[libcxx-commits] [libcxx] [libc++] Reimplement `optional<T&>` as a partial specialization (PR #201983)

[William Tran-Viet via libcxx-commits]

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@@ -1343,24 +1220,137 @@ public:
 #    endif // _LIBCPP_STD_VER >= 23
 
   using __base::reset;
+};
 
-// optional<T&> overloads
 #    if _LIBCPP_STD_VER >= 26
+template <class _Tp>
+class optional<_Tp&> : public __optional_iterator_base<_Tp&> {
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smallp-o-p wrote:

For `__optional_iterator_base`, we need `optional::iterator`, which inherits in that long chain of empty bases all the way to `__optional_storage_base`. There is a lot of room for simplification there by making `__optional_iterator_base` inherit directly from the storage base, but I think that should go in a different patch to not bloat this one.

https://github.com/llvm/llvm-project/pull/201983