On his blog, Maarten Balliauw has an interesting new post dealing with the use of generics in PHP:

Assuming everyone knows what generics are, let's get down to business right away. PHP does not support generics or something similar, though it could be very useful in PHP development. Luckily, using some standard OO-practises, a semi-generic array can easily be created, even in multiple ways! Here's the road to PHP generics.

He shows the two ways to make generics possible - the hard way (simple inheritance and type hinting) and the more flexible way (a GenericArrayObject that extends the normal ArrayObject to make appending and validating the contents of the array simple).