As the PHP:Impact blog points out there's a new post from Neil Garb talking about the (loose) coupling going on inside the Zend Framework.

One of the Zend Framework's strongest drawing cards, as I see it, is its loosely-coupled structure. The name Zend Framework may be a misnomer, in fact, as ZF is more a set of reusable libraries than an actual application framework. I won't go into detail about the advantages of loose coupling, but a recent discussion on the ZF mailing list prompted me to investigate just how loosely coupled the framework is.

He's created a few graphs to show the extent of the coupling - a directed graph, the density of it and example code showing deep and shallow coupling. Here's his results.

So, you've just upgraded to PHP 5.2 and all is going well until you come across a page in your application that gives the message "Nesting level too deep - recursive dependency?". With such a vague error message, you might have trouble locating the source of the problem. Thankfully, someone's already been there and figured out the issue - Richard Lord.

I installed PHP 5.2 on one of my testing servers today and a couple of bits of code that previously worked fine in version 5.1.6 threw fatal errors in the new version. The error message was "Nesting level too deep - recursive dependency?" and it took a little time to track down the root of the problem. Here's what I'd done wrong.

Basically, his problem was using the "non-strict" evaluation for checking if two objects were equal to each other (== instead of ===). This compares everything about them, down to the properties - even if they're references to other properties inside of the same class (which is where the problem lies).

So, the fix is simple - === instead of == when comparing those objects. You'll be happier for the change.