Refactoring: Narrow ↔ Widen Parameter

I decided to just plow through the whole catalog of refactorings. They are all useful, but they aren’t so exciting to write. Boo hoo. I need to get them done, & not writing them will never get them done.

I’d love feedback on this one. Implementing the refactoring is a little tricky (but fun, for me anyway). Do you get it? How about the discussion of aggr…