After updaing kotlin to 2.2 (probably), when building android release with gradle I'm gettinga million of

Info: Unexpected error while reading XYZ's kotlin.Metadata: element 'k' is missing.

Internet says to

-keep class kotlin.Metadata { *; }

, about which I'm unsure about I never had to mess with kotlin's default proguard keep rules Should I do it? Anyone else experiencing it?

Looking at some kotlin code and found a data class being declared, and inside of it there's a companion object that builds the data class. That seems smelly right. Does it actually break any "rule"... like "data classes are data classes, and not [blank]" is what i want to say. lol

Question: is there a way to mark an interface as "can only be implemented by a certain type and its subclasses"? Better yet, is there an alternate way to express the intent? I'm trying to wrap my hands around something like:

interface Extender<T> {
  context(thisValue: T)
  fun doSomething()
}

class Foo : Extender<Foo> {
  context(thisValue: Foo)
  override fun doSomething() { ... }
  
  // So, Foo would need a context-free overload of doSomething() anyways
  // passing itself as context, in order for outsiders to use it?
  fun doSomething() = context(this) { doSomething() }
}

Hey! Is there a native Kotlin function like dropWhile that doesn’t create a new list?

Hi. 👋 I'm trying to write a basic "Hello World" type app that can run on Android, iOS, Desktop, and Web. I am following this guide... https://www.jetbrains.com/help/kotlin-multiplatform-dev/quickstart.html Given that I'm developing on 🪟, I did the web KMP wizard which seemed to work well enough. Without much fuss, I have it running on Android and I next wanted to try Desktop but I ran into a problem. The tutorial suggests that there will be a composeApp [desktop] run configuration but I don't see that.

Hey folks. I need some help in diagnosing a test failure possibly related to design. Suppose I have this:

interface MyType

value class Wrapper(value: Int) : MyType, WrapperAddOp

interface WrapperAddOp : MyType {
  operator fun plus(rhs: Wrapper): Wrapper = // default implementation
}

When I try to run a test (JVM), I get a

NoSuchMethodError

when I try to invoke the

plus

method on

Wrapper

, saying that a mangled name starting with

plus

on

Wrapper

doesn't exist. Anyone with any insights on this?

Hey guys 👋 I'm trying context parameters, but failing in this case:

fun bar(
    lambda: context(String) () -> Unit
) {
    with("") {
        lambda()
    }
}

fun foo() {
    bar {
        this // error
    }
}

Am I missing something? Is this not supposed to give me a string? I am not able to get the context parameter of the lambda in any way. If I try

bar { str ->

then "str" here is also an error 🤔

Java's

CyclicBarrier

is really nice, but using it from Kotlin is not nice, since it's not coroutine-friendly. I've searched high and low, and haven't found a good alternative other than to roll my own. Has anyone run into this?

do kotlin data classes have no arg constructors? I'm asking because of gson documentation "If you are using ProGuard or R8 (for example for Android projects) you might not need any special Gson configuration anymore if your classes have a no-args constructor and use @SerializedName for their fields."

I used the AI Self-Review feature, and it gave me this:

The inner `None` object, used in the `Maybe` class to represent an absent value, is defined using `data object`. Although this is suitable for describing uniqueness and immutability, `data object` is over-specified here, as it incurs unnecessary memory allocation inefficiency compared to plain `object`. Consider replacing `data object None` with `object None`.

This seems like its wrong...

Hi everyone, I’m looking for an example of handling offline data. Specifically, I want to store data fetched from the network and display it in the UI. If it’s the first time, the app should fetch data from the network; otherwise, it should use the stored data. I’d also like to know the best way to handle data synchronization — for example, when a user saves new data while offline, it should automatically sync to the server once the network is available. This should work across android, iOS and desktop in a multiplatform setup.

I'm trying to make sense of the following error message:

Kotlin: Argument type mismatch: actual type is 'Select<CapturedType(out Record!)#1>', but 'Select<out CapturedType(out Record!)#2!>!' was expected.

This is triggered by the code:

val a: Select<out Record?> = TODO()
val b: Select<out Record?> = TODO()
a.unionAll(b)

where

Select

is declared in Java:

public interface Select<R extends Record>
extends
    ResultQuery<R>,
    TableLike<R>,
    FieldLike,
    FieldOrRowOrSelect
{

    @NotNull @CheckReturnValue
    @Support
    Select<R> unionAll(Select<? extends R> select);

}

Shouldn't

<? extends R>

allow

R

itself?

I just ran into an issue where I can't use a

value class

as a

vararg

parameter. Is there a reason for this? I don't understand why this would be a limitation.

Just completed the codelab from the official course to learn about View Models

It used the inbuilt (?)

ViewModel

library

Do I need to learn Hilt or Koin now before proceeding to make an app ?

I'm on a new project and it's insanely complex. I almost wish I can print out method names as they are called in order to help me see what methods are called on a button click for example. Is there any easy way to do that? So far I'm manually going in and doing multicursor search for

fun

and then putting a log statement. It works just takes a while.

I'm trying to fill Kotlin Developer Survey 2025 and I've got an error on the Kotlin Multiplatform page - there seems to be a required question/field I don't see and I can't proceed. Anyone else is having this problem?

Why can the type of an overridden property be changed to a subtype, but only if the property is a

val

, not a

var

?

sealed interface ParentType
class SubTypeA : ParentType
class SubTypeB : ParentType

sealed interface DataHolder1 {
  var data: ParentType

  // ERROR: Type of 'data' doesn't match the type of the overridden 'var' property 'var data: ParentType' defined in 'DataHolder1'.
  class HolderA(override var data: SubTypeA) : DataHolder1
  // ERROR: Type of 'data' doesn't match the type of the overridden 'var' property 'var data: ParentType' defined in 'DataHolder1'.
  class HolderB(override var data: SubTypeB) : DataHolder1
}

sealed interface DataHolder2 {
  val data: ParentType

  // but the type of `val` properties can be changed?
  class HolderA(override val data: SubTypeA) : DataHolder2
  class HolderB(override val data: SubTypeB) : DataHolder2
}

https://pl.kotl.in/esiw_FX5H

I'm trying to migrate from context-receivers to context-parameters and found this guide. https://blog.jetbrains.com/kotlin/2025/04/update-on-context-parameters/ I followed the guide for _Smooth Transition_ing, I replaced the freeCompilerArg

-Xcontext-receivers

with

-Xcontext-parameters

and resynced. I don't get to see the new inspection. Neither in the latest Android Studio stable/beta nor IntelliJ Ultimate. What am I missing?

IntelliJ IDEA 2025.2 (Ultimate Edition)
Build #IU-252.23892.409, built on August 1, 2025
Source revision: 0a9a69b3f9332

I'm having a small issue with functional/SAM interface, and I'm not sure if this is intended behavior, and if it is I don't understand why. If I convert this to an object extending

Example

and manually implement

example1

I can reference

example2

just fine, which puzzles me as to why the following snippet doesn't compile.

val example = Example {
	// this is without `example1`
	example2() // this line doesn't compile
}

fun interface Example {
	fun example1()

	fun example2() {
		println("Example")
	}
}

Hey everyone! I'm working on some code changes and have been getting an error re: the Kotlin Gradle Plugin. What is the appropriate channel to ask my question in? The specific error I've been getting when upgrading the language version from 1.9.25 to 2.2.0 is:

Caused by: java.lang.NoSuchMethodError: 'org.jetbrains.kotlin.buildtools.api.jvm.ClasspathEntrySnapshot org.jetbrains.kotlin.buildtools.api.CompilationService.calculateClasspathSnapshot(java.io.File, org.jetbrains.kotlin.buildtools.api.jvm.ClassSnapshotGranularity, boolean)'

Hi, I need some help 🙂 I'm working on a KMP project targeting Android and iOS, and I think the issue might be with my Kotlin code, so I hope someone can help me here. I'm having trouble signing out using Firebase Auth from GitLiveApp/firebase-kotlin-sdk. When I call onSignOutClicked in

ProfileScreen

, my app navigates to

AuthScreen

using the

signOut()

callback passed as a constructor argument to

ProfileScreen

. After that, my

AuthViewModel

collects

authService.currentUser

the same way it’s done in

ProfileViewModel

inside the

init

block. However, it still returns a non-null

FirebaseUser

, even though I already signed out. I’ll attach some code in a reply. Thanks in advance!

Hi. probably not the right channel but why are comments turned off on this video ?

Hello! Quick question regarding formatting in compose and IntelliJ. Is there a plugin/tool that formats the code in the editor (i.e. ⇧+alt+⌘ + L) and a CLI tool to ensure consistency?

can you define a context parameter for lambdas? something like

foo(f: context(users: UserService) Bar.() -> Unit)

Hey! I know Kotlin has lazy properties with its delegates feature. Is there any way to add lazy evaluation (or, equivalently for my use case, memoization) such that the first time I call

foo(arg)

,

foo(arg)

gets calculated, but the second, third etc. times that I call

foo

after that,

foo(arg)

just returns the already computed, stored value. E.g. in Python, this exists in the form of the

@Memoize

operator, if anyone is familiar with that. Is there any way to achieve this in Kotlin or should I just implement the memoization mechanism myself.

Is it possible to access an extension property given this setup?

fun main() {
    val book = Book("Kotlin Basics", List(10) { Page(it + 1) })
    
    val p = book.pages[4] // get the fullName from this scope given `book` and `p`?
}


class Book(val name: String, val pages: List<Page>) {
    val Page.fullName: String
        get() = "$name: Page $number of ${pages.size}"
}

class Page(val number: Int)

I suppose this is very niche..: Can I initialize class member `val`s from a lambda while also forbidding non-local returns in that lambda? • If I want to allow non-local returns, I can do this: playground example. Using the non-local return in this case actually triggers an error for kotlin 2 (not for 1.9.25), but for a different reason. It's easy to give an example where the non-local return is allowed also in kotlin 2. • marking the lambda

crossinline

, forbids the non-local return, but I can no longer initialize member `val`s from the lambda. I can initialize member `var`s, and local `val`s. See playground example here. I don't understand why initializing member

val

would no longer be possible. ◦ When trying to initialize a member

val

kotlin 1.9.25 errors "Captured values initialization is forbidden due to possible reassignment" (is the contract not understood here?) and kotlin 2 errors "Initialization of captured member values must be inlined" (is it not inlined?)

hey, we're seeing

Cannot invoke "java.util.Map.get(Object)" because the return value of foo() is null

very naively:

foo()

is a Kotlin function which returns

List<Bar>

, so under what conditions could it even return null?