Are empty abstract classes a bad practice, and why?

Question

We have several empty abstract class in our codebase. I find that ugly. But besides this very stupid reason (ugliness), should I refactor it (into empty interface e.g.) ?

Answer 1

The question to ask is: "What do I want to do with this code that I can't do, or find hard to do, because these empty abstract classes are there?" If the answer is 'nothing', you should leave them alone. If the answer is "something", it may well be worthwhile to remove them - but if you can, speak to the people who created them first, just to make sure there isn't some subtle purpose to them. For example, perhaps your code uses reflection to find all instances of a particular ABC and do special things to them, in which case your refactoring could break the code in subtle ways.