very very dumb question. I have a

csvReader.open(file) { ... }

function from a library. The problem is the lambda is not suspend-aware. Is there any way to call a suspend fn in the lambda there other than calling runBlocking? FWIW, this is all inside a suspending function, so I do not want to do

runBlocking

inside a

suspend

function. It just feels so wrong.

I'm trying to use Jacoco, but it detects a lot of classes that shouldn't have coverage, such as Kotlin synthetic classes

Is there a way to add a "scoped" extension to class A inside of class B, outside of class B? For example, I tried this but it complains:

class Foo {
   fun String.someStringExtension() { ... }
}

fun Foo.String.someOtherStringExtension() { ... }

@bbaldino I looked this up one time and pretty certain this feature is still in proposal phase. I agree that it would be incredibly useful. I can't find a reference at the moment, but Kotlin language proposals are found here .

Can we have some sort of bounded (must-be-same) star projections?

fun <T : SomeClass<*>> SomeOtherClass<*>.function() {...}

Such that we can guarantee the two star-projections must be equal? I know we can introduce another generic, but that'll lead to redefine that explicitly twice like 

function<T<E>, E>

 when calling the function. So is there any way we can omit that extra generic and use some implicit kind of thing?

Is the

x

is

kotlinx

for ‘extensions' (like in

javax

) or for ‘experimental'?

Hi there! I've seen that with 1.4 SAM intefaces are now converted properly between Kotlin and Java. This is great, but there is a problem, however: I still can't define functions that return void. For example if I have a signature like this:

fun someFun(fn: (SomeClass) -> Unit)

I have to explicitly return

Unit.INSTANCE

from Java code. Is there a way to fix this (besides writing a helper function)

Looking at the experimental

Duration

implementation in

kotlin.time

I can see the extension methods from

Int

and

Long

to

Duration

. However I’d like to use the Java function:

public static Duration ofSeconds(long seconds, long nanoAdjustment)

…which I can’t see an implementation for. Any thoughts on how to achieve the same in kotlin?

Hi folks! Is there a best alternative in Kotlin than using java nio Bytebuffer?

val bos = ByteArrayOutputStream()
DataOutputStream(bos).use {
   it.writeInt(mydata)
}
ByteBuffer.wrap(bos.toByteArray())

I was googling around but haven’t found anything really.

Hello everyone, does anyone know, why the first four functions return false?

fun main() {
    fun main() {
    val arr1 = Array(0) { "" }::class
    val arr2 = arrayOf("")::class
    val arr3 = Array::class

    println(arr1 == Array::class)               //false
    println(arr1.isSubclassOf(Array::class))    //false
    println(arr2 == Array::class)               //false
    println(arr2.isSubclassOf(Array::class))    //false
    println(arr3 == Array::class)               //true
    println(arr3.isSubclassOf(Array::class))    //true
}

I think thats a bug.

suspend fun jobLifecycle () = coroutineScope {
   val job =  launch{
       println("Working....")
       delay(2000L)
       println("Done !")
    }

    delay(1000L)
    job.cancel() 
    // delay(1L) i have to do it to print correct value of job.isCompleted below
   
    println("isCompleted: ${job.isCompleted}") // it is printing "false" but if i delay for some time after cancelling the job it prints  "true".
   
}

is it my computer or it really takes some time to move job from cancelling to cancelled state where isCompleted becomes true after cancellation of job or is there something im missing out pls review..

Hi all, I have a java class with a method I want to override in my kotlin code. The method returns java.lang.Object, meaning it can possibly be null, and I would like to return null from my kotlin implementation. The problem is that I am not allowed to specify the return type of my method as

Any?

when the method I'm overloading has return type

Object

🤔

Hey everyone! Today I finally started using sealed classes, which is great. But I came to a point where I'm not sure how to handle it in the correct way:

.map { (payment, requestModel) -> steps.performRequest(payment, requestModel) 
.filter { (_, result) -> result is ApiResult.Success }
.map { (payment, result) -> steps.update(payment, result) }

After performing the request, I want to filter out all results which were not of Type

ApiResult.Success

Unfortunately the compiler does not allow this, since

update()

is expecting

ApiResult.Success

. What did I miss there? My only solution right now is to set the

result

Parameter to ApiResult and add a

require()

block in my update function, but I'm not really happy with that.

My brain is fried, I don't understand this, anyone a quick helping hand?

Unnecessary safe call on a non-null receiver of type Int?

Why is

Int?

non-null? Why is it wrong to use

?.

on it?

Kotlin Public Roadmap Through Spring 2021 Today, we’re excited to announce the public roadmap for Kotlin. This document describes the biggest projects our team is working on right now. It has a 6-month time frame and will be updated every 3 months. Each item on the roadmap represents a project with a linked YouTrack ticket. If you have a question about […]

hi i have a question deos kotlin have sound null safety?

👋 Hi there! I've been a Kotlin fan way back since M11 or so and am now starting to play with multi-platform. We've got some functions we'd like to share between JS and JVM runtimes, but we already have a JS-based application that we don't want to re-write in Kotlin quite yet. I've done the tutorial here [1], which is fantastic, but I'm not sure how I can use NPM to install it directly and call into the Kotlin library from my JavaScript project. Can anyone offer any pointers? I've maven-published the library, but I see no mention of NPM or how to use a kotlin library with NPM in this tutorial. [1]: https://kotlinlang.org/docs/tutorials/mpp/multiplatform-library.html

having trouble converting a small bit of java to kotlin.

for (Map<String, String> serviceOutputs; (serviceOutputs = resultReader.read(header)) != null; ) {
    try {
        final double elapsed = Double.parseDouble(serviceOutputs.get("__elapsed"));

gets converted to

var serviceOutputs: Map<String, String>
while (resultReader.read(*header).also { serviceOutputs = it } != null) {
  try {
    val elapsed = it["__elapsed"]!!.toDouble()

which doesn’t work because

it

can be null, and

serviceOutputs

can’t be null. I can correct this to:

var serviceOutputs: Map<String, String>?
while (resultReader.read(*header).also { serviceOutputs = it } != null) {
    serviceOutputs?.let {
      try {
        val elapsed = it["__elapsed"]!!.toDouble()

but that is pretty messy and not indicative at all of what is happening.

serviceOutputs

can never be null in the block, and using a

let

is messy. Any way to accomplish this a bit cleaner?

Is this a bug? E is not recognised as Int for example below

Hi guys, is it possible to get type from Any? I need to check whether Any is Collection<String>. I tried something like

inline fun <reified T> isTypeOf(any: Any?): Boolean {
    return any is T
}

val isTypeOf: Boolean = isTypeOf<Collection<String>>(Any)

my Any is ArrayList of String.

iyo is doing something like this bad practice? (using KMongo here but it really doesn’t matter)… I just feel there should be some abstraction layer between mongo and the app, but building the abstraction layer usually is just a matter of writing brain-dead code

Is there a way to enforce curly braces for if statements and loops in Kotlin, or even better, automatically add it (like the code formatter in Ktlint does)? I noticed there are options in

.editorconfig

but it doesn't seem to do anything

ij_any_if_brace_force = always
ij_any_for_brace_force = always

Ktlint seems to have such options, but it's marked as experimental and it will only show warnings What are other teams using for automated code formatting in Kotlin?

Hi everybody!! Acording to the documentation,

async()

exposes users to exceptions:

Coroutine builders come in two flavors: propagating exceptions automatically (launch and actor) or exposing them to users (async and produce).

But then, I'd expect wrarping the

await()

call in

try... catch

would just allow me to catch the exception produced in the

async

block. Instead, it seems the

async()

block's exception is handled by the supervisor. That gives me an odd behavior in this example:

import kotlinx.coroutines.*
fun main() = runBlocking<Unit> {
    try {
        val res = async {
          // suspend fun that ends up throwing ArithmeticException
          failedConcurrentSum()
        }
        res.await()
    } catch(e: ArithmeticException) {
        println("Computation failed with ArithmeticException")
    }
}

The odd part is that the exception is caught by

catch

but, at the same time, it is thrown by runBloking. See an executable snippet here: https://pl.kotl.in/sWjfVuEDr. Why is that so? What am I missing here??

does dokka not have any support for something like <pre> or an equivalent that would preserve formatting/linebreaks?

inline fun <T, K, R> Grouping<T, K>.fold(
    initialValueSelector: (key: K, element: T) -> R,
    operation: (key: K, accumulator: R, element: T) -> R
): Map<K, R>

Semi related but the relationship between

aggregate

and

fold

for

Grouping

seems kind of fuzzy to me. It seems like this version of

fold

is just an awkward, two lambda version of aggregate. But then, the simplest case is handled most nicely by the

fold

overload taking a simple initial value. So the useful functionality is kind of spread between them, and yet aggregate is missing the most useful overload (IMHO). Just curious if there are reasons I'm missing why the API is this way. The first time I went to use

Grouping

it felt a bit clunkier than I'm used to in Kotlin.

Hello everyone, the compiler forced me to add an else branch in the following snippet. What's the reason behind that?

return when ((1..2).random()) {
            1 -> "ABC"
            2 -> "XYZ"
            else -> "???"
        }

The range only includes 1 and 2 and random returns an int.. 🤔

If I have a base class with few hundred fields (basically constants, but not declared as static) will the derived classes also have hundreds of fields in memory? or will the JVM somehow optimize that?

What's a good use case for an observable delegate? I digged into it and I can't really find a good example where I would defintly choose this one over anything else. I'm a backend guy. A quick look at google suggests that it seems to be more of an android thing? I came up with the topic while preparing a little kotlin intro for our Java devs, and thought that I could also show the builtin delegates.

Since the Generic information is present at the compile time, is it possible to access the generic type(s) of an object using the contracts, or any plans in the future?