Nim does allow cycles and the new GC is non-atomic RC + cycle collector.

Though I’ve been hacking on a UI framework written in Nim. Its ui nodes form a tree structure that only tracks parent => child. When it needs the parent info it makes a stack of parents during processing.

Essentially it moves the cycle collector / GC work to extra work during processing. But it’s cheaper since you’re already accessing the memory.

You typically use a weak pointer from child to parent in those situations. So there are no ownership cycles. Languages without garbage collectors (C/C++) pretty much require you to not have ownership cycles or your code will crash during cleanup. Unless you add specific code to detect it and stop it from happening. So I assume you mostly work in GC languages and not C/C++?