To more explicitly state what other monks have already alluded to:

Cookies only store strings. Period. You can't put a reference into a cookie, only a string, so the reference gets stringified into ARRAY(0xDEADBEEF) when you try to put it into the cookie.

If you want to store non-string information in a cookie, you must convert it to a string and then convert it back from that string into a usable form when the user agent sends the cookie back to you.