Dependency Injection in Scala without Cake Pattern

0-common.Module.scala

package com.acme

import com.typesafe.config.Config

trait Module {
  implicit def config: Config
}

1-persistence.PersistenceModule.scala

package com.acme

trait PersistenceModule extends Module {
  implicit lazy val postgreSQL = postgresql.Database.fromConfig
  implicit lazy val mongoDB    = mongo.Database.fromConfig
}

2-persistence.postgresql.Database.scala

package com.acme
package postgresql

class Database(serverAddr: SocketAddress, val discriminator: Option[String])(implicit config: Config) extends DDL {
   ...
}

object Database {
  def fromConfig(implicit config: Config): Database =
    new Database(config(ConfigKeys.ServerAddress), None)
}

3-web.controllers.Foo.scala

package com.acme

class Foo(
  implicit postgreSQL: postgresql.Database, mongoDB: mongo.Database, config: Config
) extends Controller with Logging {
  ...
}

4-web.Global.scala

object Global extends GlobalSettings with PersistenceModule with Logging {
  override implicit def config: Config = Play.current.configuration.underlying

  lazy val foo = new Foo
  lazy val bar = new Bar

  override def getControllerInstance[A](clazz: Class[A]): A = {

    def bind[T](value: T)(implicit ct: ClassTag[T]): Option[A] =
      if (clazz == ct.runtimeClass) Some(value.asInstanceOf[A]) else None

    val instance =
      bind(foo) orElse
      bind(bar)

    instance.getOrElse(sys.error("Unable to instantiate controller of type: $clazz"))
  }
}

5-tools.InitializePlatform.scala

object InitializePlatform extends App with PersistenceModule {
  override implicit val config = ConfigFactory.load

  postgreSQL.init
  mongoDB.init
}