One of PHP5's most interesting new features is the addition of Iterators, a collection of ready-made interfaces designed to help in navigating and processing hierarchical data structures. These Iterators significantly reduce the amount of code required to process an XML document tree or a file collection.

They give three examples - two basic ones showing a simple use of the DirectoryIterator and RecursiveDirectoryIterator and another slightly more complex one showing how to get information from the recursive iteration as it goes down.

It's a generally accepted fact that more readable code is more maintainable and easier for other developers to pick up. [...] Today I'm going to take a look at object iteration, most commonly found in the Standard PHP Library, and explore using the Iterator interface to simplify looping.

The main part of the tutorial shows how to implement the Iterator interface of the SPL to create your own custom methods, theirs being a Database version with methodsfor rewinding, reading and getting the current record you're working with.

As an application developer, you can have a lifelong career without ever knowing what any of the patterns are called or how or when they're used. However, I've found that a good working knowledge of these patterns, as well as those introduced in the developerWorks article "Five common PHP design patterns" (see Resources), allows you to do two things: Enable high-bandwidth conversations and reduce painful lessons.

The patterns they talk about in this "five more" article of the series are:

• Adapter Pattern
• Iterator Pattern
• Decorator Pattern
• Delegate Pattern
• State Pattern

Diagrams are provided for each of them, showing how they flow along with brief code examples (structures really) to show how that transitions over to actual use.

The PHP 5 Iterator interface is very useful for defining custom behaviour for looping over objects, however I just noticed that looping over such objects in Smarty will not work correctly. Smarty will in fact cast an object back to an array.

He includes code examples of his problem to illustrate and shows how he got around the problem - a getData() function he defined that just returns the array from the object.