Show how ownership in Rust works

main.rs

/// See link more details:
/// https://doc.rust-lang.org/book/ch04-01-what-is-ownership.html
fn main() {
    // String is made up of the following:
    // - pointer to string contents
    // - length
    // - capacity
    let s1 = String::from("hello");

    // immutable transfer from s1 to s2
    let s2 = s1;

    // mutable transfer from s2 to s3
    let mut s3 = s2;
    s3.push_str(", world!");

    // immutable transfer from s3 to s4
    let s4 = s3;

    // println!("{}", s3);
    // println!("{}", s2);
    // println!("{}", s1);

    // immutable borrow of s4 by fn
    let s4_len = calculate_length(&s4);
    println!("s4 => '{}'", s4);
    println!("length(s4) => {}", s4_len);

    // s4 is still an owner after clone
    let mut s5 = s4.clone();

    // s4 and s5 are not the same
    s5.push_str(" hasta la vista.");
    println!("s4 => '{}', s5 => '{}'", s4, s5);

    // immutable transfer from s5 to fn
    let s5_len = calculate_length_borrow(s5);
    println!("length(s5) => {}", s5_len);
    // println!("s5 => {}", s5);
}

/// Calculate length with reference
fn calculate_length(s: &String) -> usize {
    s.len()
}

/// Calculate length with borrowing
fn calculate_length_borrow(s: String) -> usize {
    s.len()
}