Obviously you don't _always_ build an interface. That's how you end up with HelloWorldWidgetFactoryImplementationDataObject. The real question _should_ be: "At

Obviously you don't _always_ build an interface. That's how you end up with HelloWorldWidgetFactoryImplementationDataObject. The real question _should_ be: "At what point do you make an interface between function calls, given varying probabilities that there will be one or more implementations"