And dependency injection!
Every class needs to use DI for calling other classes, even though we’ll have anyway just a single implementation for all of them, and we won’t be using this flexibility at all (not even for tests where it might be useful for mocking dependencies).



It might be nice to use in some very specific cases (e.g. addition-operation is a binary-operation AST node which is an AST node).
In most of the cases it just creates noise though, and you can usually do something different anyway to implement the same feature. For example in rust, just use enums and list all the possible cases and it’s even nicer to use than inheritance.