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Playframework 는 Java코드로도 활용이 가능하지만 , Akka와 더불어

함수형언어의 특징을 살리고 일관성을 유지하기위해 Scala를 사용하는것이 추천되며

여기서는 스칼라의 몇가지 특징을 살펴보겠습니다.

원본 : https://docs.scala-lang.org/tour/tour-of-scala.html

//class Foo[+A] // A covariant class
//class Bar[-A] // A contravariant class
//class Baz[A]  // An invariant class


println("# Covariance")
abstract class Animal {
  def name: String
}
case class Cat(name: String) extends Animal
case class Dog(name: String) extends Animal

def printAnimalNames(animals: List[Animal]): Unit = {
  println("##" + animals )
  animals.foreach { animal =>
    println(animal.name)
  }
}

val cats: List[Cat] = List(Cat("Whiskers"), Cat("Tom"))
val dogs: List[Dog] = List(Dog("Fido"), Dog("Rex"))

printAnimalNames(cats)
printAnimalNames(dogs)


println("# Contravariance")

abstract class Printer[-A] {
  def print(value: A): Unit
}

class AnimalPrinter extends Printer[Animal] {
  def print(animal: Animal): Unit =
    println("The animal's name is: " + animal.name)
}

class CatPrinter extends Printer[Cat] {
  def print(cat: Cat): Unit =
    println("The cat's name is: " + cat.name)
}

val myCat: Cat = Cat("Boots")

def printMyCat(printer: Printer[Cat]): Unit = {
  printer.print(myCat)
}

val catPrinter: Printer[Cat] = new CatPrinter
val animalPrinter: Printer[Animal] = new AnimalPrinter

printMyCat(catPrinter)
printMyCat(animalPrinter)

println("# Invariance")

abstract class SmallAnimal extends Animal
case class Mouse(name: String) extends SmallAnimal
var smallAni:SmallAnimal = new Mouse("miky")

println(smallAni.name)



//val cat: Cat = catContainer.getValue // Oops, we'd end up with a Dog assigned to a Cat

abstract class Animal {
 def name: String
}

abstract class Pet extends Animal {}

class Cat extends Pet {
  override def name: String = "Cat"
}

class Dog extends Pet {
  override def name: String = "Dog"
}

class Lion extends Animal {
  override def name: String = "Lion"
}

class PetContainer[P <: Pet](p: P) {
  def pet: P = p
}

val dogContainer = new PetContainer[Dog](new Dog)
val catContainer = new PetContainer[Cat](new Cat)


// this would not compile
val lionContainer = new PetContainer[Lion](new Lion)