Coding example of "Variances" corrected

[andreamarconi]

The coding example inside the Variances (both in Covariance and Contravariance) wasn't completely working (as reported in #1533 ) , even if the proposed solution could be unelegant it should make possible for everyone to try it on their own platform.

[SethTisue]

is there someone watching this repo who could review this...?

[martijnhoekstra]

The original code works, but not in a REPL.

This is a rather roundabout way to make it work. Just remove the enclosing objects that extend App instead.

[martijnhoekstra]

Just eliminate the object instead of selecting from it

[martijnhoekstra]

Just eliminate the object instead of selecting from it

[SethTisue]

@andreamarconi interested in responding to the review feedback?

[andreamarconi]

@SethTisue no it's perfectly clear now, i tried the code without using a REPL and work perfectly

[SethTisue]

I've added some commits that get CI passing.

@martijnhoekstra I'm confused about where the actual fix is here. I must be missing something that's right in front of my face. wouldn't your suggestion just take us back to the original code?

[martijnhoekstra]

@SethTisue the issue is that this doesn't work in the repl, because extends App doesn't execute in the repl.

The easy fix is to remove the entire enclosing object, including the extends App. i.e. go from

object ContravarianceTest extends App {
  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)
}

to plain

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)

[SethTisue]

oh, I was confused, I thought this PR was the one to introduce the wrapper in the first place, but I see now that it wasn't

[SethTisue]

thank you Andrea and Martijn!