[giornogiovanna]

- Doubly linked lists.

- Cocoa delegates that keep references to some parent of the objects that they're delegates of.

- Some event listeners (in the same way as delegates).

I wouldn't say it's "rare". It popped up pretty often for me when I was writing Objective C.

[azinman2]

What’s not solved with weak refs?

[ben-schaaf]

What's not solved with manual memory management? The point is not that you can't solve it, the point is that reference counting isn't the whole solution for garbage collection unlike a tracing gc for instance.

[saagarjha]

Weak reference counting is still reference counting.

[giornogiovanna]

It can always be solved with weak references.

[fauigerzigerk]

Only if you know that you haven't solved it already: https://news.ycombinator.com/item?id=19093677