Hey, I have a timestamp like this

2025-09-02T10:59:38+02:00

and at one point (envelope) I deserialize it as

Instant

with no problem. At another point (payload) I want to do the same but it doesn't work. I looked at the imports but both import

kotlinx.datetime.Instant

. But one does so from

org.jetbrains.kotlinx:kotlinx-datetime

and the other from

org.jetbrains.kotlinx:kotlinx-datetime-jvm

, with the latter not working. The only dependency I have in both my

common

and

jvmBackend

modules is

org.jetbrains.kotlinx:kotlinx-datetime

so I guess it selects which one to use by itself. What would be the best course of action to remedy this Problem? Edit: Seems like I have to use

Instant.parse()

, before I had the json serializer do it, since most payloads are json and a select few are plain strings, but before I had no problems just using the json parser for that and it allowed me to have a more generic approach for all messages.

I'm trying to convert some of our existing Java classes to Kotlin using IntelliJ's built-in converter. Unfortunately, when I run the conversion I get the following error in the logs. I've already tried to reproduce the issue with a minimal setup, but so far without success. I'm hoping someone can, based on the error message, suggest where I should look next.

👉 I've noticed that several Kotlin code completions seem to be missing. I don’t have exact examples right now, but starting about 1–2 months ago some intention actions (the fixes that usually help improve code) stopped showing up. Has anyone else experienced this? 🤔

Today I learned this is valid. Does anyone have insight into why this is? To me, it seems extremely wrong and confusing to be able to assign a

val

at all somewhere other that its declaration site.

class Test {
    private val test: String
    
    init {
        test = "Hello"
    }
}

Hi all. I want to use my immutable kotlin data class in tests in my java code. In tests I initialize my data class with different values. In java I cannot use default parameters of the copy method. Also it seems to me too expensive to create multiple copies of the object while initializing it: each modification produces a new value. Ideally, I would like to use a builder to generate the object I need. Are there any tools to automatically create such a builder from an immutable data class or do I have to write it myself? edit: essentially to generate a "mutable" version of my data class.

huh, with kotlin 2.2.20, https://github.com/josephlbarnett/leakycauldron/blob/fe5e5514dd035c9e0eaae70c6fdb422170035cf1/graphql/src/main/kotlin/com/trib3/graphql/execution/LeakyCauldronHooks.kt#L49-L50 gives this warning:

[WARNING] file:///home/jbarnett/workspace/tribe/leakycauldron/graphql/src/main/kotlin/com/trib3/graphql/execution/LeakyCauldronHooks.kt:50:30 This declaration overrides a deprecated member but is not marked as deprecated itself. Add the '@Deprecated' annotation or suppress the diagnostic.

... but gives no such warning in 2.2.10 (I mostly only care because

-Werror

). it looks like it is marked deprecated itself unless I'm missing something? I can, of course, override the non-deprecated methods instead but wanted to understand what's going on.

If

this.getChildAt(0)

returns

View!

should it always be guarded with an

if

like this?

if (childCount > 0) {
    getChildAt(0) as? AndroidComposeView
}

Why can’t I just do

getChildAt(0) as? AndroidComposeView

for an

AndroidComposeView?

that is

null

if the

View!

was null?

Is there a quick introductory writeup on Kotlin compiler extensions? It’d be great if the article covered what they can and can’t do, the general structure of them, and such. I want to know if you can use an extension to add new syntax, or all code has to use valid existing syntax whether it’s processed by the extension later or not, how much the input code can be altered by the extension, and so on

Hi All, if I have a Map<String, String>, is there a way to automatically create a data class with fields like Int, Double, Boolean. (At the moment I have to create tons of code with very basic conversions.)

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Is there a way for me to clear caches for only one Kotlin file? Sometimes the IDE plugin goes crazy, and I have to do a full Invalidate+Restart, but I wish I could do it only for the file it's freaking out on

Is there any YouTrack issue to make the compiler allow the following, or is there a reason it can't?

fun foo(n: Int): Int {
    require(n >= 1 && n <= 3)
    return when (n) {
        1 -> 10
        2 -> 20
        3 -> 30
    }
}

Is it possible to suppress deprecation warnings without doing it for the entire file? When I try to suppress a usage in a top-level function, it says "redundant suppression" and the import statement still has the deprecation warning.

import com.whatever.DeprecatedClass <-- Deprecation warning persists

@Suppress("deprecation") <--- redundant suppression
fun test(value: DeprecatedClass) { ... }

I'm working on a library (an android library to be exact). if I update that lib to kotlin 2.2.20, would all of my consumers be forced to use that new version? like. is it better for me to use an old version?

Hi everyone! This is Sudarshan. I’m reaching out to share a serious problem I’m facing. I belong to a community of students where most people are only familiar with Java, JavaScript, Python, C, and C++. It’s really hard to find someone who knows Kotlin. In fact, I was talking with one of my professors at college, and when she saw Kotlin mentioned in my resume, she said she had never heard of it before. Well, it’s not rare to find someone in tech who doesn’t know about Kotlin—but I want to change that. To make a difference, I’ve decided to approach different colleges in my city and give talks on Kotlin and Kotlin Multiplatform. I believe that spreading awareness about Kotlin will help increase its adoption and possibly make it even more popular than Java. I’m not sure if this is the right place to talk about it, but am I thinking in the right direction?

Hey team, I was reading a few articles about Compose and View interoperability, and some people mentioned benchmarking to identify performance differences when using Compose within existing View-based screens. I haven’t done any benchmarking before, so I wanted to ask — what specific areas are usually measured in such cases? For example: • Rendering or layout inflation time • Frame rendering and jank rates • Recomposition or invalidation overhead • Memory and CPU usage differences Are there any other key metrics we should look at to pinpoint performance issues more accurately? Also, if you know any good learning resources, tools, or examples to understand how to write or run these benchmarks (especially for Compose), I’d really appreciate your suggestions. Thanks! 🙏

is there a way to make a constructor private and instead provide a constructor function? I need to capture a reified type

inline fun <reified T : Any> createEvent(
    endpointTarget: String,
    id: String,
    type: String,
    payload: T,
) = Event(
    endpointTarget = endpointTarget,
    id = id,
    type = type,
    payload = payload,
    typeInfo = typeInfo<T>()
)

class Event<out T : Any> private constructor(
    val endpointTarget: String,
    val id: String,
    val type: String,
    val payload: T,
    val typeInfo: TypeInfo,
)

can anyone recommend something to generate code from openapi definitions? using the official openapi generator generates code that won't compile

If I have something like this:

class Foo {
    var number: Int = 0
}

Is it possible to pass a reference to the

number

property to another class so that the other class can reassign it?

I want to create a function that is

inline fun <reified T> foo(): T

. This function calls a function

fun <T> impl(type: KType): T?

. I want the behavior that: • If

foo

is called with a nullable type (e.g.

foo<Int?>()

), then nulls can be returned. • If

foo

is called with a non-nullable type (e.g.

foo<Int>()

), if

impl()

returns

null

then it throws an NPE. Is this possible? Usually I would use overloads when I have two functions that only differ from the nullability of their parameters/receivers, but I don't think this is possible when they only differ by return type?

For something like https://github.com/material-foundation/material-color-utilities/blob/main/kotlin/hct/Hct.kt#L158 which accepts a color as

Int

, passing in the encoded ARGB channels, is there a more "pleasant" way of replacing

Hct.fromInt(0xFFFF0000u.toInt())

with something closer to how it is in Java

Hct.fromInt(0xFFFF0000)

the trailing

u.toInt()

is just noise when I read this call. The only thing I can think of is adding my own

fun Hct.fromLong

extension to make it read better in Kotlin.

Hi! I'm trying to use contracts but I don't entirely get it. My problem is I want to have the return value of a member function on a data class help the compiler infer something about a value of that data class, and I don't understand if this is actually doable with contracts or not. Here's a minimal example:

data class TimeRange(
  val from: Instant,
  val to: Instant?,
) {
  fun isOpenEnded(): Boolean {
    return this.to == null
  }
}

Optimally, I'd like to be able to use this helper and have the compiler still correctly infer whether

to

is null or not. If I now add a method to check if a TimeRange ends later than another, it might look like this (it's logically incorrect but nevermind that for the sake of the example)

fun endsLaterThan(other: Timerange): Boolean {
    return this.isOpenEnded() || (!other.isOpenEnded() && (this.to > other.to))
}

However, this code does not work as-is, the compiler gives me trouble about nullability. To my human eyes and brain it's clear that the final statement

(<http://this.to|this.to> > <http://other.to|other.to>)

is only reachable if neither

<http://this.to|this.to>

or

<http://other.to|other.to>

is

null

, since that would short circuit the boolean operations. The compiler does not infer this, so I thought I might be able to help it along using contracts! I have tried to add something like this, but it does not seem to work since I'm using

implies

to say something about a member of the receiver and not just the receiver itself?

fun isOpenEnded(): Boolean {
  contract {
    returns(true) implies this.to == null
    returns(false) implies this.to != null
  }

  return this.to == null
}

If there's a way to make this work, I'd love to know! Links to reading material about contracts in general is also appreciated 👍

I'm not too experienced, especially when it comes to string processing in Kotlin. So sorry if this is a stupid Noob question. Here is the behavior I get and what I'm not really understanding: I have a simple text with six words in three lines separated by commas:

Boo,Boo,Boo,Boo,Boo,Boo
Foo,Foo,Foo,Foo,Foo,Foo
Goo,Goo,Goo,Goo,Goo,Goo

This is my code together with the output I get as comments.

import java.io.File

fun main() {
    val chars: String = File(
        "C:\\Work\\Kotlin\\test\\src\\main\\resources\\MyTest.txt"
    ).readText(Charsets.UTF_8)
    val lines = chars.split("\n")
    println("Number of Lines: ${lines.size}") // Number of Lines: 3
    println(lines[0])                         // Boo,Boo,Boo,Boo,Boo,Boo
    println(lines[1])                         // Foo,Foo,Foo,Foo,Foo,Foo
    println(lines[2])                         // Goo,Goo,Goo,Goo,Goo,Goo
    val myList1 = lines[0].split(",")
    val myList2 = lines[1].split(",")
    val myList3 = lines[2].split(",")
    println("myList1: $myList1")                // ]
    println("Number of Words: ${myList1.size}") // Number of Words: 6
    println("myList2: $myList2")                // ]
    println("Number of Words: ${myList2.size}") // Number of Words: 6
    println("myList3: $myList3")                // myList3: [Goo, Goo, Goo, Goo, Goo, Goo]
    println("Number of Words: ${myList3.size}") // Number of Words: 6
}

As you can see it only outputs myList3 correctly. myList1 and myList2 just output ']'. But if you look at the size, it seems like it processed my string correctly. And the thing is, this depends on which line is the last in the txt file. It just outputs the last line the way I'd expect, but not the previous ones. Why is that? Is this a bug? JDK: corretto-23.0.2 Ide: IntelliJ IDEA 2025.1.5.1 (Community Edition) - Build #IC-251.28293.39, built on September 2, 2025

Would it be unreasonable as a language feature, to give compiler hints on required fields to be set in type-safe builders? Also promotion of type-safe builder relevant properties, in the editor?

Given the following example, can one explain why

when

is uncomplete? https://pl.kotl.in/uwOMcC-Fd

I find very interesting that this code isn't ambiguous.

import io.ktor.http.HttpStatusCode.*

@Serializable
private data class NotFound(val id: String)

val f = foo<NotFound>(NotFound)
            |         |
            |         HttpStatusCode.NotFound
            data class NotFound

I have

fun <T> foo1(vararg elements: Iterable<T>) = /* ... */

I also have

fun foo2(vararg elements: List<Bar>)

what exactly happens when I call

foo1(*elements)

from within

foo2

? what does the spread operator do here? is this zero cost?

I'm trying to convert a while(x.hasNextPart()) loop into a sequence; so far I've found generateSequence but I'd need to bundle up the hasNext boolean so I can stop, e.g.

generateSequence { Elem(it.hasNextPart())}.takeUntil {it.hasNext}

is there a better way to do that? and in that case, would you prefer an Iterator instead?

Dear all. Why does Kotlin force parameter variables to be constants,

val

? Kotlin does not have a concept of a "pointer to a const", therefore I can change the referenced value, unless it is immutable. I mean,

val

parameter variable does not amount to much unless the referenced value is immutable.