As I reported in the i.r-l.o prerelease thread, the documentation of the new(ly stabilized) Rc and Arc method new_cyclic could really use some elaboration before the 1.60 release.

I'm quite familiar with refcounting, strong/weak refs, etc. but just from the doc, I have no idea what problem the new method solves exactly, when I should use it, why the closure is needed, how the closure argument seems to come from "thin air", and what the closure should return.