How do I access the delegating instance when using delegated inheritance. Is it possible?

interface Validatable {
    fun validate()
}

class Impl() :
    // both these extend `Validatable`
    Validatable1 by Validatable1.Impl(),
    Validatable2 by Validatable2.Impl(),
    Validatable {

    override fun validate() {
        // how do I call:
        // validatable1.validate()
        // validatable2.validate()
        
        // or bonus - can I access the `Validatable1.Impl()` instance at all?
    }
}

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Heya folks! My friend and I are streaming how he learns to write in Kotlin and I learn GameDev: https://twitter.com/asm0di0/status/1588103011590610946 In ≈10 minutes!

Is there an easy way to stop any stdlib functions from being imported automatically? I just got bit again when I accidentally used

value.toString()

instead of

value?.toString()

. I'm not a fan of

Any?.toString()

, and I'd like to just get rid of it locally if possible.

trying to use

sealed interface

, Idea's popup says

The feature "sealed interfaces" is only available since language version 1.5

then I click it and in my

build.gradle.kts

it adds

val compileKotlin: KotlinCompile by tasks
compileKotlin.kotlinOptions {
    languageVersion = "1.5"
}

but

sealed

is still marked as error and compiling fails:

> Task :buildSrc:compileKotlin FAILED

3 actionable tasks: 1 executed, 2 up-to-date

e: /home/elect/IdeaProjects/vkk/buildSrc/src/main/kotlin/vkk/parsing.kt: (79, 1): The feature "sealed interfaces" is only available since language version 1.5

hey everyone. I’ve got a question about interfaces. I can’t yet understand the best way of how to decide which concrete implementation of interface to use. Let’s imagine, that I have

ServiceInterface

that has 2 implementations

ConcreteService1

and

ConcreteService2

It’ll have one function

doWork()

. I need to use one implementation or another based on some property, that comes as a parameter. And I don’t understand where do I resolve which concrete class to use.

class SomeClass(
    val someService: ServiceInterface
) {
    fun someFunction(status: String) {
        when(status) {
            "ACTIVE" -> someService.doWork() // or even better to return the instance of service
            "INACTIVE" -> someService.doWork()
        }
    }
}

Could someone give a hint?

I'm trying to get started writing my own full-stack applications in Kotlin, however, I'm not sure how to properly set up live reloading. Basically, I'd like to have a Kotlin/JVM backend and a Kotlin/JS frontend. I'd like the JVM server to serve all the files and the JS frontend to compile into JS to be run in the browser. Is there a way to enable live reloading in such a setup?

instantiating a class, there is a field

comment

which I'm initializing by delegation

sealed class Type(line: String) {
    val comment by line

However there might be some cases where I need to set it explicitly via constructor.. idiomatic code

sealed class Type(line: String, val comment: String = by line)

what's my best option for this?

Hi, How to figure out this compiler error?

Type parameter output is declared as 'out' but occurs in 'invariant' position in type Flow<PagingData<output>>

abstract class PaginatedFlowUseCase<in Input, out output>(
    private val dispatcher: CoroutineDispatcher
) {
    operator fun invoke(input: Input): Flow<PagingData<output>> {
        return execute(input).flowOn(dispatcher)
    }

    protected abstract fun execute(input: Input): Flow<PagingData<output>>
}

But it works when changing PagingData to kolin.Result class

In swift, we can confirm to any protocol / interface using extensions. Can we add interface conformance to certain class using extension in Kotlin?

Somehow all of my tests stopped seeing

internal

members of the tested classes (even though they are in the same Gradle module). Generally I made some changes which currently broke the build, but they are not related to the internal function/properties. So the project indeed should not build, but the error message is definitely a false positive.

HI, I saw in some projects for handling dependencies something like that

object Libs {

object Google {

…

object Test {

……

}

object Firebase {

…..

}

}

object Accompanist {

……

}

object Gson {

…..

}

object Log {

…….

}

//other objects ...

}

Is it ok to creates many object like this just to handle dependencies ? for me it’s not :(

I just got to know that

Contracts are not allowed for operator functions

Why is that?

is it idiomatic to use

T?

like an optional of type

T

?

Hello all, I'm trying to run the tests, but it's giving the following error.

Cannot inline bytecode built with JVM target 17 into bytecode that is being built with JVM target 1.8. Please specify proper '-jvm-target' option

my config

tasks {
    test { useJUnitPlatform() }
    compileKotlin { kotlinOptions.jvmTarget = "17" }
    ...
}

What am I doing wrong?

Why is the second argument to

require()

a function rather than a string? I can think of two possible answers: 1. In case constructing the message is expensive (seems unlikely). 2. In case we want to do additional processing before throwing the exception, such as logging or cleaning up. I'm teaching about Kotlin exceptions, so I really want to get this right.

I have the following property declaration in a companion object:

class WordleGame(val secretWord: String) {
    companion object {
        private val words = java.io.File("words.txt").readLines()

        fun playGame() {
            val game = WordleGame(words.random())
            ...
        }
    }
}

fun main() {
    WordleGame.playGame() // ExceptionInInitializerError
}

Is there a clean way to catch a

FileNotFoundException

? I can catch a

ExceptionInInitializerError

in

main()

and pull out its cause, but I'm hoping for something easier to explain to students, possibly restructuring the code.

is there a way I can define a

NULL

as a companion object of an inline class using a type parameter?

@JvmInline
value class Ptr<T>(val adr: Adr = 0L) {
    companion object {
        val NULL: Ptr<*>
            get() = Ptr(MemoryUtil.NULL) // Not enough information to infer type variable T
    }
}

fun main() {
    println("%s %s".format("hi", "bye"))
    println("%s %s".format(*arrayOf("hi", "bye")))
    println("%s %s".format(arrayOf("hi", "bye"))) // java.util.MissingFormatArgumentException: Format specifier '%s'
}

Anyone know why it goes wrong with a pure array declaration?

I am having an issue related to object declaration (something like

object MyObject{ }

). In my app, there's a snippet that looks like this

fun myFunction():Any{
    try{
        // do things
    }catch(e:Throwable){
        return MyObject.sideEffect()
    }
}

object MyObject{
    fun sideEffect():Any{
        //....
    }
}

the code inside the try block will throw an StackOverflowError under certain condition. The StackOverflowError is caught, and a side effect is emitted. This side effect is produced by an object declared in a different file, and half of the time, it will throw this exception; while on the other half, it runs just fine.

Could not initialize class com.example.MyObject
java.lang.NoClassDefFoundError: Could not initialize class com.example.MyObject

However, if I run this

val mo = MyObject

before calling

myFunction()

, the

NoClassDefFoundError

exception is never thrown. Maybe this has something to do with the fact that MyObject is lazily allocated according to the official document. Could someone point me to a more in-depth document on object declaration? I need to know what is going on badly :melting_face: Thank you.

Hello, I'm new to kotlin and I wanna know is there any SDK for kotlin ? I'm using inteliij IDEA, as you can see, there is a JDK but not a SDK for kotlin. and I also wanna whether I should download some kotlin-ish thing with

apt

? I'm using ubuntu

Unable to add type when declaring a list of strings 1. i'm not sure if i'm doing something wrong, i recall being able to declare a list type to be string with the following code below

val nameList:List<String>=listOf("Apple","Orange","Pear")

->> CODE A 2. I get the following error below "Property getter or setter expected" 3. i had to write as following

val nameList=listOf<String>("Apple","Orange","Pear")

which is fine with me, but why cant i use Code A, hope someone can advise me

isn't possible to add an extension on a inline class companion?

I have a

sealed class

with many

data class

es that subclass it. I get these subclasses from some stream I want to build some sort of state machine that changes its state based on the last seen subclass. what’s a cheap/easy way to encode/decode the type of the seen class?

basically serialize/deserialize just the class kind, I don’t care about the state of the class itself

What's the best way to shorten this code ? All call() methods take and return a list. Is there a way to chain all these operations ?

var list = serviceA.call(list)
list = serviceB.call(list)
list = serviceC.call(list)
list = serviceD.call(list)

How do I read an exception like this? Line 69 doesn't exists and line 10 is just the constructor

java.lang.NullPointerException: null cannot be cast to non-null type kotlin.Number
	at com.apurebase.puredynamic.repository.user.mapping.UserMapping.<init>(UserMapping.kt:69) ~[main/:?]
	at com.apurebase.puredynamic.repository.user.mapping.UserMapping.<init>(UserMapping.kt:10) ~[main/:?]

Hello! How to make Kotlin compiler issue an error when package name is not matching directory path?