Right. A local reference is escaping the loop scope at the "return". This is safe but weird, and the current borrow checker isn't smart enough to confirm that it's safe. The fancier "Polonius" borrow checker in development is supposed to be less restrictive.

The code example is Rust written as if it were classic C. In Rust, that example would usually be written like this:

    /// Find leading zeros in an array of bytes.
    fn find_leading_0s(bytes: &mut [u8]) -> Option<&mut [u8]> {
        if let Some(pos) = bytes.iter().position(|v| *v != 0 ) { // search
            Some(&mut bytes[..pos]) // find
        } else {
            None // no find
        }
    }

Rust isn't a fully functional language, but the functional features play well with the lifetime system and are optimized well.

(Rust playground example: https://play.rust-lang.org/?version=stable&mode=debug&editio...)