Rust's exclusive ownership can be used for things that can be called at most once (a method can require a non-copyable object as an argument, and takes ownershi

Rust's exclusive ownership can be used for things that can be called at most once (a method can require a non-copyable object as an argument, and takes ownership of it away from you, so you can't call the method again). Rust also has wrapper types like OnceCell that have `get_or_init()` which will init the thing only once, and then it's guaranteed to be immutable. Unlike singletons, these don't have to be globally accessible.