Lifetimes and References

Longest Reference

Returning a Borrow

Lifetime annotations connect the returned reference to the input references it may point at.

Program

Play the program to compare two borrowed strings and return the longer one.

longest_reference.rs 
fn longest<'a>(left: &'a str, right: &'a str) -> &'a str {
    if left.len() >= right.len() { left } else { right }
}

fn main() {
    let left = "rust";
    let suffix = ;
    let winner = longest(left, suffix);
    println!("{winner}");
}

fn longest<'a>(left: &'a str, right: &'a str) -> &'a str {
    if left.len() >= right.len() { left } else { right }
}

fn main() {
    let left = "rust";
    let suffix = ;
    let winner = longest(left, suffix);
    println!("{winner}");
}

fn longest<'a>(left: &'a str, right: &'a str) -> &'a str {
    if left.len() >= right.len() { left } else { right }
}

fn main() {
    let left = "rust";
    let suffix = ;
    let winner = longest(left, suffix);
    println!("{winner}");
}
lifetime parameter `'a` names the relationship between input and output references.
borrow return The function returns one of the borrowed inputs, not a new string.
comparison The branch decides which borrowed value is returned.