How do object hierarchies evolve? Many programmers struggle with this question. Mostly, they want to know how object hierarchies can evolve safely and sensibly! They have a picture in their mind that TDD is only safe in the hands of programmers with excellent design sense, but I believe that anyone can learn these skills with a combination of simple guidelines and guided practice. It would be nice to have more examples. I have stumbled upon one that I’d like to share with you. I’m refacto...
