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I have

method(input:Set<X>):Set<X>

, which wants to transform each element of the (small) set, seemingly a natural fit with

.map { }

, but, the transformation can produce invalid individual values, and if that occurs the method's result will be

emptySet()

. In other words, under some conditions i want to short-circuit the mapping and just return the empty set. I am wondering if there is some clever stream-ish/sequence-ish way to accomplish this, or should I just go with a for-in and a result accumulator?

Is there a way to add a companion object to a class from another library. So that i can add extension methods to it. Trying to find a nice way to do SomeDtoClass.generate(10) for a testing solution. Or are there som other nice way?

Hey! Is there a way to make a TCP listener with kotlin native?

Hey anyone has expert in paging 3 library. I need help. I am working on unlimited data with Viewpager 2 and Paging library. I successfully created the logic to create unlimited pages by the help of paging source. I am swiping single pages by buttons in both direction. But some issue like a weird race scenario where the smooth scroll behavior in ViewPager is attempting to do an animated scroll to an absolute position, but Paging is able to PREPEND items to the front of the list faster than the animation can scroll there. Can anyone know how to solve the problem. I asked in stack overflow but i didn't get it

I just noticed a behavior change in Kotlin 1.4 (after finally upgrading a project from 1.3):

mapOf("a" to 1L, "b" to 2)

now has a type

Map<String, Long>

while it had type

Map<String, Any>

in 1.3. This caused a runtime error because the

2

was passed to some Java code which then casts it to an

int

. It was easy enough to fix by using `mapOf<String, Any>("a" to 1L, "b" to 2)`but it makes me wonder: could I somehow prevent the automatic promotion of the

2

to a

2L

?

Today I looked for something like a conditional let or run, but found nothing. How about this - would something like it make sense in the standard library? https://pl.kotl.in/EI387hmPU

inline fun <T> T.thatIf(condition: Boolean, block: T.() -> T) = if (!condition) this else block()
inline fun <T, R> T.thatIf(condition: Boolean, default: R, block: T.() -> R) = if (!condition) default else block()

inline fun <T> T.letIf(condition: Boolean, block: (T) -> T) = if (!condition) this else block(this)
inline fun <T, R> T.letIf(condition: Boolean, default: R, block: (T) -> R) = if (!condition) default else block(this)

val ALL_TO_LOWER = true
val APPEND_SIZE = false

fun main() {
    val foo = "Foo"
        .thatIf(ALL_TO_LOWER) { toLowerCase() }
        .thatIf(APPEND_SIZE) { "$this ($length)"}

    val bar = "Bar"
        .letIf(ALL_TO_LOWER) { it.toLowerCase() }
        .letIf(APPEND_SIZE) { "$it (${it.length})"}
    
    println("$foo $bar")
}

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Hi everyone. I wanted to know, how can we integrate network and database interaction capabilities in Kotlin Jetpack compose for Desktop apps ? If anyone have worked on this part, may also share github repositories if any..

I really need to call a Kotlin method with reified type parameter from Java. Is there no workaround? I am willing to add utilities or even use reflection if needed.

Another change is a set of new factory functions for creating 

Duration

 instances from integer values. They are defined directly in the 

Duration

 type and replace the old extension properties of numeric types such as 

Int.seconds

.

I saw ☝️ in the release notes for 1.5 RC, and I'm curious what the reasoning is for deprecating the extension properties. I found it to be a very nice API. Was it about polluting the namespace?

Is there a reason I cannot write

if (list is List<MyClass>)

? Compiler forces me to write

if (list is List<*>)

. So I have to write

if (list as? List<MyClass> != null)

to smartcast my list

when implementing custom properties,

ReadWriteProperty

for example, it uses

kotlin.reflect.KProperty

. do properties use reflection or

KProperty

is there to enable reflection?

Should smart cast work in case of

if (myNullable?.status in listOf(FOO, BAR)) { <myNullable not nullable here> }

In 1.5.0-RC it's still necessary to specify languageVersion/apiVersion properties (at least in Maven) to use sealed interfaces. Is this expected?

I have:

interface UseCase<in Request : Any, out Response: Any> {
    suspend fun execute(request: Request): Response

    suspend operator fun invoke(request: Request): Response = execute(request)
}

But when I call an implementation of it in a unit test, it throws:

usecase.SomeUseCase.invoke(Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
java.lang.AbstractMethodError: usecase.SomeUseCase.invoke(Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;

what could this be?

Curious what people think of this pattern:

when (enumValue) {
  Enum1, Enum2 -> doSomethingImperative()
  else -> Unit
}

as an alternative to

val certainEnumConstants = setOf(Enum1, Enum2) // defined in an object, so allocated once for the life of the runtime - recent edit in light of confusion in thread
if (enumValue in certainEnumConstants) {
  doSomethingImperative()
}

I like the lack of need to define and name a

val enums: Set<EnumType>

in the first, but I don’t like the need for an

else

branch.

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when I dont' use the result of the builtin

copy()

function of data classes Intellij highlights the code as a warning (with error of "Unused result of data class copy"). is there a way to get warning activated for my own functions, when I don't use the result value?

does anybody know how https://pastebin.com/5JYdjBeE differs from https://pastebin.com/jr3DxT5a ?

Is there a standard fun that return self when non-null or using the default? for example:

val a: Int? = null
a.foo { 0 } // 0

val b: Int? = 1
b.foo { 0 } // 1

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Hi everyone. Is it possible to sum average values of several Int lists in more beautiful way, to reduce code duplication?

val red = data.red.map { it.toUByte().toInt() }.average()
val green = data.green.map { it.toUByte().toInt() }.average()
val blue = data.blue.map { it.toUByte().toInt() }.average()
val luminance = red + green + blue

Hey, a friend of mine is doing a community driven game, he is doing it using compose, thought it might interest some people: https://twitter.com/imakeyouagame/status/1385024136666304516?s=20

Hello everybody. I'm fond of Kotlin, but as I see that Kotlin is used for Android and I use it for Android apps. Why Kotlin doesn't become popular? And why programmers don't use Kotlin for web, desktop apps. I've never seen job positions for Kotlin Developers. Why? There are articles about Kotlin that they say that Kotlin will be one of the most demanded programming languages. But I don't see this.

I just discovered that

Iterable<T>.map

returns a

List<R>

not the original data structure (whatever implemented the

Iterable

. This seems very strange to me, is it expected? I would expect the

map

function to affect only the contents of the data structure, not the data structure itself.

Maybe stupid question but why kotlin doesn’t have a unaryTimes operator? I a not sure if this does make sense mathematically but I am facing a situation where it would be really handy to overload the * while writing a DSL like this

foo { // will invoke some object as this
    0 {
        // create some list based on Foo and get 0 index of list 
    } 
    * {
        // create some list based on Foo and get all entries of list
    }
}

https://kotlinlang.org/docs/operator-overloading.html