Where's the structural type?

gistfile1.scala

  object FuncConversions {
    //Nay
    implicit def guavaFunction2function[A, R](fn: (A) => R) = {
      new com.google.common.base.Function[A, R]{
        def apply(input: A): R = fn(input)
      }
    }
    
    //Yay
    class Func[A, B](fn: (A) => B) extends com.google.common.base.Function[A, B] {
      def apply(input: A): B = fn(input)
    }

    implicit def guavaFunction2function[A, B](fn: (A) => B) = new Func[A, B](fn)
  }