Lifetimes

Elision covers most

Most functions need no lifetime names because the compiler fills them in. A function that takes one shared borrow and returns one shared borrow just works:

fn first(s: &str) -> &str { s }

One named lifetime (&'a form)

When two borrows enter and one borrow leaves, name the relationship once. Both inputs and the output share the same name to show they live together:

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

Static strings

String literals live for the whole program and use the static lifetime. A static borrow never expires while the program runs:

let s: &'static str = "hello";

Read compiler hints

When a lifetime is missing, the compiler suggests one exact spot to add it. Read the hint, add the name, and keep the change small:

let s = String::from("hi"); let r = s.as_str(); println!("{}", r);

Next: Functions

Article author: Arthur Isaev