What does this Rust snippet output?

1struct Rect { w: u32, h: u32 }
2impl Rect {
3    fn square(s: u32) -> Rect { Rect { w: s, h: s } }
4    fn area(&self) -> u32 { self.w * self.h }
5}
6fn main() {
7    let r = Rect::square(4);
8    println!("{}", r.area());
9}