How to call a function defined inside a companion object, if I can only get to the companion object by reflection, so:

SomeClass::class.companionObjectInstance

IDK, maybe I have a brain freez, but I can't figure out how to model it without lower bounds. (The apply method, that takes list and returns new list with modifications applied)

interface ListModification<out E> {
	fun applyTo(target: MutableList<in E>)
	fun <T> apply(target: List<T>) : List<T>
			where E : T
}

val commands: MutableSet<Command<JDACommandSender>> = mutableSetOf()
get() = Collections.unmodifiableSet(field)

My goal is to allow the class itself to modify

commands

directly, but others to only be able to get an unmodifiable version of the contents. Is there any direct way to achieve this?

recently I came across this article -> https://medium.com/google-developer-experts/companion-objects-kotlins-most-unassuming-power-feature-fb5c0451fbd0 It showcases some great use-cases but it made me a bit confused For example, what really is the difference between

fun interface Validation : (String) -> Boolean {
    companion object
}

val Validation.Companion.validateEmail
    get() = Validation { it.isNotEmpty() }

val Validation.Companion.validatePassword
    get() = Validation { it.isNotEmpty() }

val isFormValid = Validation.validateEmail("email") && Validation.validatePassword("password")

and

typealias Validation = (String) -> Boolean

val validateEmail: Validation = { email: String -> email.isNotEmpty() }
val validatePassword: Validation = { password: String -> password.isNotEmpty() }

val isFormValid = validateEmail("email") && validatePassword("password")

What are use-cases where first one would add value over second one? Or is this just semantic difference?

what’s the cleanest/most kotlin-idiomatic way to define a method which can take one of 3 types of object, short of declaring 4x separate methods? The types in question are Date, String, Bool and Int. Wondered about a

sealed class

unsure if this is the most appropriate approach.

oh no, april 1 is coming

message has been deleted

Hello, I’m trying to create a utility class that’s Java compatible. I was able in the past to do the following:

Intents.kt

@file:JvmName("IntentsUtil")
@file:JvmMultifileClass

open class Intents {
    companion object
}

PlayStoreIntents.kt

@file:JvmName("IntentsUtil")
@file:JvmMultifileClass

fun Intents.Companion.viewAppOnPlayStore(appUri: String): Intent =
    Intent(Intent.ACTION_VIEW).apply {
        data = Uri.parse(appUri)
        setPackage(Apps.PLAY_STORE.url)
    }

When invoked Java side was able to simply:

IntentsUtil.viewAppOnPlayStore("foo");

Now however, it requires me to do:

IntentsUtil.viewAppOnPlayStore(Intents.Companion, "foo");

Any idea to why that is? How can I avoid passing the Companion object?

Hi, im looking at detekt configuration. Is there any popular detekt config next to the default one like there is with PMD etc? Or to the people here using detekt, what configuration are you using?

Hi, what's the most efficient way to remove an element from a mutable set of ByteArray??

val b = "1".toByteArray()  
val s = mutableSetOf("1".toByteArray())
    
s.remove(b) // <== this does not work, probably because "1".toByteArray() != "1".toByteArray()

s.removeIf { b.contentEquals(it) } // <= this works

Just found myself writing these…

fun Runnable.toFun(): () -> Unit = { this.run() }
fun Function0<Unit>.toRunnable(): Runnable = Runnable { this() }

fun <T> Callable<T>.toFun(): () -> T = { this.call() }
fun <T> Function0<T>.toCallable(): Callable<T> = Callable { this() }

and then wondered a) do they already exist or b) is there a better way?

Are there any plans to support module-wide sealed classes?

This message was deleted.

is

${'\n'}

the only way to add a new line in triple quotes?

hi everyone. i am building a project with tornadofx (javafx kotlin) and opencv (native libraries with optional java wrappers). The application should later run on windows, macos and linux. At the moment i struggle to include the native libraries into my kotlin multiplatform project (gradle kotlin) and googling is unfortunatelly pretty hard because most examples are for android and ndk ... which is not what i am using. Is there an example how to include native libraries in kotlin multiplatform projects or maybe even include OpenCV as a CMake based module?

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are there any plans to make user friendly compiler error message a priority for kotlin like for example elm, rust or scala have done? https://www.scala-lang.org/blog/2016/10/14/dotty-errors.html https://elm-lang.org/news/compiler-errors-for-humans https://blog.rust-lang.org/2016/08/10/Shape-of-errors-to-come.html

trying to use reflection in 1.5.0-M2 and somehow the get doesn't compile since it expects object of type Nothing and not Transaction:

fun getProperties(t: Transaction) {
    t::class.memberProperties.forEach {
            println(it.name)
            println(it.get(t)) // gives error since it doesn't expect type Transaction 
    }
}

What's the difference between Retrofit and okHttp?

hi folks, my name is Fernando Avanzo, and i work with kotlin above two year, all what i learned is throught study of the documentation Jetbrains , webninars, and of the comunnity tutorials in Medium. I would like to ask, if have a offcial program of certification of koylin? how the OCJP by Oracle? If has, what i need do to get? Thanks for the help guys

Does anyone else find trailing lambdas confusing? Especially when learning, I wish I could tell IntelliJ to reformat all code to be explicit about trailing lambdas - it would really help me to understand what is actually going on. Or perhaps a different block delimitator could have been chosen, besides { }, to make it clearer. Or maybe it's just me!

Are there any tools to "visualize" your code line by line?

We (still) use slf4j/logback in our Kotlin code. Currently, we define a

val logger: Logger = LoggerFactory.getLogger(Foo::class.java)

in the companion object of a class

Foo

. I remember a discussion about defining this as a class property instead of as a companion object property (which would then allow to use

val logger: Logger = LoggerFactory.getLogger(this::class.java)

) but I can't find it anymore. What is current best practice here ?

slightly connected Q: the return type of a Java method

getFoo

which returns an object of type

Foo

(and never returns

null

) is

Foo!

. Should I (a) ignore this and use

val foo = getFoo()

(b) use

val foo: Foo = getFoo()

or (c)

val foo = getFoo()!!

I have just started looking at Kotlin, I have been using F# on .NET for a while now and I am liking Kotlin. I am missing pipe operator in Kotlin though, is there any plan to bring the pipe operator to Kotlin?

The other question I have is with regards to Exposed, is there any tool to generate structures for existing database?

Hi, is there a beginner channel to ask questions related to the logic in the code? The code is related to if else and recursive.

Is there some way to make kotlin assume that any values coming from a java method or class are nullable?

I got this error

java.lang.AssertionError: Enum class does not have .values() function

when make enum

Serializable

Kotlin 1.4.31 Canary 13 Custom Serializer for this enum doesn’t help, (((