As sibling comments point out, mutexes aren't needed here. But to answer your direct question, Rust's type system enforces the use of mutexes to access protecte

As sibling comments point out, mutexes aren't needed here. But to answer your direct question, Rust's type system enforces the use of mutexes to access protected values (if you're using the stdlib Mutex implementation) by only allowing access to protected values through a MutexGuard object which is created by locking the mutex. The borrow checker enforces you can't access the MutexGuard concurrently, so therefore you can't access the protected value concurrently.