struct Body {
    float x
    float y
}

fn push(ptr[Body] b, float dx) {
    b.x += dx
}

fn Body.moved(float dx) -> Body {
    return Body(x: self.x + dx, y: self.y)
}

fn main() {
    b := Body(x: 1.0, y: 2.0)
    push(b, 0.5)                // the same as push(addr(b), 0.5)
    push(addr(b), 0.5)
    print(b.x)
    p := addr(b)
    push(p, 1.0)                // already a ptr: as it is
    print(b.x)
    print(b.moved(1.0).x)
}