Why avoid subtyping?

Question

I have seen many people in the Scala community advise on avoiding subtyping \"like a plague\". What are the various reasons against the use of subtyping? What are the altern

Answer 1

One reason is that equals() is very hard to get right when sub-typing is involved. See How to Write an Equality Method in Java. Specifically "Pitfall #4: Failing to define equals as an equivalence relation". In essence: to get equality right under sub-typing, you need a double dispatch.