👋 Hello, team!

Hi, I am a bit confused about Kotlin Coroutines Jobs. Is it the case that a job can only run once? I wanted to launch the

searchJob

every time my search parameter changed in the example below. What happens is that the

searchJob

is called successfully the first time I pass my parameter, but never again after that. Could someone please have a look ?

What Physics Engine could I use with Processing 4 ? I've seen that there are multiple Physics Engines in Java, very few in Kotlin, I've stumbled upon KPhysics which seems nice but is there anything else for the language ?

How do I get the string that was passed to the command line to start my JVM program?

Hey 👋 Is there a way to test/assert logged messages in a unit test (type DEBUG, message content)? Using "import mu.KotlinLogging" 👀

hey channel … I’m Java developer and newcomer with Kotlin. I’ve been working on a Kotlin/Springboot and Kafka application. I am using the KafkaListener and it requires a

const val

for name of the topic. This information comes from a parameter. Even if I assign the value to a new variable I get this issue… Could you please help me to implement that correctly?

hey channel. I’ve worked with Spring Open Feign with Java but know I want to do the same with Kotlin. Please, is there someone here with a good boilerplate? I mean.. without this kind of issue.

Hey Channel! How does one convert a Map<String, Any?> to data class? I’m trying to convert a

Map<String, Any?>

to a data class object using Kotlinx Serialisation. The Data Classes:

import kotlinx.serialization.Serializable

@Serializable
data class Person(
    val uuid: String,
    val age: Int,
    val name: String,
    val address: Address
)

@Serializable
data class Address(
    val street: String,
    val city: String,
    val zip: Int
)

This is the function I use to convert to data class.

import kotlinx.serialization.json.decodeFromJsonElement
import kotlinx.serialization.json.encodeToJsonElement
import kotlinx.serialization.json.jsonObject
import kotlinx.serialization.json.Json

internal inline fun <reified T : Any> Map<String, Any?>.toPojo(): T {
    val JSON = Json { encodeDefaults = true }
    val jsonObject = JSON.encodeToJsonElement(this).jsonObject
    return JSON.decodeFromJsonElement<T>(jsonObject)
}

Here’s the function call:

val map = mapOf(
    "uuid" to "agsdjhdg",
    "age" to 26,
    "name" to "Aseem",
    "address" to mapOf(
        "city" to "Chennai",
        "street" to "street1"
    )
)

println(map.toPojo<Person>())

I get the following error:

Exception in thread "main" kotlinx.serialization.SerializationException: Serializer for class 'Any' is not found.
Mark the class as @Serializable or provide the serializer explicitly.
	at kotlinx.serialization.internal.Platform_commonKt.serializerNotRegistered(Platform.common.kt:91)
	at kotlinx.serialization.internal.PlatformKt.platformSpecificSerializerNotRegistered(Platform.kt:29)
	at kotlinx.serialization.SerializersKt__SerializersKt.serializer(Serializers.kt:60)
	at kotlinx.serialization.SerializersKt.serializer(Unknown Source)
	at kotlinx.serialization.SerializersKt__SerializersKt.serializersForParameters(Serializers.kt:117)
	at kotlinx.serialization.SerializersKt.serializersForParameters(Unknown Source)
	at kotlinx.serialization.SerializersKt__SerializersKt.serializerByKTypeImpl$SerializersKt__SerializersKt(Serializers.kt:99)
	at kotlinx.serialization.SerializersKt__SerializersKt.serializer(Serializers.kt:59)
	at kotlinx.serialization.SerializersKt.serializer(Unknown Source)
	at MainKt.main(Main.kt:98)

How does one convert a Map<String, Any?> to data class? Thanks in advance!

Still no blog post about 1.8.0 release?

Hello, please help, I deployed ktor project to docker using this

Dockerfile

but when I try to upload image and read file I’m getting error of

file or directory not found

BUT in reality the directory exist or file do exist

Learning data structures in kotlin and was curious if/why there wasn't a LinkedList impl in kotlin. Anyone know what

@elizarov

was talking about here that itd be "harmful" to have it?

I guess there wasn't, but maybe it is possible now? For me I'd like to suppress `MayBeConstant`and use only `val`s

Hi Folks, I am new to Kotlin and having trouble dealing with enums and if someone can help please, line no. 49 in mentioned screenshot is giving me undefined and line number 48 is working fine, list which is defined inside enum seems to work fine and other one which is defined outside shows undefined, I just want to define list outside enums.

Easy question. There is

.forEach()

on

Iterator

but not

.map()

. What is the right way to map over an iterator?

I've got a somewhat unusual use case that I'd appreciate any input on. I've got an Android app storing data in SQLite using Android's Room persistence library, but for troubleshooting purposes, I have a system to export the database file so that I can look at it on my desktop and do analysis on the contents. Room is an Android-specific thing, so I can't reuse any of the Room data modelling for a pure JVM program running on the desktop. Ideally I'd really just like to run some basic SQL queries on the database without modifying it. Really just the type-safe equivalent of firing up the sqlite client and running some queries. Can I do that without too much effort if I use an ORM-focused library like SQLDelight or Ktorm, or would I have to model everything in the ORM to make that work? (There are also some migrations between versions, mostly in tables I'm not interested in, and I'd prefer to not have to create those if I can avoid it)

Hi Folks. I have a maven multi-module project and all of them are Kotlin. Now I want to use Lombok in one of the modules to make the module easier to use in another java project. I already read this https://kotlinlang.org/docs/lombok.html and followed the steps, but the compiled classes don’t contain the generated code from Lombok.

mvn clean package

output, Kotlin file and generated class file, as well as the pom file, can be found here Any help is highly appreciated 🙂

if I’m doing:

when (string){

    "SomeString" -> { }
}

can i have it somewhere set to ignore case when matching?

Correct me if I am wrong: the Kotlin compiler was originally written in Java. Meaning, a Java program

J

was written to parse the AST of a KT file(s) (the first Kotlin compiler, written in Java) and produce an executable/binary. Program

J

(the binary that Java produced from source code

J

) was then used to compile a Kotlin program

K

that itself could read KT files (the second Kotlin compiler, written in Kotlin) and produce a binary. The binary produced from

K

was used to compile an iteratively better version

K1

, which was used to compile

K2

, etc. Somewhat based on this. Does the current compiler rely on the JVM to run?

Hey I was wondering if it was possible to put properties on a class via annotation? Example being

annotation class Example(val a: String)

@Example("t")
class Foo() 
// to
@Example("t")
class Foo(val: a = "t")

I have a question regrading `Grouping.fold`: I assumed the following 2 calls to return the same value, but the second returns

{a=[1, 3, 4, 5], b=[1, 3, 4, 5]}

instead of the expected

{a=[1, 3, 5], b=[4]}

. Looks the 2nd variant re-uses the initial value for all groups. What is a good use case for the 2nd variant?

val g = listOf("a" to listOf(1, 3), "b" to listOf(4), "a" to listOf(5)).groupingBy { it.first }
g.fold({ _, _ -> mutableListOf<Int>() }, { _, acc, item -> acc.addAll(item.second); acc })
g.fold(mutableListOf<Int>(), { acc, item -> acc.addAll(item.second); acc })

is

return@

considered harmful or unidiomatic? for example, I want to make a function that sums up the number of values of a list, or returns

null

if a certain value is detected. I wrote it as

fun List<Foo>.calcSum() = this.fold(0) { sum, val -> if (something) { sum + val } else { return@calcSum null } }

is this bad style? I had to add a type hint for the function to even compile.

hey team. I am noob with Kotlin and I am looking for a good way to call Spring OpenFeign. I shared a screenshot of how I am thinking to do, but the IDE is suggesting to use that

lateinit

… should I? In java I would inject the interface like this

@Autowired MyFeignClient client

and I can use it just like this

client.postMyData()

but please, how can I do this in Kotlin?

is there any way to express this

plus

overload with Kotlin pattern matching?

sealed class MyType {
    data class A(val amount: Int) : MyType()
    object B : MyType()

    operator fun plus(rhs: MyType) =
        when (this to rhs) {
            (A, B), (B, A) -> { B }
            (A, A) -> { A(this.amount + rhs.amount) }
        }
}

note, I’m aware that I can turn this into an

if

/`else` :

operator fun plus(rhs: MyType) =
    if (this is B || rhs is B) {
        B
    } else {
        val lhsAmount = (this as A).amount
        val rhsAmount = (rhs as A).amount
        A(lhsAmount + rhsAmount)
    }

When a suspend function calls another, is there an assurance of the order of operations and whether they are synchronous or not? Will this always print A-B-C regardless of under which conditions x is invoked?

suspend fun x() {
  print("A")
  y()
  print("C")
}
suspend fun y() {
  print("B")
}

has anyone worked on login using google and able to generate jwt tokens after successful login? if yes please help me i want to use login using google functionality in my project. Using micronaut framework.

Hey I am really interested in studying the source code, but I am finding it very laborious to grasp what's going on by just reading the source at https://github.com/JetBrains/kotlin . I can understand the concepts like IRs, parsing, ..., but I don't grasp the folder structures, filenames and ideas regarding encapsulation. Any ideas on how to proceed? TBH I'm finding it odd how such code can get into big corp's stack, but maybe I'm misled by its organization.

What's the nicest and most efficient way to take two lists, one of

data class Foo(val id: String, ...)

and one of

data class Baz(val id: String, ...)

and output a map of the id against a pair of Foo and Baz that correspond

Map<String, Pair<Foo?, Baz?>>

where either could not exist?

BTW do you know how serious Google's push of Kotlin to Android is? To me it seemed like Java is being deprecated totally, but is it this way or dual APIs?

To me it seemed like Java is being depreceated totally, but is it this way or dual APIs?

Is there a way to check if a lazy variable has been initialized? Some sort of equivalent to lateinit’s

::something.isInitialized

?