theodoreLee

class Contravariance[-T]
//defined class Contravariance


val contAny:Contravariance[Any] = new Contravariance[String]
/*
<console>:8: error: type mismatch;
 found   : Contravariance[String]
 required: Contravariance[Any]
       val contAny:Contravariance[Any] = new Contravariance[String]

theodoreLee

class Covariance[+T]

val coAny:Covariance[Any] = new Covariance[String] 
// coAny: Covariance[Any] = Covariance@33a626ac

val coString:Covariance[String] = new Covariance[Any]
/*<console>:8: error: type mismatch;
 found   : Covariance[Any]
 required: Covariance[String]
       val coString:Covariance[String] = new Covariance[Any]

theodoreLee

def bbb:Future[List[String]] = future { List("hi","there") }

def failedFuture:[List[String]] = future{ throw new RuntimeException("~~") } // or Future.failed(throw new ~~())

def action1 = Action {
  Async{
    bbb map {
      list => //list:List[String]
        Ok(list.mkString("~ "))
    }