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Sebastian wrote: I am just thinking, whether the implicitly contained unique_ptr in your solution should/could be made explicit (e.g. as template argument) instead.

If I understand your question, the simple way to make the implicit unique_ptr in notifying_unique_ptr more explicit would be to not use the notifying_unique_ptr using declaration and write what it represents instead. So instead of writing xnr::notifying_unique_ptr<T, D> you would write std::unique_ptr<T, xnr::notify_ptrs<T, D>>. It is more verbose but that also makes it more transparent about what it is. It isn't hard to guess what is going on - a deleter called notify_ptrs. It could also be more reassuring in code reviews to see that trusted std::unique_ptr explicitly visible.