// exec-env:RUST_POISON_ON_FREE=1

fn main() {
    let mut x = @mut @{f: ~3};
    alt x {
      @@{f: b_x} {
        assert *b_x == 3;
        assert ptr::addr_of(x.f) == ptr::addr_of(b_x);

        *x = @{f: ~4};

        #debug["ptr::addr_of(*b_x) = %x", ptr::addr_of(*b_x) as uint];
        assert *b_x == 3;
        assert ptr::addr_of(*x.f) != ptr::addr_of(*b_x);
      }
    }
}