syntax struggle, I have an enum class, which I want to return an appropriate FragmentActivity subtype:

val activity:KClass<FragmentActivity>
   get() {
      return when (this) {
         Single, SingleWithSense, SingleWithPeriod, Dual, Echo -> AllocatedNodeActivity::class
         Central -> CentralNodeActivity::class
         Unknown -> PristineNodeActivity::class
      }
   }

It just yells at me because none of the return types match the KClass<FragmentActivity> type. What's the secret sauce I'm missing?

I’ve got a weird issue with, I think, the kotlin sdk version between intellij and maven. If I run my unit test from intellij (via the run configuration) it runs fine. If I run via maven (both from the command line and via the intelllij maven lifecycle actions) I get a complaint about, effectively, a smart-cast not working. In my pom.xml I have the kotlin version set to 1.3.72 and everywhere in project structure in intelllij seems to agree with that, but it looks like intellij’s is using another version. I would normally just ignore this, but if I try and change my code to not rely on the smart cast, intellij keeps warning me about “unnecessary cast” (and I have -werror enabled, so I can’t build with the warning). Where else can I check for a place where a version might be set incorrectly? I do know that the kotlinc plugin is 1.4.31, but I thought it should still be running “as” 1.3.71 if that’s set everywhere.

Any reason that UByte can do bitwise AND, OR, XOR, but not SHIFT operations?

This is my current code to match a command:

private fun extractCommand(command: String): Boolean {
    val asArr = command.split("\\s")
    if (asArr[0].equals(".attack", ignoreCase = true) && asArr.size == 3)
        return true
}

Is there a way to do this with regex? I think that's the best way

This message was deleted.

I'm getting this error even though my code compiles, I can even run my unit tests from the IDE. I'm using Android Studio 4.2 beta 6. I have another computer using the same version of AS and I don't get the error Any idea?

data class MyType(
    /**
     * Information [testing...]
     */
    val field: String,
)

I'm not sure if I have found a Kotlin bug or it's supposed to do this? But this data class results in a compiler error because of the

[testing...]

comment.

Parameter 'whatever' is never used

warnings for polymorphic methods, where in some cases, you really don't need to use the argument, but it's there for polymorphism. What's the idiomatic way to deal with this? I apparently cannot use `_`; I don't understand why.

I can set class

val

in

init

or in a constructor, but not both? What's the reasoning behind this code not compiling? https://pl.kotl.in/lVxY8idN4

Are there any known limitations to the visibility of extension functions on

operator

invoke? I’m having an issue where it’s only accessible within the same (gradle) module.

operator fun Foo.invoke(block: FooDsl.() -> Unit) { ... }
fun Bar.invoke(block: BarDsl.() -> Unit) { ... }

I.e. the following does not work from another module

foo { // cannot resolve
}

However, this does

bar.invoke {
}

There are no declarations of invoke in the classes in question. And for completeness this also works from another module

foo.invoke {
}

Is it correct that, currently, we can't create inline classes that implement Comparable<T>?

@elizarov This is a MCVE for the problem mentioned in my previous message. Calling next() on A from this code:

interface X<T> {
    operator fun plus(n: Int) : T
    fun next(): T = this + 1
}

inline class A(val value: Int) : X<A> {
    override operator fun plus(n: Int) = A(value + n)
}

causes

Exception in thread "main" java.lang.ClassCastException: class com.example.A cannot be cast to class java.lang.Number (com.example.A is in unnamed module of loader 'app'; java.lang.Number is in module java.base of loader 'bootstrap')
	at com.example.A.next-m5RZA0A(Example.kt:32)
	at com.example.ExampleKt.test(Example.kt:5)

This version causes the same exception:

interface X<T> {
    fun add(n: Int) : T
    fun next(): T = add(1)
}

inline class A(val value: Int) : X<A> {
    override fun add(n: Int) = A(value + n)
}

This version is OK:

interface X<T> {
    fun next(): T
}

inline class A(val value: Int) : X<A> {
    override fun next() =  A(value + 1)
}

This version is OK, too:

interface X<T> {
    fun next(): T
}

inline class A(val value: Int) : X<A> {
    operator fun plus(n: Int) = A(value + n)
    override fun next() =  this + 1
}

Does it have anything to do with boxing? Is this because the plus operator is called on a reference of an interface? Is this something limited to mathematical operators? What should I do? Should I prefer code generation instead of interface implementation when using inline classes?

Hi there! Does the following make sense? I'm totally new to Kotlin and just experimenting

fun <T> T?.onNull(effects: () -> Unit): T? {
    if (this == null) effects()
    return this
}

What I feel strange is that by defining the above extension, I'm allowed to invoke it on

non-nullable

types, which results a little counter-intuitive. I mean, given the above I can do:

val str: String = "helo"  // non-nullable type
str.onNull { print("Will never print as I'm not actually null") }  // <-- Why the compiler allows this?

Is it possible to restrict it just to nullables as in

T?

Thx 🙂

I noticed that two subtypes of a sealed class can be added to a Set with the same value. This is probably because Equals across different types will not return true. What would be the recommended approach to prevent same value, but different type of the same sealed class in a Set?

Can I match on pairs of when values? I have a

status

and a

newState

values, and I'd like to match on combinations. I could of course nest them, but I was hoping to match on a tuple like thing... e.g. when (status, newState) { 42, 13 -> "The answer is bad luck" }

Hi... I'm getting index out of bounds exception from this code. anyone know why?

private var worldSize: Int = 0
private var biomes: MutableMap<Biome, IntRange> = mutableMapOf()

data class PointData(val currentPoint: Int?, val currentBiome: Biome)

fun getPointData(point: Int): PointData {
    biomes.values.forEach {
        if (it.contains(point)) {
            return PointData(point, biomes.keys.elementAt(biomes.keys.indexOf(it)))
        }
    }
    return PointData(null, Savannah())
}

Exception in thread "main" java.lang.IndexOutOfBoundsException: Collection doesn't contain element at index -1.

🙋‍♂️ Hi guys, I'm new around here! A quick question, can I post my stackoverflow question link in here? Or should i just put the whole question here?

Hi, could somebody help me here? Asked in #coroutines but nobody still help.

Hi team! I understand what extension functions are, such as adding a newFunction

fun Bar.newFunction() {}

What exactly does this do?

fun Bar.() {}

Hi everyone, I have a state management challenge in our system and I'd love to hear how others might be solving this today, or to hear recommendations on how we could approach it. Our architecture is micro services based and we use mongodb for persistence. For examples sake, lets say there is an

AccountState

object in one micro service. Now for the various use cases that act on this state all have narrowed attributes of the state they're interested in. For example, Login only cares about Username and Password, whereas Change Profile Details cares about the Name and Address fields. When I retrieve data from mongo, I'd like to use a projection to only return the fields needed in the running use case and then I'd like to de-serialise that projection into something where my use cases can access those values without being cluttered with every filed that on the complete state object. ie. i don't want to create a version of the state where every value is nullable / wrapped in an Option. In typescript I would use something along these lines:

type State {
 const id: string
 const username: string
 const password: string
 const name: string
 const address: string[]
}

type NarrowViewOfState = Pick<State, "name", "address">

But as kotlin doesn't offer the same type flexibility; has anyone had success here?

Hello Q: Can we override the error messages from the FIR checker? In my case I have a private setter and would like to indicate to clients the supported way to update the value.

does anyone here know the answer?

This message was deleted.

How would I clear the console in Kotlin?

I am trying to use kotlinx serialization and I am working with the outlined basic example 3 in the kotlinx.serialization project. I am using Kotlin 1.4.31 and kotlinx.serialization 1.1.0. I am getting the attatched error even though I set up the test just like the example in the kotlinx.serialization code. Any thoughts on what I could be doing wrong? Or is this just a product of it still being in an experimental state.

I would like to use 

Kodein-DB

 in the multiplatform library, however because of the fact that it depends on 

serialization 1.1.0

 it forces me to upgrade kotlin version, because of this exception:

Your current Kotlin version is 1.4.21, while kotlinx.serialization core runtime 1.1.0 requires at least Kotlin 1.4.30-M1.

When I increase a version of Kotlin to 

1.4.30

 problem disappears and it’s not a problem to do so on library side, but when I’m building a new version of my lib including 

Kodein-DB

and trying to run the app that includes my library compiler forces me to also upgrade Kotlin version on the app side (because it’s also using

1.4.21

). Is there any possibility to overcome this problem? I wouldn’t like to force my clients to upgrade to Kotlin

1.4.30

It's for the runescape 2011 game, if anyone's interested =]

Hello! Does Kotlin supports top level delegates? If yes then how can i define operator fun getValue for that?

Why can't we just do:

class LootBox(item: Any) {
    private var loot = item
}

Instead of

class LootBox<T>(item: T) {
    private var loot: T = item
}