Extract element of given subclass from list of superclass - scala

Question

Given this code
class Animal{}
class Dog extends Animal{}
class Cat extends Animal{}
class Pitbull extends Dog{}
object MyClass {
def main(args: Array[String]) {
val animals: List[Animal] = List(new Dog(), new Cat(), new Pitbull(), new Dog(), new Cat())
getElementOftype(animals, PitBull)
}
def getElementOftype(list: List[Animal], givenType: ???): Animal = {
}
}
I want to extract the first element of type Pitbull from this List, How should I proceed with this?
What I tried but feels wrong
trait Identity{
def who: String
}
class Animal extends Identity{
override def who = "Animal"
}
class Dog extends Animal with Identity{
override def who = "Dog"
}
class Cat extends Animal with Identity{
override def who = "Cat"
}
class Pitbull extends Dog with Identity{
override def who = "Pitbull"
}
object MyClass {
def main(args: Array[String]) {
val animals: List[Animal] = List(new Dog(), new Cat(), new Pitbull(), new Dog(), new Cat())
println(getElementOftype(animals, new Pitbull()))
}
def getElementOftype(list: List[Animal], givenType: Animal): Option[Animal] = {
list.collectFirst{case s if s.who == givenType.who => s}
}
}
I want to simply pass Pitbull as a parameter instead of instantiating an empty object.
This one works but I don't think it's the best approach.
There must be a more scalaesque way to do this.

Answer 1

You can do something like this (not tested, there may be some typos):
def getElementOftype[A <: Animal](list: List[Animal])(implicit ct: ClassTag[A]): Option[A] = {
list.collectFirst { case s: A => s }
}
The ClassTag is necessary to be able to match on the A type in collectFirst.

Answer 2

when you write Animal extends Identity you mean Animal IS an Identity, which is wrong, using this approach is preferred:
class Animal { self: Identity =>
}
which means whenever you want to instantiate an Animal, you need to give an Identity to it, but why would you want to do that?
You can simply use pattern matching to filter required type like this:
import scala.reflect.ClassTag
def getElementsOfType[A <: Animal : ClassTag](animals: List[Animal]): Option[A] = {
animals.filter {
case a: A => true
case _ => false
}.map(_.asInstanceOf[A]).headOption
}
headOption is because your api returns Option[A] as result, you can make it return List[A] and get rid of the headOption in case you have multiple Pitbull's inside the list :)