In the first part of a new series over on DevShed.com, they introduce the concept of "segregated interfaces" and show how to use them to work with collections of arrays (using interfaces that are a part of the SPL).
To start illustrating why segregated interfaces are really useful, in the lines to come I'm going to build an example that will recreate the scenario described in the introduction. Basically, what I want to achieve here is to construct a custom countable array collection.
He shows the basic class structure needed to emulate a countable array in an object by implementing the "Countable" interface. He adds in the "Iterator" interface to allow you to work with the dataset like an array - progressing through it, rewinding to the beginning and checking to see if a value exists. Finally, they add the "ArrayAccess" interface to the class that boosts it with even more features like the ability to grab things by specific keys (numeric or string). The finish the article off with an example of an ArrayCollection object and how it can be looped through using a foreach.