In this new post to his site Joshua Thjissen has shared some of his discoveries with Xdebug, Symfony 2 and problems with maximum nesting levels of objects in his testing.

Here you are, developing your code based on the Symfony2 framework. Creating a form here, add a Twig template there, until suddenly, boom! Your site doesn’t work anymore, and all the info you can find in your PHP logs is [an error about the maximum function nesting level being reached.

[...] What just happened? Did I create some kind of recursive function I wasn’t aware of, did somebody commit code that I accidentally pulled? Fortunately for us developers, there is a quick way to deal with this: google it...

According to the information he found via his search it's a common issue and can be "fixed" by bumping up the max_nesting_level to a higher value. He could have stopped there but he wanted to explain why this problem happened, what the nesting is all about, how it relates to the limitations of XDebug and why Twig could cause problems with it.

Brandon Savage continues his introductory series on exception handling in PHP with this new post to his blog. This time the focus is on methods for nesting exceptions.

In the last two entries we have talked about the concept of layer abstraction: that is, that exceptions should not be allowed to pass out of one layer and into another. So, when an exception is raised in the database layer it should be caught in the controller. But how do we go about making sure that exceptions raised in the database layer are properly recorded and processed, ensuring that we have error logging and don’t simply silence our exceptions?

He looks first at general exception nesting then at extending the base Exception class to write more nested code (inside a class). He also touches on the nested exceptions that were included in the latest release of the PHP 5.3 series.

Mark van der Velden has posted another PHP quiz you can used to test your knowledge of the language:

A short quiz this time, but that doesn't make it less fun. Do you know the answer to all of them? Get a cup of coffee and kill 10 minutes with round two... As always, think of the answer before you execute the code or look it up. You can find round one here.

This one has questions on arrays, ArrayAccess, references, operator precedence and nesting structures. There's no answer key, so you'll just have to test it out if you want to see the answer.

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.

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.