Hey! What is an equivalent of Swift's failable initializer in Kotlin? Thanks! I have a Player and I want to init it with an asset, in case of not successful initialization I'd like player to be null, or at least throw.

Create a top-level function with the same name as your type (

Player

) that returns a

Player?

.

Failable initializers are definitely one of Swift’s, uh, “swift-ier” features lol - I would recommend maybe a

companion object

that defines

operator fun invoke(): Player?

or just a well-named factory method for this particular feature

thank you guys, I find them very useful in certain situations 🙂

more or less

the companion object approach is more appealing to me

I agree with the companion object approach. I like it so much that I've started tending towards things like this

interface Player  {
    val name: String
    val verification: Verification?

    val isVerified get() = verification != null

    companion object {
         operator fun invoke(name: String, verification: Verification? = null): Player {
             if (verification != null && verification.isNotValid)
                 throw IllegalArgumentException("Cannot create player with name $name because provided verification is not valid.")

             return object : Player {
                 override val name = name
                 override val verification = verification
             }
         }
    }
}

This cheeky construction has the full functionality of a class, but can still be implemented freely. You can even achieve "multiple-inheritance" using delegation:

class PlayerEntity(id: UUID, name: String, verification: Verification? = null) : Entity(id), Player by Player(name, verification)

The potential issue with that is that by not making it a data class, you lose the automatic implementation of

equals

,

hashcode

, and

copy

.

true, but you can't inherit from a data class anyhow 😮, so instead

PlayerEntity

can be the data class, if you fancy that. more to your point, with this approach, you can't override

equals

,

hashcode

, or

toString

at the interface level, so you'd want to have a basic implementation you always call in the event of multiple "constructors" (read: invoke), and add those

Any

functions there

Thanks for the extras Casey! I haven't see the notification for the follow ups.

@Hullaballoonatic interesting use of interfaces and invoke. I'm not surprised there's no performance impact. I believe the compiler will create an anonymous class definition for you, and since you use the same 'class' everytime, it's effectively like you defining a concrete implementation of the interface. At least that's my understanding of what will get produced for that scenario. Just JVM, and not Kotlin specific.