template <class, class = void>
+inline const bool __can_dereference = false;
+
+template <class _Tp>
+inline const bool __can_dereference<_Tp, decltype((void)*std::declval<_Tp>())> = true;
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frederick-vs-ja wrote:

It's not very easy to deduplicate them. Currently, `unique_ptr::operator*` permits the underlying `operator*` to return `void` (which is a bit pathological, though). However, `__dereferenceable` requires the underlying `operator*` to return a reference or object type.

https://github.com/llvm/llvm-project/pull/190919