language tour: remove unnecessary object wrappers

Author: SethTisue

_tour/variances.md

@@ -37,20 +37,19 @@ Both `Cat` and `Dog` are subtypes of `Animal`. The Scala standard library has a
 In the following example, the method `printAnimalNames` will accept a list of animals as an argument and print their names each on a new line. If `List[A]` were not covariant, the last two method calls would not compile, which would severely limit the usefulness of the `printAnimalNames` method.
 
 ```tut
-object CovarianceTest extends App {
-  def printAnimalNames(animals: List[Animal]): Unit =
-    animals.foreach {
-      animal => println(animal.name)
-    }
-}
+def printAnimalNames(animals: List[Animal]): Unit =
+  animals.foreach {
+    animal => println(animal.name)
+  }
+
 val cats: List[Cat] = List(Cat("Whiskers"), Cat("Tom"))
 val dogs: List[Dog] = List(Dog("Fido"), Dog("Rex"))
 
 // prints: Whiskers, Tom
-CovarianceTest.printAnimalNames(cats)
+printAnimalNames(cats)
 
 // prints: Fido, Rex
-CovarianceTest.printAnimalNames(dogs)
+printAnimalNames(dogs)
 ```
 
 ### Contravariance
@@ -82,16 +81,14 @@ class CatPrinter extends Printer[Cat] {
 If a `Printer[Cat]` knows how to print any `Cat` to the console, and a `Printer[Animal]` knows how to print any `Animal` to the console, it makes sense that a `Printer[Animal]` would also know how to print any `Cat`. The inverse relationship does not apply, because a `Printer[Cat]` does not know how to print any `Animal` to the console. Therefore, we should be able to substitute a `Printer[Animal]` for a `Printer[Cat]`, if we wish, and making `Printer[A]` contravariant allows us to do exactly that.
 
 ```tut
-object ContravarianceTest extends App {
-  def printMyCat(printer: Printer[Cat], cat: Cat): Unit = {
-    printer.print(cat)
-  }
-}
+def printMyCat(printer: Printer[Cat], cat: Cat): Unit =
+  printer.print(cat)
+
 val catPrinter: Printer[Cat] = new CatPrinter
 val animalPrinter: Printer[Animal] = new AnimalPrinter
 
-ContravarianceTest.printMyCat(catPrinter, Cat("Boots"))
-ContravarianceTest.printMyCat(animalPrinter, Cat("Boots"))
+printMyCat(catPrinter, Cat("Boots"))
+printMyCat(animalPrinter, Cat("Boots"))
 ```
 
 The output of this program will be: