SOF question https://stackoverflow.com/q/50428367/1198559 - Version 2, Scala

SOF question https://stackoverflow.com/q/50428367/1198559 - Version 2

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object Rextester extends App {
    println("Hello, World!3")
 }

trait Dep[C]{
  type A
  type B
}

trait View1
trait View2

object Dep{

type Aux[C0, A0, B0]=  Dep[C0] {type A=A0; type B= B0}

implicit object DepInstanceView1  extends  Dep[View1] {
    type A=String
    type B=Int
  } 
  
  implicit object DepInstanceView2  extends  Dep[View2] {
    type A=String
    type B=Int
  } 
}

trait ServerSideFun[C]
{
   def f[A,B] (a:A)(implicit aux:Dep.Aux[C,A,B]):B
}

object ServerSideFun {
  implicit object View1Conv extends ServerSideFun[View1]{
    def f[A, B] (a:A)(implicit aux:Dep.Aux[View1,A,B]):B = 42
  }
  
  implicit object View2Conv extends ServerSideFun[View2]{
    def f[A, B] (a:A)(implicit aux:Dep.Aux[View2,A,B]):B = "42"
  }
}

object ServerSideFunAlternativeImplementation {
  implicit object View1Conv extends ServerSideFun[View1]{
    def f[A, B] (a:A)(implicit aux:Dep.Aux[View1,A,B]):B = 43
  }
  
  implicit object View2Conv extends ServerSideFun[View2]{
    def f[A, B] (a:A)(implicit aux:Dep.Aux[View2,A,B]):B = "43"
  }
  
}

[ + ] Show input
Compilation time: 0.73 sec, absolute service time: 0,74 sec

Error(s), warning(s):

source_file.scala:37: error: type mismatch;
 found   : Int(42)
 required: B
 Note: implicit object View2Conv is not applicable here because it comes after the application point and it lacks an explicit result type
    def f[A, B] (a:A)(implicit aux:Dep.Aux[View1,A,B]):B = 42
                                                           ^
source_file.scala:41: error: type mismatch;
 found   : String("42")
 required: B
    def f[A, B] (a:A)(implicit aux:Dep.Aux[View2,A,B]):B = "42"
                                                           ^
source_file.scala:49: error: type mismatch;
 found   : Int(43)
 required: B
 Note: implicit object View2Conv is not applicable here because it comes after the application point and it lacks an explicit result type
    def f[A, B] (a:A)(implicit aux:Dep.Aux[View1,A,B]):B = 43
                                                           ^
source_file.scala:53: error: type mismatch;
 found   : String("43")
 required: B
    def f[A, B] (a:A)(implicit aux:Dep.Aux[View2,A,B]):B = "43"
                                                           ^
four errors found