cake-pattern-example.scala

// simple example of the cake pattern

// abstract DAO trait
trait Repository[A, B]{
  // saves an entity, returns an ID
  def save(entity: A): B
  // more features..
}

trait RdbmsRepository extends Repository[MyUserCaseClass, Long]{
  
  def save(entity: MyCaseClass): Long = {
    //concrete implementation of save
  }
}

// service class, note the "self-type" at the top, signifying it "must have a repository mixed in"
trait UserService{
  this: Repository[MyUserCaseClass, Long] =>

  // by virtue of having a repository mixed in, the repository's functions become available 
  //without having to know which concrete implementation is mixed in at runtime.
  def addUser(user: MyUserCaseClass): Long = save(user)
}

// place to bootstrap dependencies
class Bootstrap{
  // using "with" to mixin the dependency. Can use a Fake/Mock trait during test
  val userService = UserService with RdbmsRepository

}