Returning Borrows

But we can also have our function return a reference! This means that a borrow flows back out of a function:

fn identity(x: &i32) -> &i32 {
    x
}

fn main() {
    let mut x = 123;

    let out = identity(&x);

    // x = 5; // 🛠️❌ `x` is still borrowed!

    dbg!(out);
}
This slide should take about 5 minutes.

  • Rust functions can return references, meaning that a borrow can flow back out of a function.

  • If a function returns a reference (or another kind of borrow), it was likely derived from one of its arguments. This means that the return value of the function will extend the borrow for one or more argument borrows.

  • This case is still fairly simple, in that only one borrow is passed into the function, so the returned borrow has to be the same one.