Etienne Kneuss has posted a look at using the SplObjectStorage functionality of the Standard PHP Library as a safe place to tuck away and protect your objects.

In PHP, you basically need two things to safely identify an object: a object index, the handle, and the class handlers which is how the object will react internally. This set of handlers is actually a pointer, and since disclosing valid pointers is not something that should be done, spl_object_hash is simply providing a MD5 hash of those two values concatenated.

Since arrays are hashed when they are created as well, your script is doubling the amount of work it has to do behind the scenes. Instead, Etienne suggests that you use a SplObjectStorage object instead of an array to keep objects inside. The unique identifier for it is then used directly (instead of rehashed, leaving it open for possible referencing collisions) to reference the object.