added lesson 7

src/Lesson7/Variance.sc

@@ -0,0 +1,25 @@
+class Animal(val name: String, val kind: String)
+class Cat(name: String) extends Animal(name, "Cat")
+class Dog(name: String) extends Animal(name, "Dog")
+
+val anim1: Animal = new Animal("Booboo", "Baboon")
+val cat1 = new Cat("Miaou")
+
+// Standard polymorphism
+val anim2: Animal = cat1
+
+val dog1: Dog = new Dog("Choucroute")
+val anim3: Animal = dog1
+
+class Container[+A](val elems: List[A]) {
+  def get(i: Int): A = elems(i)
+  def put[B >: A](elem: B) = new Container(elem::elems)
+}
+
+val animalCollection = new Container[Animal](Nil).put(anim1)
+
+val catCollection = new Container[Cat](Nil).put(cat1).put(new Cat("Garfield"))
+
+animalCollection.put(cat1)
+
+val animalCollection2: Container[Animal] = catCollection