rust question

gistfile1.rs

struct Point {
    x: int,
    y: int
}

fn one() {
    let mut a = ~Point{x: 10, y: 20};
    a.x = 42;
    println(a.x.to_str());
}

fn two() {
    let a = @mut Point{x: 10, y: 20};
    a.x = 42;
    println(a.x.to_str());
}

fn main() {
    one();
    two();
}