Simple dependency injection

ConstructorBasedDependencyInjection.scala

trait DatabaseLayer {
  def dependency: Int
}

trait ConcreteDatabaseLayer extends DatabaseLayer {
  def dependency: Int = 100
}

trait DatabaseResource1 {
  this: DatabaseLayer =>
  def resource1 = dependency * 10
}

trait DatabaseResource2 {
  this: DatabaseLayer =>
  def resource2 = dependency * 10
}

trait Service1 extends DatabaseResource1 {
  this: DatabaseLayer =>
}

trait Service2 extends DatabaseResource2 {
  this: DatabaseLayer =>
}

class Application extends ConcreteDatabaseLayer with Service1 with Service2

TraitBasedDependencyInjection.scala

trait DatabaseLayer {
  def dependency: Int
}

class ConcreteDatabaseLayer extends DatabaseLayer {
  def dependency: Int = 100
}

class DatabaseResource1(dbLayer: DatabaseLayer) {
  def resource1 = dbLayer.dependency * 10
}

class DatabaseResource2(dbLayer: DatabaseLayer) {
  def resource2 = dbLayer.dependency * 10
}

class Service1(resource1: DatabaseResource1)

class Service2(resource2: DatabaseResource2)

class Application(service1: Service1, service2: Service2)
val layer    = new ConcreteDatabaseLayer()
val service1 = new Service1(new DatabaseResource1(dbLayer)), 
val service2 = new Service2(new DatabaseResource2(dbLayer)))
val app      = new Application(nservice1, service2)