• "The Power of PECL" by Simon Holywell
• "Be 'ready' if you want to be done!" by Steffan Surdek
• "All Data is Relational" by Cory Isaacson
• "Fixing PHP Production Problems with APM" by Dan Delany and Chris Kelly
• "Trust" by Sebastian Bergmann

You can download your copy for free from their site and catch up on back issues.

Turns out that variables called as functions must be an instance of Closure, an instance of a class which implements __invoke(), or a string representing a named function in the global namespace. In the anonymous function body above, $fibonacci is none of these. It is an undeclared, free variable in the closure created by the anonymous function. At the time when it's called, it hasn't been bound-hence the Notice that you would have gotten if error reporting were set at a high enough threshold - and therefore can't be called as anything, let alone as a function.

He tried using the "use" functionality PHP closures have to bring a variable/object/etc into the scope of the running function, but it still threw an error. As it turns out, the combination of "use"-ing the object and calling it by reference handles things correctly. He takes this method and applies it in two examples - one call in an array_map function and another in an array_reduce.

PHP has different in-core callbacks able to help us with daily deployment, debug, improvements. At the same time, PHP is loads of intrinsic "gotcha", too often hard to understand, hard to explain, or simply hard to manage. One common problem is about debug, caching, or freezing, and the way we would like to debug, cache, or freeze, variables.

He presents the problem - serializing variable information to "freeze" it and how recursion can cause problems down the line. He looks at the two different kinds of recursion (recursion and recursion by reference) and, after looking at a few possible solutions to fix things, eventually comes down to a way to remove the recursion "without losing it".

However, because we as PHP developers are lazy, provide a few GDB tricks to make this easier. First of all, it's only really going to work if you haven't stripped the symbols from your PHP and Apache binaries. Secondly, you still need to have the PHP source lying around somewhere.

He suggests using GDB to run the backtraces and create a file to help you track down the infinite recursion problem that could be giving you issues.

One of the requirements [of the original Set::extract method] was that the new method would need to be faster or at least as fast as the old implementation. My first attempts were big failures. Not only did the solutions I came up with contain tons of bugs. No, they were are also a lot slower the old extract function. A few benchmarks later and I discovered the biggest bottleneck in my implementation: Recursiveness.

He notes that no doing things recursively (not just in this situation, but ever) can help with a speed boost. In his example, a small change made all the differences and the XPath implementation in the CakePHP core makes grabbing information from any array simple.

While the implementation does not support full XPath (and probably won't in future), feel free to make suggestions on additional selectors or the idea in general.

If the software calls for only 2 levels of categorization (Parent and Child only), a simple nested for loop will suffice. However, software requirements change and you'll soon find yourself up shit creek without a paddle if you need to support 3 or 4 levels of nesting. [...] To those who's training is less formal (most web developers I meet have practical training, not formal), I'll help you out: Tree Traversals (or if you are completely lost, Recursion).

He creates a recursive function that, when passed in a category set with different types in it, can handle each of them and then calls itself again with the new child data. His sample code creates url out of a set of categories.

Using what they've taught in the first two parts of the series, they put it to good use, giving you a step-by-step guide to a simple recursive forum. They start with the database structure (always a good thing) and work out from there, creating the "ThreadProcessor" class and fetch functionality to grab the thread's contents. They also include a bit of functionality to create threads as well. It's not much more than that, so don't expect too much, but it is a great place to start.

The two he shares are this guide to recusion from DevShed and a guide from Builder.com on the creation of graphics on the fly.

They start with a simple example of OOP with recursion, handling some "HTML widgets" to be output to a page (div, h1, p, and ul tags). With this library created and in place, they work up a "generator" class to actually build the page dynamically. Finally, they bring it all together with the creation of a simple template processor for simple page creation.

If you've never used recursion, you're in luck - they start from the very beginning, explaining it with a simple example of pushing the entire contents of an array (with subarrays) out to a file. They use this exmaple as a base to improve the function, adding the function to write the data out. They finish it off with two handy recursive functions for everyday use - one to escape the entire contents of an array and one that does the same, but checks to see if magic quotes is on.