Scaldi

Lightweight Dependency Injection Library

Created by  Oleg Ilyenko  @easyangel

Only 3 Concepts

1  Injector

2  Module

• A place where you define the bindings
• DSL for bindings
• extends Injector

3  Injectable

inject [SomeClass]
        

inject [Database] (identified by 'remote and by default new Riak)
        

Injector  and  Injectable

class OfficialMessageService(implicit inj: Injector)
          extends MessageService with Injectable {

  val officialGreeting =
    inject [String] (identified by "greeting.official")

  def getGreetMessage(name: String) =
    s"$officialGreeting, $name!"
}
        

class UserModule extends Module {
  bind [MessageService] to new OfficialMessageService

  binding identifiedBy "greeting.official" to "Welcome"
}
        

★ Something Special ★

Injector Composition

def tokenModule = new Module {
  bind [Tokens] to new TokenRepo(db = inject [Database])
}

def dbModule = new Module {
  bind [Database] to new Riak
}

def appModule = tokenModule :: dbModule
        

def mocksModule = new Module {
  bind [Database] to new InMemoryDb
}

implicit val testModule = mocksModule :: appModule
        

Injector Types

• Mutable Injectors
• Immutable Injectors
• Properties Injector
• Play Configuration Injector
• Create you own, it's easy

trait Injector {
  def getBinding(identifiers: List[Identifier]): Option[Binding]
  def getBindings(identifiers: List[Identifier]): List[Binding]

  // ...
}
        

Generics

binding identifiedBy "intAdder" to
  ((a: Int, b: Int) => a + b)

binding identifiedBy "mapping" to Map(
  "scala" -> "http://scala-lang.org",
  "play" -> "http://www.playframework.com",
  "akka" -> "http://akka.io"
)
        

val intAdder = inject [(Int, Int) => Int]

val mapping = inject [Map[String, String]]
        

Conditions

class UserModule extends Module {
  bind [MessageService] when (inDevMode or inTestMode) to
    new SimpleMessageService

  bind [MessageService] when inProdMode to
    new OfficialMessageService
}
        

def inDevMode(implicit inj: Injector) = {
  val mode = inject [Mode]
  Condition(mode == Dev)
}
        

Binding Lifecycle

class MyModule extends Module {
  bind [ActorSystem] to
    ActorSystem("ScaldiExample") destroyWith (_.shutdown())

  bind [Database] to new Mongo initWith (_.start())
}
        

implicit val injector = new MyModule

// do stuff ...

injector.destroy()
        

Extensibility

• Extend almost any part of the library
  • Injector
  • Condition
  • Binding and BindingWithLifecycle
  • Identifier - create your own and define how they match
• Type classes
  • CanCompose - defines how Injectors can be composed together
  • CanBeIdentifier

Create  a  Controller

class Application(implicit inj: Injector)
          extends Controller with Injectable {

  val messageService = inject [MessageService]

  def index = Action {
    Ok(views.html.index(
      messageService.getGreetMessage("Test User")))
  }
}
        

Then  Bind  it

class MyModule extends Module {
  binding to new Application

  bind [MessageService] to new OfficialMessageService
}
        

Define  Global

object Global extends GlobalSettings with ScaldiSupport {
  def applicationModule =
          new MyModule :: new SomeOtherModule
}
        

Configure  routes

GET  /   @controllers.Application.index
        

Play  Extras

inject [Application]
inject [Mode]
inject [Configuration]
        

bind [Thing] when (inDevMode or inTestMode or inProdMode) to
  new SomeThing
        

inject [String] (identified by "db.host")
inject [Int] (identified by "db.port")
        

Akka  Injectable

• injectActorProps
• injectActorRef

class Receptionist(implicit inj: Injector)
    extends Actor with AkkaInjectable {

  val orderProcessorProps = injectActorProps [OrderProcessor]

  val priceCalculator = injectActorRef [PriceCalculator]

  def receive = {
    case PlaceOrder(userName, itemId, netAmount) =>
      val processor = context.actorOf(orderProcessorProps)
      // ...
  }
}
        

Actor Ref  Factory

• Should be implicitly available
  • ActorContext (within an actor)
  • ActorSystem (outside of actor)
• Creates and configures an actor
  • Setups correct actor hierarchy
• Integrates with Scaldi via Props

Actor  Bindings

class OrderModule extends Module {
  bind [ActorSystem] to ActorSystem("ScaldiExample")
    destroyWith (_.shutdown())

  binding toProvider new Receptionist
  binding toProvider new OrderProcessor
  binding toProvider new PriceCalculator
}
        

More Information

• Home page: http://scaldi.org
• GitHub: https://github.com/scaldi
• Blog: http://hacking-scala.org/
• StackOverflow: tag scaldi
• Typesafe activator templates
  • Scaldi Play Example
  • Scaldi Akka Example
• This presentation: http://scaldi.github.io/scaldi-presentation

EOF

Thank you!

Questions?