Interesting idea with the union and using typeof(). We (I) went with large macros defining wrappers instead, which, I believe, is a necessity with intrusive data structures, or at least I don't immediately see how to do that with unions & typeof. Maybe it's possible...?

e.g. hash table wrapper: https://github.com/FRRouting/frr/blob/master/lib/typesafe.h#...

(cf. https://docs.frrouting.org/projects/dev-guide/en/latest/list...)