I have a simple example of using select{} on mutex.onLock: https://gist.github.com/pambrose/4eb82e623161ee7758551ad6a9649ab6 Based on the docs and the name “onLock” I am expecting the select to take place when an unlocked mutex is locked. However, I am seeing the opposite behavior, i.e., if I use locked mutexes, I am seeing the select take place when the mutex is unlocked. The docs for Mutex.onLock say that it “selects when the mutex is locked.” Given the behavior I am seeing, I would expect the name to be “onUnlocked”. I would appreciate someone setting me straight on this.

Hey guys. Is there a way that I can call a method in Java that have a generic boundary? Let’s say my method in Java:

public static <T extends A&B> void methodA()

Where A B are different interfaces I can call the method in Java without any type like this:

methodA()

But when I call that method in kotlin I don’t know what type I should give to it

methodA</*What Should I put it here?*/>()

Any ideas?

Any idea for abstraction CaptchaType? I do it this way because the annotation parameter only receive const value( compile-time constant )

Hi! I just recently started trying to use coroutines (in an app that uses spring boot, fwiw) and I keep getting this error:

java.lang.ClassNotFoundException: kotlin.coroutines.jvm.internal.SuspendLambda

I’m using gradle to build the project and have this in place

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.1.1'

(using old version b/c we’re on kotlin 1.3.20 for now) Any ideas what might be going on?

Hello everybody , Do you know any open source application which implement this concept

finite state machine

? I found some libraries implemented this concept but need more information to implementing this .

<https://github.com/Tinder/StateMachine>

<https://github.com/open-jumpco/kfsm>

i have a mutable list of objects, and a reference to one of the objects in that list. i want to keep every object from start until (including) the object i have a reference to, and drop everything that comes afterwards. I see countless ways to do this (e.g.

myList.dropLast(myList.size - 1 - myList.indexOf(thatObject))

) but none that really satisfies me in terms of readability. can you guys give me some suggestions? I figured the best way would involve

myList.retainAll()

somehow but i couldnt find a good way to make use of it

What is the ideomatic way to perform automatic dependency injection in functional Kotlin code? At the moment, most of my code is very java-like where it contains bunch of classes that contain business logic and dependencies between those classes are resolved with Dagger's constructor injection. Top level functions are mostly used as utility functions. This works fine, but it seems like Kotlin promotes a pattern where code is instead moved from classes into top level functions that cannot have dependencies easily injected (without passing everything manually of course). One practical example is with coroutines. Convention dictates that functions launching new coroutines should be declared as extension functions of

CoroutineScope

. This practically requires such functions to reside on top level, since calling member extension functions of other classes is very awkward in Kotlin. But on the other hand, I fail to see how to properly handle dependencies in top level functions. * For example if I have

Downloader

class that has

CoroutineScope.startDownloading

method, I can inject every dependency of the downloader easily via constructor, but calling

startDownloading()

is awkward (I need to call it via

with (downloader) {startDownloading())

statement). * On the other hand, if I just create

CoroutineScope.startDownloading()

top level method, it would be easy to call, but I would have to provide dependencies with every single call to that method, which would create messy code.

Anyone got experience packaging an executable fat jar file with kotlin using gradle? Most resources I have found seem to be pointing toward doing like in this post https://medium.com/@preslavrachev/kotlin-basics-create-executable-kotlin-jars-using-gradle-d17e9a8384b9 But I still get the `NoClassDefFoundError: kotlin/jvm/internal/Intrinsics`even though I've done like that

i created an string extension function like so:

fun String.resourceContent() : String = javaClass.getResource(this).readText()

if i call

"/token.json".resourceContent()

in the test i get null if i call

javaClass.getResource("/token.json")

in the test it works why does this not work in an extension function?

Hello~

infix fun <A, B, C> Pair<A, B>.to(that:C) = Triple(this.first, this.second, that)

You can still use a factory method in case you need validation. Letting the data class validate it's content makes sense. Like EmailAddress.parse and then make the constructor private. @ursus

https://pl.kotl.in/zXrGRcejU seems like a weird bug with nullable generics. Try running it, then remove

reified

from the function header and run again

@Pablo Schmid are you returning something out of it, or otherwise doing something that requires it to be exhaustive?

Right?

I don't think this is possible without an extra param in

genericBuilder

, but I don't know all the things.

class GenericClass<T> {
    var property: T? = null

    fun genericBuilder(builder: T.() -> Unit) {
        // how to initialize T?
        property?.builder()
    }
}

i wanna do this thing

Hi guys, I'm facing a dilemma and I need your advice. Which one of these two lines you think is better:

val parsedValue = if (propertyValue is String) propertyValue.toDouble() else propertyValue as Double

VS

val parsedValue = (propertyValue as? String)?.toDouble() ?: propertyValue as Double

Hi, is there anybody who are using ktor for REST API and has experience in writing IT tests with mocks? Lets assume that I use a kind of service class in my routing. I need to mock that service and test concrete routing / endpoint

guys what is the most important thing to do when go to interview as android developer ?!

I have some raw bytes (byteChannel / byteArray/byteReadPacket) and want to compress/decompress it (standard DEFLATE). Any sugestions?

i have a line:

if (header?.startsWith("Basic ") != true) throw Exception

. intellij is suggesting i replace this with

require(header?.startsWith("Basic ") == true)

, but if i do that,

header

is no longer smart cast

i don’t know but sometimes, by listening to what intellij tells you do to the code doesn’t compile anymore

Some thoughts from recent interview processes. Kotlin is the best language for interviews I could imagine. Even people unfamiliar with Kotlin can understand and so many things are trivial to implement.

I'm getting a NPE on this lines? Any ideas how that can happen?

What is the idiomatic way in Kotlin of a doing a "mapping" of one object into another one. e.g. from

User(firstName: String, lastName: String, age: Int)

to

UserEntity(name: String, age: Int)

. I found that using a scope function is very useful but I don't know which would be the best. The pros and cons are as follows: •

let

seems as natural choice since it returns lambda result but having to repeat

it

for every property feels a little redundant, e.g.

user.let { UserEntity(it.firstName + it.lastName, it.age)}

•

run

allows to eliminate

it

from the above example but

run

looks awkward as a mapping function, e.g.

user.run { UserEntity(firstName + lastName, age)}

•

with

also seems a viable option, e.g.

with(user) { UserEntity(firstName + lastName, age)}

but I'm not sure if this is intended usage of

with

function, in Kotlin docs it is described as a function which lambda result should not be returned or as way to introduce a helper object (https://kotlinlang.org/docs/reference/scope-functions.html), so I'm not sure

I've got a small little 24 lines of kotlin code that just queries java to get properties like version. Yet for some reason the jar that gets produced is 35MB in size. At the same time, the actual intelliJ project is only 9KB in size... this cannot be right, I use only native packages no imports, simple code, WTF is going on here?

package org.ppp.installer

object JavaGetProperty {
    @JvmStatic
    fun main(args: Array<String>) {
        try {
            val property = args.getOrNull(0)
            var propertyVal: String

            if (property == "java_patch") {
                //Custom Properties
                val fullVersion = System.getProperty("java.version", "unknown")
                propertyVal = fullVersion.split("_")[1]
            } else {
                //Direct Unprocessed Properties
                propertyVal = if (property != null) System.getProperty(property, "unknown") else "unknown"
            }

            print(propertyVal.trim())
        } catch (e: Exception) {
            print("unknown")
        }
    }
}

has anyone heard of a library that provides a delegated property for constructing things in JUnit’s setUp phase automatically? instead of:

private lateinit var dog: Dog

@Before fun setUp() {
  dog = Dog()
}

there would be:

private val dog by before { Dog() } // constructs `Dog` instance once per test

Is it safe to assume that collection transformation functions like

map

return Lists whose

get

method is O(1)? If so, is that documented?

Is there a way to instantiate an object while setting some properties on it? As an expression like:

val a = Some() { b = "value" }

Or do I need multiple lines for that

Swift has a funtionBuilder/propertyWrapper that’s pretty nifty. Does kotlin have something like this? Something like

@sumOnlyOddInts

above a list of ints would filter the ints.