As a PHP developer, I find myself referencing PHP’s source code more and more in my normal everyday work. It’s been very useful in everything from understanding what’s happening behind the scenes to figuring out weird edge-cases to see why something that should be working isn’t. And it’s also very useful in the cases when the documentation is either missing, incomplete or wrong. So, I’ve decided to share what I’ve learned in a series of posts designed to give PHP developers enough knowledge to actually read the C source code behind PHP. No prior knowledge of C should be necessary (we’ll cover some of the basics), but it will help.

This is the first post of the series. In this post, we’ll walk through the basics of the PHP application: where to find it, the general structure of the codebase and a few really fundamental concepts about the C language. To be clear, the goal of the series is to get a reading comprehension of the source code. So that means that at some points in the series, some simplifications will be made to concepts to get the point across without over-complicating things. It won’t make a significant difference for reading, but if you’re trying to write for the core, there is more that will be needed. I’ll try to point out these simplifications when I make them…

Additionally, this series is going to be based off the 5.4 codebase. The concepts should be pretty much the same from version to version, but this way there’s a defined version that we’re working against (to make it easier to follow later, when new versions come out).

So let’s kick it off, shall we?

As any of you who follow the PHP internals list know, scalar type hinting has been a hot topic as of late. You’ll also know that I’ve submitted two new RFC (Request For Comment) proposals for inclusion of two new major features in the PHP language. I figured it was worth going into both RFCs and patches a little deeper, explain my rationale and (hopefully) garner some more visibility of the proposals.

Last night I was discussing the SPL Iterators with @go_oh in the PHP StackOverflow chat room when I came across something very interesting. We were talking about why some of the SPL Iterators accept only an Iterator as the constructor argument (Such as LimitIterator), and others accept either an Iterator or an IteratorAggregate as the argument (Such as IteratorIterator). Feeling that this would be a useful feature to add (having all of them accept an IteratorAggregate), I opened up the PHP source and started looking at how hard of a change this would be. What I found was… Interesting…