> One way to look at reference counting is as a sort of eager, optimized form of garbage collection that works in the case that you have strictly acyclic data (

> One way to look at reference counting is as a sort of eager, optimized form of garbage collection that works in the case that you have strictly acyclic data (or can tolerate leaking cycles). It's interesting to note that python operates with the refcounting + tracing hybrid described (and I know of production deployments where they force the tracing collector to e.g. only run once every N requests because python's never got that fast either). perl, meanwhile, is pure refcounting but has weak references so you can make data acyclic from a refcounting POV at the cost of having to pay attention to which parts of the cyclic structure you keep references to (and for cyclic object graphs there are some tricks you can pull to move the weak link around so you don't have to pay such attention, but that would be a whole comment on its own). koka does refcounting in theory but tries to lift as much of it to compile time as possible in practice, plus if you do e.g. 'y = x + 1' and x has only a single reference to it and is guaranteed to not be used afterwards, it re-uses the storage for y and so can do in-place mutation. nim, meanwhile, offers something called ORC, which is automatic reference counting plus an implementation of Bacon+Rajan's Recycler algorithm which is designed to collect -only- cycles in an otherwise refcounting based system and as such is really rather fast at doing so. Coming back to Rust: There's a stop the world Recycler implementation (rather than concurrent as intended both by the original paper and the author's future plans if the itch returns) here - https://github.com/fitzgen/bacon-rajan-cc https://github.com/fitzgen/bacon-rajan-cc - released as the bacon-rajan-ccc crate from this fork - https://github.com/mbartlett21/bacon-rajan-cc https://github.com/mbartlett21/bacon-rajan-cc - and the README for those contains an Alternative section linking to other experiments in the same area. (I've yet to play with any of the rust versions but love Recycler sufficiently as a concept that I suspect if/when I encounter a situation where it might help I'll be going back and doing so) If you're having trouble finding the Recycler papers, I stashed a copy of each under https://trout.me.uk/gc/ https://trout.me.uk/gc/ (and if you're a similar sort of strange to me, you might also enjoy the ones stashed under https://trout.me.uk/lisp/ https://trout.me.uk/lisp/ ;)