Adam Gotterer has written up a tutorial with his process behind creating an object collection manager with PHP's built-in SPL functionality.

The purpose of a collection is to store objects in an organized manner with specific access rules. We are going to build a collection class using the Standard PHP Library (SPL). Our final product will be capable of iterating, counting and access to objects via array. If you are not familiar with SPL you can find some additional information on the PHP SPL manual site. Unfortunately the manual is somewhat lacking.

He creates an object that implements the ArrayAccess, Countable and Iterator objects to create a "Collection" class to hold his multiple objects inside an"objects" array. He includes some code to test the class and the output as a result.