struct Config {
    name: String,
    retries: u32,
}

// borrow the whole struct, touch only the name
fn name_len(c: &Config) -> usize {
    c.name.len()
}

fn main() {
    let c = Config { name: "prod".into(), retries: 3 };
    println!("{} {}", name_len(&c), c.retries);
}

take &self and read what you need