> There are surely cases where having an interface as an abstraction and multiple implementations makes sense.

I think most people aren't aware of the alternative, which is: A function that can call different implementations based on some other variable.

E.g. instead of having RealDB and MockDB type have a createUser() (method), you have a createUser() (function) that switches part of it's logic based on what DB is selected.

That's the prodecural way of achieving the same thing without needing a concept for virtual functions.

Casey explains this in the long discussion with Uncle Bob.