Why is “abstract override” required not “override” alone in subtrait?

Question

I read the section of Programming in Scala where abstract override is introduced, but I\'m still confused by what exactly is signified by the joining of these m

Answer 1

The idea is that it's an incomplete override -- you still want to require the eventually concrete implementation of the trait to provide that method, even though you're modifying that hypothetical method's behavior. In other words, the method you're overriding isn't a full standalone implementation. It gives a similar effect as a method decorator might in Python.

As far as I can reason, a method on a trait is abstract override if and only if it calls super, but it breaks encapsulation to expect the client of the code to inspect the implementation of the method to know it needs a concrete implementation. Therefore, you must mark it abstract override to fully define the interface.