On the Ibuildings blog today, Harrie Verveer has posted about an interesting quirk he found when working with objects and references:

PHP is a loosely typed language. Most of the time this is very useful because you as a programmer don't have to worry about typecasting: it's done for you. However, on some occasions this can cause some unexpected trouble. [...] In this blog I want to point out what can happen if you try to access object properties by reference when the object is not initialized.

His example shows the problem when it tries to grab a value from an array in a non-existent object by reference. It results in a dyanamically created object (of that type) with an empty array inside of it. It only works when you grab it by reference, but he shares a tip or two about how you can prevent hard to track down issues like this.