New.scala

DifferentTypes.scala

To write a method which takes two type parameters and both should not be the same:

   trait =!=[A,B]

    implicit def neq[A,B]: =!=[A,B] = null

    implicit def eqAmb[A]: =!=[A,A] = null
    implicit def eqAmbig2[A]: =!=[A,A] = null

    case class Foo2[A,B]( a: A, b: B )( implicit ev: A =!= B )
    //Foo2(1,2) compile error
    
    case class Foo3[A,B]( a: A, b: B )( implicit ev: A =!= B, ev2: String =!= B, ev3: A =!= String )
    //above is for none of the type parameter to be String. You need to do at both the places
    
    def notString[T](t : T)(implicit ev: T =!= String) = t
    
    
    http://stackoverflow.com/questions/6909053/enforce-type-difference/