Shared box and unique box

boxing.rs

use std;
import std::io::println;
fn main() {
    // shared box
    let i = @mutable 10;
    println(int::str(*i)); // => 10
    let j = i;
    *j = 20;
    println(int::str(*i)); // => 20
    // unique box
    let i = ~mutable 10;
    println(int::str(*i)); // => 10
    let j = i;
    *j = 20;
    println(int::str(*i)); // => 10
}