[littlestymaar]

> So far, I find the language design not super elegant. There are restrictive ownership rules, which are fine, but then a myriad of data structures that let you circumvent these rules. It feels somewhat ad-hoc.

It's not “circumventing” the rules, it's adding automatic runtime check that the invariants are properly maintained when you cannot prove them at compile time.

The default restrictions are here so that you can have safe code without any runtime cost but, every once in a while, such limitation presents you from doing what you want to do. The various data structures you're talking about[1] then make sure that you can write the program you want but that it will not trigger undefined behavior, at the expense of some runtime cost, be it a branch (for RefCell) a reference count increment (Rc, atomic increment for Arc) or a lock.

[1] it's not “a myriad” though, merely 6 of them: Rc & Arc for shared ownership / being 'static, and RefCell, Cell, Mutex and RwLock for shared mutable state)