gistfile1.txt

    resource arc_destruct<T>(data: swappable<~arc_data<T>>) {
        let data = unwrap(data);
        let ptr = ptr::mut_addr_of((*data).count);
        let new_count = rustrt::rust_atomic_decrement(ptr);
        assert new_count >= 0;
        if new_count > 0 {
            unsafe {
                unsafe::forget(data);
            }
        }
        // Otherwise, we are the last one, so we use the normal
        // shutdown proccess.
    }

To create the resource:

type arc_rec<T> = {rc: uint,  data: T};

fn mk_arc<T>(-data: T) -> arc<T> {
    let data = ~{rc: 1u, data: data};
    let ptr: *arc_rec<T> = unsafe::reinterpret_cast(data);
    unsafe::forget(data);
    ret arc(ptr);
}

resource arc<T>(r: *arc_rec<T>) {
    if ref count is zero {
        let ptr: ~arc_rec<T> = unsafe::reinterpret_cast(r);
        // let drop glue take over here
    }
}