Rust中的所有权，引用和借用

fn main() {
    let mut s = String::from("hello");
    s.push_str(", world!");
    println!("{}", s);

    let s1 = String::from("hello");
    let (s2, len) = calculate_len(s1);
    println!("The len of ‘{}‘ is {}.", s2, len);

    let s1 = String::from("hello");
    let len = calculate_length(&s1);
    println!("The length of ‘{}‘ is {}.", s1, len);
}

fn calculate_len(s: String) -> (String, usize) {
    let length = s.len();
    (s, length)
}


fn calculate_length(s: &String) -> usize {
    s.len()
}