scala variance and bounds

scala variance and bounds

1. List[+T] is convariant 
2. def ::(elem child):List[me]                    ----> List[child] < List[me)
3. def ::[parent >: me](x: parent):List[parent]   ----> parent::List[me] returns List[parent]

scala> class parent
defined class parent

scala> class me extends parent
defined class me

scala> class child extends me
defined class child

scala> val xs = List(new me)
xs: List[me] = List(me@2b64976a)

scala> val c= new child
c: child = child@71b653af

scala> val p = new parent
p: parent = parent@6e782d03

scala> c::xs
res45: List[me] = List(child@71b653af, me@2b64976a)

scala> p::xs
res46: List[parent] = List(parent@6e782d03, me@2b64976a)