Rust Supports Custom Method Receivers Beyond &self and &mut self

Rust's ownership system extends beyond the commonly used &self and &mut self method receivers to include arbitrary self types such as self: &Arc and self: &Mutex. These specialized receivers are rarely seen in everyday application code but become valuable when designing concurrent and multi-threaded systems. Standard receivers cover shared borrowing, exclusive mutable borrowing, and full ownership transfer, while arbitrary self types allow methods to directly require smart-pointer wrappers. For example, a method declared with self: &Arc can internally clone the Arc and spawn async tasks without the caller needing to handle the clone explicitly. This feature lets developers encode thread-safety requirements directly into method signatures, making concurrent Rust APIs more expressive and harder to misuse.