In this new tutorial on the TopTal.com site author Agustin Villalba takes an in-depth look at how objects and references are handled in memory by the PHP language.

In this article, I will talk about how object and variable references are controlled in memory, since this is an issue that can generate discussion and differing opinions. One question to ponder is: “By default, are objects passed by reference or by copy in PHP?” I’m going to talk first about what references are not in PHP; secondly, I’ll discuss what they are, and finally, I will examine how the garbage collector works in PHP.

He starts with a quick comparison between objects and references (since they're slightly different). He then covers what things are and aren't references in PHP and some examples showing what they are in either case. Code examples and visuals are included showing how things relate. The post wraps up with a look at how garbage collection works with objects/references and a few closing thoughts about how the collector chooses which to clean up.