try to set values. Let's try making such a function

Example3e.scala

def polySetAllBeansTo[A](beanList: List[ScalaBean[A]], initBean: ScalaBean[A]): Unit =
  beanList.foreach{bean =>
    bean.setTheA(initBean.getTheA)
  }

polySetAllBeansTo(beanList3, bean1)
// everything is now set to bean1's value

println(beanList2.map(_.getTheA))
polySetAllBeansTo(beanList2, bean1)
// ❌ Found:    (Playground.beanList2 : List[Playground.ScalaBean[?]])
//    Required: List[Playground.ScalaBean[Int]]
println(beanList2.map(_.getTheA))