DI using cake

cake_di.scala

// from: http://jonasboner.com/2008/10/06/real-world-scala-dependency-injection-di

// (1).

case class User(username: String, password: String)

trait UserRepositoryComponent {
  val userRepository: UserRepository

  class UserRepository {
    def create(user: User): Unit = println(s"create $user")
  }
}

trait UserServiceComponent {
  self: UserRepositoryComponent =>
  val userService: UserService
  class UserService {
    def create(username: String, password: String): Unit =
      userRepository.create(User(username, password))
  }
}

object ComponentRegistry extends UserServiceComponent with UserRepositoryComponent {
  val userRepository = new UserRepository
  val userService = new UserService
}

// (2). same as (1) but separating interface from implementation

case class User(username: String, password: String)

trait UserRepositoryComponent {
  val userRepository: UserRepository
  trait UserRepository {
    def create(user: User): Unit
  }
}

trait UserRepositoryComponentImpl extends UserRepositoryComponent {
  override val userRepository: UserRepository = new UserRepositoryImpl
  private class UserRepositoryImpl extends UserRepository {
    override def create(user: User) = println(s"create $user")
  }
}

trait UserServiceComponent {
  val userService: UserService
  trait UserService {
    def create(username: String, password: String): Unit
  }
}

trait UserServiceComponentImpl extends UserServiceComponent {
  self: UserRepositoryComponent =>
    override val userService: UserService = new UserServiceImpl
    private class UserServiceImpl extends UserService {
      override def create(username: String, password: String) =
        userRepository.create(User(username, password))
    }
}

trait ComponentRegistry extends UserServiceComponent with UserRepositoryComponent

trait ComponentRegistryImpl extends ComponentRegistry with UserServiceComponentImpl with UserRepositoryComponentImpl

// (3). di using partial application & currying

case class User(username: String, password: String)

trait UserRepository {
  def create(user: User): Unit
}

trait UserService {
  def create: UserRepository => User => Unit =
    repo => user => repo.create(user)  
}

object MyRepository extends UserRepository {
  def create(user: User) = println(s"create $user")
}

object MyService extends UserService {
  def create_c = create(MyRepository)
}