simple inejctor

injector.scala

import scala.reflect.{classTag, ClassTag}

object Injector {
  private val rootInjector =  new Injector(None)
  def createInjector =  rootInjector.createChild(rootInjector)
  def mapValue[T:ClassTag](instance:T): Unit =
    rootInjector.mapValue[T](instance)
}

class Injector(val parent:Option[Injector]) {
  private val valueMap =
    scala.collection.mutable.Map[ClassTag[_], Any]()

  def clear = valueMap.clear 
  def createChild:Injector = new Injector(Some(this))
  def createChild(parent:Injector):Injector = new Injector(Some(parent))

  private def hasInjectedValue(cTag:ClassTag[_]):Boolean = {
    valueMap.get(cTag) match {
      case Some(_) => true
      case None => false
    }
  }

  def mapValue[T:ClassTag](instance:T): Unit = {
    valueMap += classTag[T] -> instance
  }

  def getInstance[T:ClassTag]: T =
    valueMap.get(classTag[T]) match {
      case Some(i) => i.asInstanceOf[T]
      case None => {
        parent match {
          case Some(j) => j.getInstance[T]
          case None => throw new Error("no injected target error")
        }
      }
    }
}

trait Inject {
  var injector:Injector = Injector.createInjector
  def injected[T:ClassTag]: T = injector.getInstance[T]
}

trait CustomInject {
  val injector:Injector
  def injected[T:ClassTag]: T = injector.getInstance[T]
}


//How to use

class A(val x:Int)
class B

class C extends Inject {
  val a: A = injected[A]
  val b: B = injected[B]
  def run: Unit = println(a.x, b)
}

Injector.mapValue(new A(4))
Injector.mapValue(new B)
val c = new C
c.run

class D extends CustomInject {
  val injector = Injector.createInjector

  val a: A = injected[A]
  val b: B = injected[B]
  def run: Unit = println(a.x, b)
}

val d = new D
d.run