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?

I am following the course from google

I am running this code snippet:

import kotlinx.coroutines.*

fun main() {
    println("Weather forecast")
    delay(1000)
    println("Sunny")
}

But I am not seeing a delay between the two lines

How do I introduce delay between them ?

When asking Gemini why I couldn't access map keys with dot notation since they're so similar to objects, it told me that this notation is reserved for values that are known when the code is compiled. In contrast, subscript syntax is reserved for data that's only known as the program runs. Is this an accurate explanation?

In a similar vein of "why this not that," I'm not finding a compelling explanation for the differentiated uses of = and ->. Specifically in the contexts of single expression functions vs. lambdas. They're both predicates to their respective return statements, and as far as I can see, serve the same purpose. So why the distinction in form? Why not just use arrow syntax in both cases?

There is not kotlinx-html where all the SVG elements are present?

I'm looking for a text template engine, like Handlebars, but written in pure Kotlin multiplatform. The only one I've found is KorTE. Has anyone seen a handlebars or moustache implementation in kotlin?

hello i was recently search for how to publish Some KMP Packages to the community and how to index it in KLibs.io so i was wondering if any one can help

Just checking - in a when block like this:

import java.time.Period

fun Period.toDays() = when (this) {
  Period.ofYears(1) -> 365
  Period.ofMonths(1) -> 30
  else -> days
}

the check is an equality check, not an identity check, isn't it? I'm getting a compiler warning

Identity-sensitive operation on an instance of value type 'Period' may cause unexpected behavior or errors.

, but surely this is an equality check...

Is there a way to resolve the "Overload resolution ambiguity" without having dedicated function names?

fun <T : Any> foo(block: () -> T?) {}
fun <T : Any> foo(block: () -> List<T>?) {}
fun <K : Any, V : Any> foo(block: () -> Map<K, V>?) {}
fun <T : Any> foo(block: () -> Set<T>?) {}
foo { "foo" }
foo { listOf("foo") }
foo { mapOf("foo" to "bar") }
foo { setOf("foo") }

(And without casting the arguments, I mean that the right method is used automatically)

Shouldn't each of these pre-condition calls imply that

foo

is non-null? So why is the second

foo

call not working?

fun foo(foo: Any) = null
val foo: String? = null
foo(foo)
check(foo != null)
require(foo != null)
assert(foo != null)
foo(foo)

This message was deleted.

sealed interface RandomState {
    data object Empty: RandomState

    enum class Validity(val message: String): RandomState {
        Valid("Is valid"),
        Invalid("Is not valid"),
    }
}

fun foo(state: RandomState) {
    when(state) {
        RandomState.Empty -> Unit
        RandomState.Validity.Valid -> {
            showMessage(state.message)
        }
        RandomState.Validity.Invalid -> {
            showMessage(state.message)
        }
    }
}

Why is it not able to smart cast to

RandomState.Validity.Valid

and

RandomState.Validity.Invalid

?

fun foo(): String {
    var local: String? = null
    if (local == null) {
        local = "hello"
    }
    return local // compiler still thinks nullable
}

Why doesn't this smart cast?

Is there anyway to pass compiler flags for build.gradle.kts file? My use case requires context parameters which need to be enabled by a compiler flag.

hi all first day here what should i do?

I have an interface

Gateway

and a class parameter

KClass<Gateway>

. But when I pass an instance of

KClass<GatewayImpl>

, the compiler complains. Is there a way around this? Casting works, so something is correct.

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?