Code shared from the Rust Playground

playground.rs

fn main() {
    let s = String::from("book");

    let ss = pluralize(s.clone());
    println!("One {}, many {}", s, ss);
}

fn pluralize(s: String) -> String {

    // Can't push_str directly onto s as s is not mutable
    let mut p = s;
    p.push_str("s");
    return p

// This is ok
//    s + "s"
}