Last month at php|tek I gave a presentation on "How PHP Ticks" where I covered, among other things the process of compiling source code into opcodes (an intermediate psuedo-language similar to what java calls "bytecode" or what .NET calls "MSIL"). As part of this section of the presentation, I showed one of the more interresting changes between ZE 2.0 (PHP 5.0) and ZE 2.1 (PHP 5.1), namely: How variables are retreived and used in an operation. More specifically, how they provide a small, yet cumulative, speedup to applications in a way that's transparent to the end-user -- One more reason to like PHP 5.1 right?
After listening to Marcus Whitney's interview with Brion Vibber of WikiMedia in which he mentions my presentation and makes reference to this engine change, I realized that I should clarify what this feature is (and more importantly, what it isn't) before any FUD spreads.
She describes what they are with an illustration using a simple PHP script and breaking it out into the compiled version's parts - both in PHP4 and the PHP5 versions. Of course, representing what they are needs a flipside, so she presents a look at what they are *not* as well. There's also a brief mention of the special status that globals and static variables get outside the norm.