Replace public friend operators operator==(), operator!=(), operator<(), etc of QUuid and GUID with friend methods comparesEqual() / compareThreeWay(). Use Q_DECLARE_EQUALITY_COMPARABLE_LITERAL_TYPE, because the (in)equality operators are constexpr. And then we use helper macros, because the other relational operators are not constexpr. Cannot make relational operators constexpr, because it requires to make variant() and isNull() methods constexpr and QT_CORE_INLINE_SINCE. But the experiments show that it does not work with adding constexpr to QT_CORE_INLINE_SINCE. Put relational operators under !QT_CORE_REMOVED_SINCE(6, 8) to prevent an ambiguity. On Windows the metatype for QUuid is created in removed_api.cpp. That leads to an ambiguity, and as a result the compiler fails to create the equals methods of QMetaTypeInterface. This, in turn, leads to the failed comparisons. The usage of !QT_CORE_REMOVED_SINCE(6, 8) solves the problem. Task-number: QTBUG-120304 Change-Id: I640bdeb8f1f7306ba06b9e4193d008cf2bb6dbfb Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>