Lifetimes and Ownership Revisited

Lifetimes prevent dangling references and ensure memory safety.

Why Lifetimes?

To ensure references are valid as long as needed.

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}

Here, 'a is a lifetime parameter stating both inputs and output share the same lifetime.

Rust usually infers lifetimes, but in complex cases, you specify them explicitly.