Listing 4-6 is unclear

[qucchia]

The purpose of listing 4-6 is to explain how references aren't necessarily mutable:

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

    change(&s);
}

fn change(some_string: &String) {
    some_string.push_str(", world");
}

However, the point may be unclear as s is declared as immutable anyway, so the user who has read the previous sections wouldn't expect this to compile in the first place. The second line should be changed to

    let mut s = String::from("hello");

in order to make the point better.

[Halloloid]

yaa the purpose of this code is to show error that happend bcoz the s was not declared mutable so this correct i think we no need to change i think