fn divide(a: i32, b: i32) -> Result<i32, String> {
    if b == 0 {
        Err("divide by zero".to_string())
    } else {
        Ok(a / b)
    }
}

fn main() {
    println!("{:?} {:?}", divide(10, 2), divide(1, 0));
}

the built-in enum for success or error