Use Milian's asTuple() trick and compareThreeWayMulti(). The pointer variable presents a challenge, because, like op<, op<=> cannot order unrelated pointer values. Trying to is UB; one is supposed to use std::less and std::compare_three_way instead, but, you guessed it, less<tuple<T*>> uses op< to compare the tuples, which, in turn uses op< on the T* member, causing UB. [ChangeLog][QtCore][QtCompare] Added a Qt::totally_ordered_wrapper class whose relational operators use the std ordering types. Use it to wrap the pointers when doing the comparison to avoid UB. This allows a smooth migration once we depend on C++20 and class authors start using lhs.asTuple() <=> rhs.asTuple() or even start to =default op<=>. The wrapper type is robust against all these transformations. Update QModelIndex comparison documentation part. Task-number: QTBUG-117660 Change-Id: I126b2ebff458800134ed6e774a389d85d76a395f Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>