[libcxx-commits] [libcxx] [libc++] Correct `optional<T&>` implementation (PR #174537)

[Hristo Hristov via libcxx-commits]

================
@@ -1254,6 +1366,77 @@ public:
 #    endif // _LIBCPP_STD_VER >= 23
 
   using __base::reset;
+
+// optional<T&> overloads
+#    if _LIBCPP_STD_VER >= 26
+
+  _LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<_Tp> operator->() const noexcept
+    requires(is_lvalue_reference_v<_Tp>)
+  {
+    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(this->has_value(), "optional operator-> called on a disengaged value");
+    return std::addressof(this->__get());
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp& operator*() const noexcept
+    requires(is_lvalue_reference_v<_Tp>)
+  {
+    _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(this->has_value(), "optional operator* called on a disengaged value");
+    return this->__get();
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp& value() const
+    requires(is_lvalue_reference_v<_Tp>)
+  {
+    if (!this->has_value())
+      std::__throw_bad_optional_access();
+    return this->__get();
+  }
+
+  template <class _Up = remove_cvref_t<_Tp>>
+    requires(is_lvalue_reference_v<_Tp> && is_object_v<__libcpp_remove_reference_t<_Tp>> &&
+             !is_array_v<__libcpp_remove_reference_t<_Tp>>)
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr decay_t<_Tp> value_or(_Up&& __v) const {
+    using _X = remove_cvref_t<_Tp>;
+    static_assert(is_constructible_v<_X, _Tp&>, "optional<T&>::value_or: remove_cv_t<T> must be constructible");
+    static_assert(is_convertible_v<_Up, _X>, "optional<T&>::value_or: U must be convertible to remove_cv_t<T>");
+    return this->has_value() ? this->__get() : static_cast<_X>(std::forward<_Up>(__v));
----------------
H-G-Hristov wrote:

    `using _X = remove_cvref_t<_Tp>;` Why even alias this. I think the code base uses   `remove_cvref_t<_Tp>` inplace.

https://github.com/llvm/llvm-project/pull/174537