I'm going through the interactive version of The Book, and I'm confused by the results of an exercise in Ch 4.3 - Fixing Ownership Errors.

The following code does not work, and they say it's because it would result in the same heap space being deallocated twice:

fn main() {
    let s = String::from("Hello world");
    let s_ref = &s; // reference s
    let s2 = *s_ref; // dereference s_ref
    println!("{s2}");
}

But in my mind, this should be equivalent to the following compilable code, which transfers ownership of s to s2 :

fn main() {
    let s = String::from("Hello world");
    let s_ref = &s; // reference s
    let s2 = s; // move s directly
    println!("{s2}");
}

If s_ref is a reference to s, then dereferencing s_ref should return the String s, shouldn't it? Why can't s be moved to s2 with either the above code or let s2 = *&s;, which fails in the same way?