gistfile1.txt

Welcome to Scala version 2.8.0.r0-b20090301210344 (Java HotSpot(TM) Client VM, Java 1.6.0_10).
Type in expressions to have them evaluated.
Type :help for more information.

scala> trait ReponseHelper[A];  
defined trait ReponseHelper                            ^

scala> def doSomething[A](x : ReponseHelper[_ <: A]) : A = null.asInstanceOf[A] 
doSomething: [A](ReponseHelper[_ <: A])A                       ^

scala> val testHelper = new ReponseHelper[Int] {} 
testHelper: java.lang.Object with ReponseHelper[Int] = $anon$1@170119f

scala> doSomething(testHelper)
<console>:8: error: type mismatch;
 found   : java.lang.Object with ReponseHelper[Int]
 required: ReponseHelper[_ <: ?]
       doSomething(testHelper)
                   ^
scala> val testHelper2 : ReponseHelper[Int] = new ReponseHelper[Int] {} 
testHelper2: ReponseHelper[Int] = $anon$1@1298826

scala> doSomething(testHelper2)                                         
<console>:8: error: type mismatch;
 found   : ReponseHelper[Int]
 required: ReponseHelper[_ <: ?]
       doSomething(testHelper2)
                   ^

scala>  def doSomething(x : Int) = x
doSomething: (Int)Int

scala> doSomething(testHelper2)     
<console>:8: error: type mismatch;
 found   : ReponseHelper[Int]
 required: Int
       doSomething(testHelper2)
                   ^

scala> doSomething(testHelper) 
<console>:8: error: type mismatch;
 found   : java.lang.Object with ReponseHelper[Int]
 required: Int
       doSomething(testHelper)
                   ^