[libcxx-commits] [libcxx] [libc++] Implement P3168R2: Give optional range support (PR #149441)

[A. Jiang via libcxx-commits]

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@@ -579,16 +607,49 @@ struct __is_std_optional : false_type {};
 template <class _Tp>
 struct __is_std_optional<optional<_Tp>> : true_type {};
 
+template <class _Tp, class = void>
+struct __optional_iterator_aliases {};
+
+#    if _LIBCPP_STD_VER >= 26
+// disallow T (&)() and T (&)[]
+template <class _Tp>
+struct __optional_iterator_aliases<
+    _Tp,
+    __enable_if_t<!(is_reference<_Tp>::value && (is_function<__libcpp_remove_reference_t<_Tp>>::value ||
+                                                 is_unbounded_array<__libcpp_remove_reference_t<_Tp>>::value))> > {
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frederick-vs-ja wrote:

See [LWG4304](https://cplusplus.github.io/LWG/issue4304). I think I was just too nervous about `optional<NonReturnable&>`, maybe it's better to delay adding then special handling during implementing `optional<T&>`.

https://github.com/llvm/llvm-project/pull/149441