Hi developers, I would need one advice. I have collection of data ( 1000 instances of Car). I have one thread to change data and multiple threads to access data.. I need to access it by id, so MutableMap is selection. But I need also filter data out by range of lon, lat to calculate the closest few. What would be the fastest and the best approach? Currently I have (code bellow), but this searches through all elements.

fun nearCar(minLat: Float, maxLat: Float, minLon: Float, maxLon: Float): List<Car> {
    return mutableMapCars.values.parallelStream().filter {
        it.lat > minLat &&
                it.lat < maxLat &&
                it.lon > minLon &&
                it.lon < maxLon
    }.toList()
}

data class Car(
    val id : Long,
    val registration : String,
    val lon: Float,
    val lat: Float
)

I feel silly having to ask this but… what’s going on here?

Does anyone know if

bin/kotlinc

found in kotlin-native cli release tar can be used interchangeably with the one found in kotlin-compiler.zip?

Is there a kotlin common / multi platform logging library or is it just preferred to use platform specific ones?

hey! I'm using kotlin with coroutines with spring webflux and I'm having some issues regarding KContinuation when trying to use PreAuthorize

Is there any Plugin that will let me generate function that creates an instance of

data class

with its default values? For example I have:

data class User(
    val id: String,
    val deviceId: String
)

and plugin will generate:

fun userOf(
    id: String = "",
    deviceId: String = "",
): User =
    User(
        userId = userId,
        deviceId = deviceId,
    )

or something similar? (Sorry if wrong channel)

Hi folks. I am having a behavior in Kotlin that does not look right for me. So I have declared the following:

val title: (locale: Locale) -> String? = {
    getPrompt(it.language)
}

fun getPrompt(string: String) : String? {
    return if (string == "A") null
    else "A"
}

getPrompt

can return null, hence the

String?

However, the following check returns a warning from the compiler ("the comparation can be simplified since title is never null")

if (title == null) {

}

But title can effectively be null. Is this a bug on AS/JetBrains?

How can I create a sub-scope of a CoroutineScope? I'm looking for something like

val parentScope: CoroutineScope
val childScope = parentScope.something()

I want childScope to be cancelled if parentScope is, but for parentScope not to be cancelled if childScope is

This seems to be an interesting topic, https://stackoverflow.com/q/64385753/11377112 anybody giving it a shot?

I'm not sure of the best channel for this discussion, but it deals with delegates and how they are used to grab Property File values. I have seen it described very similarly before in an article that we can use a simple convention such as

val pluginGroup: String by project

This will search for .property files for the key

pluginGroup

and return it's value as a

String

. I am impressed by that, but how the heck does this magic work? This will only return

String

values, so even if we have the following in the .properties file...

platformDownloadSources = true

It will still only return

"true"

as a

String

. I am curious of how this mechanism works and why it is limited to only

String

and why it is limited to the specific name I have for the variable. Meaning I must name my variable the same as is in the .properties file.

I have this piece of code and I’m wondering if this is a bug or just not possible (as designed) for the type inference of Kotlin. Here is a snippet:

class MyList<T> {
    @JvmName("flatMapList")
    fun <R> flatMapList(block: Function1<T, List<R>>): MyList<R> = TODO()

    @JvmName("flatMapListPair")
    fun <R> flatMapList(block: Function1<T, Pair<R, R>>): MyList<R> = TODO()

    @JvmName("flatMapList2")
    fun <R> flatMapList2(block: (T) -> List<R>): MyList<R> = TODO()

    @JvmName("flatMapListPair2")
    fun <R> flatMapList2(block: (T) -> Pair<R, R>): MyList<R> = TODO()
}

fun test() {
    val x = { it: Int -> Pair("1", "2") }
    val y = { it: Int -> listOf("1", "2") }

    MyList<Int>().flatMapList(x) // OK
    MyList<Int>().flatMapList({ it: Int -> Pair(1, 2) }) // ERROR

    MyList<Int>().flatMapList2(x) // OK
    MyList<Int>().flatMapList2({ it: Int -> Pair(1, 2) }) // ERROR

    MyList<Int>().flatMapList(y) // OK
    MyList<Int>().flatMapList({ it: Int -> Pair(1, 2) }) // ERROR

    MyList<Int>().flatMapList2(y) // OK
    MyList<Int>().flatMapList2({ it: Int -> Pair(1, 2) }) // ERROR
}

Why does the compiler (and IDE) generate an error when directly assigning the lambda, but it compiles fine when using a temporary variable (

x

and

y

)?

I'm running into a concurrency issue I don't understand how to fix. I have a function in my repository called 

getTile

, which may need to call 

renewAccessToken

. If I make ten parallel calls to 

getTile

, and I need to renew the token, one call should do the renewing, and the rest should block until it is done. I'm wondering if I want something that emits a stream of (mostly-identical) access tokens, which getTile pulls the latest access token from. The stream then chooses whether to renew or present a stale value

Hi all!, I am having a bit of trouble setting up Kotlin multiplatform project with multiple gradle modules.

Could not create an instance of type org.jetbrains.kotlin.gradle.targets.js.subtargets.KotlinBrowserJs.
Failed to apply plugin [class 'org.jetbrains.kotlin.gradle.targets.js.nodejs.NodeJsRootPlugin']   > The Kotlin Gradle plugin was loaded multiple times in different subprojects, which is not supported and may break the build.
     This might happen in subprojects that apply the Kotlin plugins with the Gradle 'plugins { ... }' DSL if they specify explicit versions, even if the versions are equal.
     Please add the Kotlin plugin to the common parent project or the root project, then remove the versions in the subprojects.
     If the parent project does not need the plugin, add 'apply false' to the plugin line.

My root 

build.gradle.kts

 does not have a plugin block and my KMM module has the plugin block as follows.

plugins {
    kotlin("multiplatform") version Versions.kotlin
    application
    kotlin("plugin.serialization") version Versions.kotlin
}

I have some third party package. I want to add some custom classes to this package nand have access to all package private variables without touching the jar so in my project I create a class file and declare "package thirdparty.package" . Can I do that? Does it work in Kotlin or does it have to be somehow in the same folder ?

Does anyone have a link to Google's kotlin annotation processor mentioned in one of the talks of 1.4 event? Can't find it anywhere.

is there a way to ignore warnings for an entire project / module? FlowPreview in my case

Anyone got any recommendations for graph libraries in kotlin? Google’s guava.graph seems enticing, but lack of first class support for kotlin seems less appealing

Hello I am trying to create IR plugin that generates object. Anyone has experience with it?

Hi, what is recommended way to manipulate files on desktop native?

Hi, I'm running into this error when trying to use

async

Unresolved reference. None of the following candidates is applicable because of receiver type mismatch:
public fun <T> CoroutineScope.async(context: CoroutineContext = ..., start: CoroutineStart = ..., block: suspend CoroutineScope.() → TypeVariable(T)): Deferred<TypeVariable(T)> defined in kotlinx.coroutines

I'm not sure how much I can pare down my example, because it seems pretty specific to what I'm trying to do. Here's essentially the function

suspend fun getTile(params: SomeType): GetTileResponse {
        val cached = tileCache.get(params)
        if (cached != null) {
            return GetTileResponse.Available(cached)
        }

        val request = GetTileRequest(params)

        val deferred = async {
            makeRemoteRequest()
            .map { convertIntoResponse(it) }
        }

        return GetTileResponse.Loading(deferred)
    }

If I ask kotlin to generate an implementation of async, I get something which seems to look very similar to the definition of async (https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/async.html)

private fun async(block: suspend CoroutineScope.() -> Either<GetTileError, Bitmap>): Deferred<Either<GetTileError, Bitmap>> {
        TODO("Not yet implemented")
    }

How to split a list to sub list with random size? input:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

and random sub list size range from 0 to 4. output:

[0, 1]

[2, 3, 4, 5]

[6]

[]

[7, 8]

[]

[9, 10]

Each sub list size is random.

Hi everyone. Currently I'm doing this

providers.forEachIndexed { index, provider ->
  if (index == 0) {
    whatsNewPanel.setProvider(provider)
  }
  ...

Is there a function/extension which lets me move that

whatsNewPanel.setProvider(provider)

in a separate space? Possibly in the same call chain

When delegating "build" in IDEA to gradle.. can I configure that somehow? I had hoped I could create run configuration for

gradle build

and IDEA would use it on build. Anyone tried something similar? I guess what I would like is the ability to set a custom

-P

or

-D

property for IDEA tasks

Is there a way to use the very handy

lateInitVar.isInitialized()

from java?

Hello people 🙂! In our companys closed chat we have been arguing with kotlin developers about how is it safe to remove intristics calls with proguard in release builds. I think that removing this checks brings undefined behaviour, because method body will start to execute before potential NPE, for example:

fun f(a: String){
  sendData()
  //some a.length call (throws NPE)
}

with intrictics removed 'sendData' method will be executed. Another persons position is that business logic should be explicitly checked with some require(a!=null) check and developers should not rely on intrictics. What do you think?

Hi I need an identifier for a cache that is based on four strings and two ints. I need to do this without allocating (because I'll generate many of them in a tight loop). I think that java's hashCode for strings is always the same for the same characters, but I'm not quite sure how to combine multiple hashCodes

I'm planning to use this function to combine hashCodes. Does it make sense?

fun bitLength(n: Int) = floor(log2(n.toFloat())).toInt() + 1

fun combine(vararg numbers: Int): Int {
    var total = 0
    var prevBitLength = 0
    
    for (num in numbers) {
        total += num shl prevBitLength
        prevBitLength += bitLength(num)
    }
    
    return total
}

Why I can’t convert a String (number with decimal) into Int directly?

fun main() {
    val stringDouble = "420.0"
    val int = stringDouble.toIntOrNull()
    assert(int != null) // failed
}

I’m trying add kotlinx-serialization(and something pure kotlin library) dependencies for KMM project, Is there a need to add for each platform(Android/iOS) separately, or just add COMMON dependencies?