I’ve tried doing this a few times in a legacy codebase to contain the definition of `err` when it changes type (this team did not believe in the error interface

I’ve tried doing this a few times in a legacy codebase to contain the definition of `err` when it changes type (this team did not believe in the error interface for awhile). The problem is that it doesn’t stand out visually, and it’s uncommon, so less-experienced team members would have difficulty comprehending what’s going on. In the end we just opted to use two different variables for the two types of error.