I had the same doubt. Where or how could this be useful? Would anyone here know how to give a tip? ...

# announcements

[Danilo Lima]

I had the same doubt. Where or how could this be useful?
Would anyone here know how to give a tip?

This is the tweet: https://twitter.com/pablisc0/status/1374468084916908041

[Javier]

cc @pablisco

[ephemient]

class Internal internal constructor() {
    ...
}

prevents external users from directly calling the constructor, allowing you to control access better (through a builder or factory method, perhaps)
this does the same thing for object

[Danilo Lima]

@ephemient Nice!

[pablisco]

Yeah, as @ephemient mentions it similar to having an internal constructor. This pattern is more useful if you have an object, as you can’t have a constructor, or if you have a data class, since the pesky copy function opens up the option to instantiate stuff.

This is a bit simplified, but in our case we had a situation where we had something like this:

sealed class PermissionResult {
  object Granted : PermissionResult()
  object Denied : PermissionResult()
}

And we get this from a suspend function in the same module:

suspend fun checkPermission() : PermissionResult

We wanted to create a function else where that can only be called if we have Granted as a value:

fun doSomethingFun(granted: PermissionResult.Granted)

This doesn’t work as is since anyone can reference Granted so by using internal implementations like this:

sealed class PermissionResult {
  sealed class Granted : PermissionResult() {
    internal object Internal : Granted()
  }
  sealed class Denied : PermissionResult() {
    internal object Internal : Denied()
  }
}

Means that you are forced to call the checkPermission function before you can call doSomethingFun which means it’s air tight and there is no way to forget to check the permission 🙂

[pablisco]

there is no way to forget to check the permission
*It’s a lot harder

[Danilo Lima]

@pablisco Great approach!

[pablisco]

Btw, I think I got the idea from the stdlib source code, but I can’t remember where now 😅