Generic lists in scala

Question

As I was working with Java I was able to create generic lists with constraints, covariant, Contravariant etc..

List<? extends Chat> chats=new ArrayList<Siamois>(); ...

But know I have to work in Scala I used constraints for methods and for class for instance :

def addToList[T <: Chat](t:T):List[T]=List[T](t)

but in fact is there a way to write these lines of java in Scala ?

 List<? extends Chat> chats=new ArrayList<Siamois>(); List<? super Siamois> siamois2=new ArrayList<Chat>();

thanks

Jasper-M · Accepted Answer · 2018-01-13 21:02:27Z

The literal translation would be

import java.util.{List, ArrayList} val chats: List[_ <: Chat] = new ArrayList[Siamois] val siamois2: List[_ >: Siamois] = new ArrayList[Chat]

But note that the immutable List from the Scala standard library is covariant by definition. In idiomatic Scala code you won't need use-site variance. You'll probably want to read up on Scala's declaration-site variance.

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