I'm wondering if contracts would help to get rid of that !!:

dtos.filter { it.field != null }
    .map { OtherDto(it.field!!, it.otherField, it.anotherField) }

inline fun test(vararg properties: Pair<String, Any?>) {
   //(uses pairs)
}

test(
   "a" to 1,
   "b" to 2,
   …
)

Can the compiler optimize away the

Pair

allocations and maybe even the boxing? if so, is

inline

needed for that to happen?

is there a good equivalent of a "multiset" in Kotlin? I don't care about order. I simply care about element count and I want to compare equality between to multisets.

Hi, when exactly package level variable gets initialized? when it is imported like in python?

Hello, why this does not compile? Is it some bytecode limitation? It compiles fine if functions are declared inside a class.

fun main() {
    fun foo() {
        bar()
    }

    fun bar() {
        println("Called")
    }

    foo()
}

Hello everyone, I have a question about interoperability between Kotlin and Java. I have a Kotlin class

A

extend from a Java class

Base

which has a static function

f()

. When I called

A.f()

in a Kotlin file the IDE give an error ” Unresolved reference: f “. But when I called

A.f()

in a Java class, It works fine. I want to know the reason and maybe correct implementation. Thanks!

Hello, I've a question about maps and potentially lambdas, I've a map mapping int to objects creation, something like this: val menuIdToItems: Map<Int, MyObject> by lazy { mapOf( menu1 to Item1.newInstance(), menu2 to Item2.newInstance(), menu3 to item3.newInstance(), ) It's working fine, BUT I just realised that when I evaluate menuIdToItems[menu1], I actually need a NEW INSTANCE every time I evaluate menuIdToItems[menu1]. Right now, If I evaluate menuIdToItems[menu1] two times, second time will return the same instance that I got the first time. Is there a way to do this using a map?

Good morning. Is there a channel for kotlinx.serialization?

Is it possible to iterate on all kclass types of a sealed class? I use moshi and use https://github.com/square/moshi/blob/master/adapters/src/main/java/com/squareup/moshi/adapters/PolymorphicJsonAdapterFactory.java Therefore I need to registert all children of a sealed class and I want some compile time safety and want to make sure I handled all sub classes.

Hello ! I would like to do something on a list, i think there is a function i don't know but i don't find it... Here is my code :

val stringList = somethingList.map {
   it.str
}

if (stringList.isNotEmpty()) {
   doSomethingWithMyList(stringList)
}

And i would like to do something like that

somethingList.map {
   it.str
}.unknownOperation { // here i need help
   doSomethingWithMyList(it)
}

Hi. I'm implementing a toy ServiceLocator kind of thing. Is it possible to achieve something akin to this via the type system?

fun registerService(interface: ???, impl: ???) { ... }

registerService(UserInterface::class, UserService()) // ok
registerService(CarInterface::class, CarService()) // ok
registerService(ChairInterface::class, TableService()) // fail, because TableService does not implement ChairInterface

Can anyone suggest an alternative to ktor-client websockets? They seem fundimentally broken and unusable

Is there a way to get sealed class smart casting to work when filtering a collection on an

is

predicate and then doing operations on the subclass further down the chain?

Hello all! Has anyone had luck mocking Exposed using MockK?

Hello, I got this error after try to run generated jar any idea ?

➜  life-drain git:(master) ✗ ./gradlew build && java -jar build/libs/life-drain-1.0-SNAPSHOT.jar
w: /home/kotl/repo/watchanimeonline/life-drain/src/main/kotlin/com/life/drain/libs/GetMovieUrls.kt: (65, 33): Unnecessary non-null assertion (!!) on a non-null receiver of type List<String>

BUILD SUCCESSFUL in 3s
6 actionable tasks: 6 executed
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: kotlin/jvm/functions/Function1
	at java.lang.Class.getDeclaredMethods0(Native Method)
	at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
	at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
	at java.lang.Class.getMethod0(Class.java:3018)
	at java.lang.Class.getMethod(Class.java:1784)
	at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
	at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Caused by: java.lang.ClassNotFoundException: kotlin.jvm.functions.Function1
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 7 more

https://kotlinlang.org/docs/reference/reflection.html but how do I search for a method name by annotation, and then exec said method? seems more like this documents method references than true reflection.

@paulex use openjdk instead

Maybe a basic question, but I want to filter a list, call a function with each matching element, then collate the results to a new list. Is there a more elegant way than this:

val filtered = all.filter { it.foo }
   .map {
      callFunction(it)
      return it
   }.toList()

Did you try using

in T

?

Kotlin doesn't have a notion of union types, so I imagine it would either smart cast it to the nearest superclass (probably

Entity

), or not cast it at all.

Why have a holder, why not just have a sealed class

Is there a way to use interface delegation and access the delegate without making it a constructor parameter? 🤔

everytime I try to compile it says

error: invalid method declaration; return type required

Next Kotlin meetup in Paris if anyone is interested :) http://meetu.ps/e/G6sXz/vNnx2/d

are their code quality tools that work with kotlin? checkstyle, spotbugs, and error prone are what I use with java.

does kotlin make use of jigsaw modules?

what's the proper way to define a void fun

if i have a

List<Tide>

where a

Tide

has a field

tide

that is of type

Float

, what is the best way to sort by the

tide

field? I tried

tides.sortedBy { it.tide }

but it throws a ClassNotFoundException

class RideException(private val errorCode: ErrorCode, t: Throwable) : Exception(t) {

    constructor(errorCode: ErrorCode) : super(errorCode.exceptionMessage)
}

getting error near

super

-> primary constructor expected