In a new post to his blog Giorgio Sironi looks at how using dependency injection in your applications can help keep you from writing the same code over and over:

Is Dependency Injection difficult? Is it hard to do? Certainly it provides value. Particularly in Php, but also in other object-oriented languages, Dependency Injection gives steroids to the process of class reuse, designing components as loosely coupled objects.

He explains a bit of what dependency injection is all about, how it fits in with unit testing applications and a few examples of how it might look in some sample PHP classes. He shows how a bit of refactoring can remove dependence of one class on another and how the factory pattern can be used to correctly create an instance your first class might need.