Explain lifetimes in Rust and when they are needed.

Lifetimes ensure reference validity: • Prevent dangling references • Explicit lifetime annotations • Lifetime elision rules • 'static lifetime for program duration • Generic lifetime parameters Example: fn longest<'a>(x: &'a str, y: &'a str) -> &'a str { if x.len() > y.len() { x } else { y } } // Usage let string1 = String::from("long string"); let string2 = "short"; let result = longest(&string1, string2);