KotlinNativeTest

Wee sandbox for playing with Kotlin/Native

Notes

Setup

Tutorial for setting up a Multiplatform project: https://kotlinlang.org/docs/tutorials/native/mpp-ios-android.html

From that, there are a couple places you have to manually add folders if you're using Android Studio (particularly when creating the SharedCode folder at the same level as the app folder, then adding subfolders to it), but otherwise it's now fairly simple to get set up.

Usage

• Make sure to use List<T> instead of Array<T> in Kotlin if you want things to be [T] in Swift - otherwise the type doesn't get converted properly.

• Enum Classes are NOT imported as enums, but as some kind of class which you can't subclass. You can't have an exhaustive switch without a default case the way you can with Swift enums, but you can still switch using pattern matching:

  func printForDay(_ day: DayOfWeek) {
      switch day {
      case .monday:
          print("You can fall apart")
      case .tuesday,
           .wednesday:
          print("Break my heart")
      case .thursday:
          print("Doesn't even start")
      case .friday:
          print("I'm in love")
      case .saturday:
          print("Wait")
      case .sunday:
          print("Always comes too late")
      default:
          fatalError("Not a day")
      }
  }

  If you attempt to create a sublcass, you sort of can, but will get this warning when trying to create an initializer:

  Cannot override 'init' which has been marked unavailable

  I'm not entirely sure why this is, but it does seem like it's related to the fact that the Konan compiler generates Obj-C code rather than Swift code, and Obj-C doesn't play as nicely with enums as Swift.

• Sealed Classes are also imported as a non-enum class. You get the same error if you try to override them as you do with Enum Classes. You can still switch on the class type with pattern matching, but again, you will need to add a default case for the switch case to be considered exhaustive:

  func printHoursType(_ hours: HoursOfOperation) {
      switch hours {
      case is HoursOfOperation.Always:
          print("Always")
      case is HoursOfOperation.Variable:
          print("Variable")
      case is HoursOfOperation.Weekdays:
          print("Weekdays")
      case is HoursOfOperation.Weekends:
          print("Weekends")
      default:
          fatalError("Not a recognized subclass")
      }
  }

• From Swift, companion objects can be accessed in a manner similar to accessing them in Java - you must instantiate an instance of the companion object then call the companion methods on it:

  let dow = DayOfWeek.Companion().weekendDays

• Additionally, free functions in a given file can also be accessed in a manner similar to accessing them in Java, by using FileNameKt like a class name and calling it like a static instance member:

  CommonKt.createMessage()

• Once you've got it all set up, moving things from one folder to another is a total pain in the ass. You have to re-run the entire command to build the framework from scratch, and you have to nuke some combination of a) Derived Data and b) The build folder for your shared K/N project.