What is borrowing in Rust and what are the borrowing rules?

Borrowing allows references without taking ownership: • References don't take ownership • Multiple immutable references allowed • Only one mutable reference at a time • No mixing mutable and immutable references • References must be valid (no dangling) Example: fn main() { let mut s = String::from("hello"); let r1 = &s; // immutable borrow let r2 = &s; // OK: multiple immutable let r3 = &mut s; // Error: can't borrow as mutable }