Well, if you're talking about named instance variables in Smalltalk, not much.

The other night, I had a zany idea about instance variables. This blog is not about that. I haven't realized said zany idea, yet. As I looked at it, I found that I really wanted real world objects to represent and reify those slots that are defined in ClassDescription. The current implementation is just an array of strings. Any reflection about a classes instance variables is done through APIs on the Class (things like indexOfInstVar: 'foobar', etc). But no real objects to represent and reflect about instance variables directly.

It seemed like it might be fun to build such a thing and then explore what we could do with them. I also missed doing some ground up, test focused, development. So I sat down and wrote some tests. Then I used the debugger to fill out the code. After 6 tests and some code, I can ask a class for its namedSlots. It answers back a collection of NamedSlot objects. There's not much to them right now. They're kind of like CompiledMethods, an mclass and a name. You can ask one for its index.

If all goes as planned, I'll try to explore what can be done with these in the next few days. The code for just this little bit is published as NamedSlots and NamedSlotsTests. Feel free to follow along.

Smalltalk is one of the only languages out there that not only has really rich reflection, but actually allows you to add more to it.