@jonathanhogg Absolutely not comparable `Arc<Mutex<>>` gives shared access to mutable content, `Arc::make_mut()` is clone-on-write, so you mutate ONLY the copy, changes not reflected anywhere else; all `Weak` pointers are invalidated.

@michalfita you’ll find that I didn’t say they were comparable, just that the latter is thinly documented. Copy-on-write was exactly the behaviour I needed and a Mutex was how I was hacking it first time round