You can just use a shared reference to achieve sharing in Rust; you don't need a Box or an Arc. Pretty much every shared core data structure in Rust works fine with references with no Arc in sight, and this makes plenty of sense when you consider that the main way you interact with a type protected by an Arc is by extracting a shared reference from it.
Yes, we are in agreement about that. But they are certainly not necessary for shared data structures (even concurrent ones) and that is what the post to which I was responding said. This also isn't a purely pedantic point; scoped threads and libraries like Rayon are explicitly designed to allow concurrent sharing of values where the sharing has a bounded lifetime, and they do not require reference counting in order to support this (indeed, some usecases of these libraries, such as splitting up arrays into disjoint slices, don't really work with reference counting).
