Marco Pivetta has posted about an interesting trick you can do with closures in PHP related to accessing private properties inside classes.
A couple of weeks ago I was working on a very tricky issue on ProxyManager. The problem is simple: instantiating ReflectionClass or ReflectionProperty is slow, and by slow, I mean really slow! The reason for this research is that I'm trying to optimize a "hydrator" to work with larger data-sets by still keeping a low initialization overhead. PHP 5.4 comes with a new API for Closures, which is Closure#bind(). Closure#bind() basically allows you to get an instance of a closure with the scope of a given object or class. Neat! That's basically like adding APIs to existing objects! Let's break some OOP encapsulation to fit our needs.
He shows how to use this "bind" feature to reach into an object, in this case a "Kitchen", and extract the value of an internal, private property. He also talks some about the performance of this method versus the more typical use of Reflection. He includes two other quick examples too - accessing the same private properties by reference and an abstracted "property reader" closure that uses the bind trick on any object.