How to Use the Return Keyword vs Implicit Return in Rust

Use the return keyword to exit a function immediately from any point, and rely on implicit return by placing the final expression at the end of the function body without a semicolon. Use return for early exits in control flow, such as inside loops or conditionals, and use implicit return for the standard flow of the function.

fn first_word(s: &str) -> &str {
    let bytes = s.as_bytes();
    for (i, &item) in bytes.iter().enumerate() {
        if item == b' ' {
            return &s[0..i]; // Explicit return exits early
        }
    }
    &s[..] // Implicit return is the last expression
}

The return keyword acts like a door that immediately kicks you out of a function, while implicit return is simply handing over the last item you touched before the function naturally ends. You use return when you need to stop and leave early, like finding an error or a match, and you use implicit return for the normal result at the very end. Think of return as hitting the 'Stop' button and implicit return as just walking out the front door when you are done.