feat: domain finished

domain/loan/interface.go

@@ -0,0 +1,12 @@
+package loan
+
+import (
+	"github.com/eminetto/clean-architecture-go-v2/domain/entity/book"
+	"github.com/eminetto/clean-architecture-go-v2/domain/entity/user"
+)
+
+//UseCase use case interface
+type UseCase interface {
+	Borrow(u *user.User, b *book.Book) error
+	Return(b *book.Book) error
+}