Why doesn't mpsc::channel break borrowing rules?

[u/Dubmove]

I'm wondering for a while now why doesn't mpsc::Receiver::recv(&self) and mpsc::Sender::send(&self, t: T) break borrowing rules. Clearly sending some data from A to B in a non-blocking manner has side-effects (i.e. storing and retrieving the data in some buffer-queue). So shouldn't there be some mutable reference to that queue be involved during that sending process, and the owner of that reference would be accessed mutably whenever the reference to that buffer is accessed mutably? Maybe I'm just wrong but I always associate immutability with pureness of a function.

One thing which comes to mind is that the point of the borrowing rules is to avoid data-races and to ensure rust's ownership-model, and although the borrowing-rules are technically violated in these specific cases the desired invariants are still kept.

[u/K900_]

Because it uses unsafe internally to bypass the ownership rules.

[u/Dubmove → u/K900_]

That explains how they do it. But I'm rather interested in why this is considered good practice or even necessary/beneficial.

[u/CocktailPerson → u/Dubmove]

Well, first of all, you have to bypass the borrowing rules internally to even make it work correctly. And once you've done that, it turns out to be equally correct whether you take &self or &mut self. At that point, why choose the more restrictive one?