clopenset where being empty isn't quite enough

I am aware that the visitor design pattern has been around in some form for years and so what I'm about to write in this post is not particularly innovative or special in any way. I just thought I'd discuss something I've been pondering for a while in my attempts to come up with interesting refactorings for the DuctileJ project.

Anyway, I read

Quite a grandiose title, to be sure, and I'm sure it won't quite live up to all the hype, but I'm pretty pleased with it anyway: katyandrichard.com. Here's a list of its salient features: