rust/chap4/borrow.rs


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/*
 * g1 and g2 here are "references to the m1/m2 variables,
 * I believe they do not point directly to the data address,
 * but to the variables addresses.
 *
 * This makes greet to 'borrow' the reference to the strings,
 * and once the greet() stackframe is gone, m1 and m2 are not
 * freed, just g1 and g2. And since they don't own anything,
 * nothing in the heap is freed.
 */
fn greet(g1: &String, g2: &String) {
    println!("{} {}", *g1, *g2);
}

fn crazy_ref() {

    let x: Box<i32> = Box::new(-1);
    let x_abs1 = i32::abs(*x);
    let x_abs2 = x.abs();
    assert_eq!(x_abs1, x_abs2);

    let r: &Box<i32> = &x;
    let r_abs1 = i32::abs(**r);
    let r_abs2 = r.abs();
    assert_eq!(r_abs1, r_abs2);

    let s = String::from("Howdy");
    let s_len1 = str::len(&s);
    let s_len2 = s.len();
    assert_eq!(s_len1, s_len2);
}

fn main() {
    let m1 = String::from("Howdy");
    let m2 = String::from("partner");

    /*
     * Pass a reference to m1 and m2 to the function parameters.
     */
    greet(&m1, &m2);
    crazy_ref();

}