Valentin Hinov

I think it's when people split layers into presentation, domain and data. The interface would go in a domain module while the implementation would go in a data module. Domain layer cannot depend on data layer, so it interacts with the interface in the business logic.

But....why. It just seems like creating class explosion for no reason other than to play tribute to a sense of clean code. Is just having the class without interface in your Data layer and using it directly wrong? What problem does it cause?

Yeah...clean...it works well for some projects... Because of that dependency arrow/onion architecture (business logic is the innermost layer and cannot not point/depend on an outer layer). If each layer is a different Grade module, this also avoids a circular dependency I guess?

Additionally helps in build time. When the data impl changes the ABI of the interface would not be changed. So the domain can avoid recompilation (compile avoidance) and all modules above it.