Software systems often need to represent different kinds of a similar thing. I may classify employees by their job type (engineer, manager, salesman), or orders by their priority (rush, regular). My first tool for handling this is some kind of type code field—depending on the language, that might be an enum, symbol, string, or number. Often, this type code will come from an external service that provides me with the data I’m working on. Most of the time, such a type code is all I need. But there are a couple of situations where I could do with something more, and that something more are
...more
