At no point did I ever indicate that it is impossible for a maintenance coder to accidentally use the wrong variable. In fact, it'll probably happen at some po

At no point did I ever indicate that it is impossible for a maintenance coder to accidentally use the wrong variable. In fact, it'll probably happen at some point. I did indicate that you should have tests in place to catch regressions like this. This is true when you're working with mutable data structures as well as immutable ones. I also indicated this type of error, once detected, is typically very easy to spot and correct. I don't know how anything I've said has even been slightly controversial.