fn double(ptr[int] p) {
    p.value = p.value * 2
}

fn swap(ptr[int] a, ptr[int] b) {
    t := a.value
    a.value = b.value
    b.value = t
}

fn main() {
    x := 21
    double(addr(x))
    print(x)
    a := 1
    b := 2
    swap(addr(a), addr(b))
    print(a, b)
    p := addr(a)
    pp := addr(p)
    pp.value.value = 99
    print(a)
    ptr[int] none = null
    print(none == null, p != null, none)
}