CovarianceContraVariance.scala

class Dog(name:String) extends Animal
// if DOG <:Animal does List[Dog] <: List[Animal]
val laika = new Dog("Laika")
val lassie = new Dog("lassie")
val hachi = new Dog("hachi")
val myDogs = List(lassie,hachi,laika)
val myAnimals: List[Animal] = List(lassie, hachi, laika)
class CovarList[+T]
val covarDogs:CovarList[Animal] = new CovarList[Dog]
class InvarList[T]
val invarAnimals:InvarList[Animal] = new InvarList[Animal]
val invarDogs:InvarList[Dog] = new InvarList[Dog]
class ContraList[-T] // -T <: Animal if we wanted to impose a type constraint Scala Type Bounds
val contraDogs:ContraList[Dog] = new ContraList[Animal]
//If your Generic Type Contains or Creates element of Type [T] it should be [+T]
//
//If your Generic Type Acts on or Consumes element of Type [T] it should be [-T]
//
//
//Covariant
//Cage , Garage , Factory , List
//
//ContraVariant
//Vet, Mechanic , Garbage pit , a Function
//Function can act on is applied on its arguments.