Lets say I have a factory that retrieves an instance of a model based on a reference. Lets say I have a bunch of values I need to either: Store into a new class if its reference does not exist, or modify on an existing one if it does exist. Now I need to constantly redeclare the mandatory fields in every single one of my models.

fun main(){
    val f1: Int = 3
    val f2: String = "foo"
    val f3: Double = 23.2
    val f4: String = "bar"
    val f5: String? = "rez"
    val f6: String? = null

    val model = DBModelRepository.getByField1(f1)
        ?.apply {
            field2 = f2     //need to doubly write all these mandatory fields
            field3 = f3     //
            field4 = f4     //
        } ?: DBModel(
            field1 = f1,    //
            field2 = f2,    //
            field3 = f3,    //
            field4 = f4,    //can become a big hassle when its 15+ fields
        )
    model.apply {
        field5 = f5         //I can at least save a bit of hassle by doing the optional fields after both cases
        field6 = f6
    }
    DBModelRepository.save(model)
}

class DBModel(
    val field1: Int,
    var field2: String,
    var field3: Double,
    var field4: String,
    var field5: String? = null,
    var field6: String? = null
)

object DBModelRepository{
    fun getByField1(field1: Int) : DBModel? {
        TODO()
    }
    fun save(dbMobel: DBModel){}
}

Now is this a relatively "small example" with 4 fields, but we're working with a lot of pretty big models. Sometimes its a bit harder than just "updating" a model like the example and we need to redo this logic in other places. Is there a better way to do this?

Hello everyone. I’d like to use Kotlin for a back end. Would you recommend Spring or Ktor ? and What is the orm for Spring ?

Hi everyone, new to the channel, I’m a founder of a new startup being built in Scotland https://www.locovo.co/contact.html, I’m developing the backend in Kotlin rather than Java as I always found the java language overly complex

Hi, I've set up breakpoints for debugging, but it ignores them and flies right through. Any advice?

Is there some canonical library if I need a JSONRPC2 client in Kotlin? There are a few small projects, most with barely any stars on GitHub https://github.com/Reedyuk/jsonrpc-kotlin-client, or other larger projects that seem outdated, and e.g. don't have documentation anymore because the wiki link is broken https://github.com/markaren/YAJ-RPC

In the first peace of code, it said that the

throw

is unreachable. But after I removed it there is an compile error. Is it a known issue?

sorry, in the above code, block is non-null, but when I use

addparagraph("") it requires the {}

is there a way around that?

Hi I need to convert a function with java pattern class to kotlin regex class but my functions not returning the same output (

matchesList

) Code With Pattern Class

val matcher = pattern.matcher(string)
val matchesList = mutableListOf<String>()
while (matcher.find()) {
    matchesList.add(matcher.group(0))
    if (!isGlobal) {
        var i : Int = 1
        val iEnd : Int = matcher.groupCount()
        while (i <= iEnd) {
            matchesList.add(matcher.group(i))
            i++
        }
    }
}
return matchesList

Code With Regex Class (not working)

var result : MatchResult? = regex.matchEntire(string) ?: return mutableListOf()
val matchesList = mutableListOf<String>()
while(result!=null){
    result.groups[0]?.value?.let { matchesList.add(it) }
    if(!isGlobal){
        var i = 1
        while(i <= result.groups.size){
            result.groups[i]?.value?.let { matchesList.add(it) }
            i++
        }
    }
    result = result.next()
}
return matchesList

Hi, I am trying to compose my domain model for my new project and use value classes at some places. I have run into the problem that annotations from the value class attributes are lost at runtime.

class Test(

    @field:Valid
	val inlinedMember: InlinedMember,

	@field:Valid
	val normalMember: NormalMember,
)

@JvmInline
value class InlinedMember constructor(
	@field:NotBlank
	val subAttr: String
)

class NormalMember constructor(
	@field:NotBlank
	val subAttr: String
)

After I compile this code and run it, the property inlinedMember of the class Test is replaces with the type String and the annotation @field:NotBlank is lost, resulting in the validator not validating this constrain. Has anyone an idea how to keep the information (without copying it) or what else to do? The goal is to use the same value class (e.g. email, bithdate, username,..) at several places and only define the constrains once. This is a spring boot project, using jackson to parse and validate the JSON data on the REST controller

Is there a way to make reading Kotlin docs more reader-friendly? For example, it would be nice if there would faster way to find a function or property than either scrolling down or using find (i.e. CMD+F). I’ve always like the Android Docs approach where you can choose between the “On this page” section on the right, and “Summary” section. Screenshot source: https://developer.android.com/reference/android/content/SharedPreferences

I'm developing with MongoDB and I'm creating a common class for the connection to DB. I was having trouble implementing getCollection() generic method but I succeeded. I'm looking for advice or alternatives to my approach. GetCollection() Method:

inline fun <reified T> getCollection(collection: String): MongoCollection<T> {
  return database.getCollection(collection, T::class.java)
}

Full Code:

open class Connection<T> {
  constructor(){
    startMongoDB()
  }

  val client by lazy { KMongo.createClient()  }
  val database by lazy { getDB() }

  fun getDB(): MongoDatabase {
    return client.getDatabase(DB_NAME)
  }

  inline fun <reified T> getCollection(collection: String): MongoCollection<T> {
    return database.getCollection(collection, T::class.java)
  }

  private fun startMongoDB() {
    client
    database
  }
}

I have this code

val pdfDoc = PdfDocument(PdfWriter(fileName))

but the implementation for PdfDocument is

public PdfDocument(PdfWriter writer) {
        this(writer, new DocumentProperties());
    }

what is pdfDoc assigned to with no return value?

Is there a Kotlin-specific way to load a Kotlin class based on its fully qualified name and then call its default constructor?

Class.forName

+

Class.getConstructor

+

Constructor.newInstance

, but maybe something that starts with

KClass

?

When doing a method inference, can I somehow fix this?

I'm using kotlin 1.6.10. I thought it enforced exhaustive whens? I get this warning, but no error "Non exhaustive 'when' statements on enum will be prohibited in 1.7, add 'BLAH' branch or"

Is there a simpler form of

(x != null && y == null) || (x == null && y != null)

?

question, not sure about the right chan to post it so trying here: is there any data available about adoption for different kotlin versions? I’m thinking about removing 1.3.* support from a library i’m maintaining in order to simplify the code, but i’m not sure if it will cause issues to many users

Hello everyone I have a data class

import kotlinx.serialization.Serializable

@Serializable
data class MessageModel (val senderId : String, val channelId : String, val id : String, val contents : String, val date : Long)

And when I do this inside my (this is a multiplatform project) web app

console.log(message.date::class.simpleName )

The result is

Double

!! What is happening here? It's causing me runtime errors, as I need a long. This MessageModel I receive from my backend and the value of the date is epoch milis, and the value is

1641905913211

this is interpreted as double. But if I don't use the value of

message.date

and instead just directly input

1641905913211

it works, meaning the value isn't the issue, but for some reason when serializing it becomes a double? Not sure where to ask this, is this Multiplatform issue, Kotlin general issue?

const val kotlin = "1.6.10"
    const val kotlinxSerialization = "1.3.2"

Hi everyone, I hope this is an appropriate place to ask about the use of kotlin gradle (build.gradle.kts). Im having trouble moving from groovy to kotlin. I've put my original build.gradle and attempt at the new one https://gist.github.com/tyhdefu/0cdf5428be7699a8bb7ef7fa97e278b7

Is there a way to simplify this code or at least make it more beautiful ?

val List<Int>.minmaxDifference get() = maxOf { it } - minOf { it }
// chestRoom is a set, blockX/Y/Z are Int
// CHEST_ROOM_MIN_SIZE & MAX_SIZE are const val Int

if (chestRoom.map { it.blockX }.minmaxDifference in CHEST_ROOM_MIN_SIZE..CHEST_ROOM_MAX_SIZE) return false
if (chestRoom.map { it.blockY }.minmaxDifference in CHEST_ROOM_MIN_SIZE..CHEST_ROOM_MAX_SIZE) return false
if (chestRoom.map { it.blockZ }.minmaxDifference in CHEST_ROOM_MIN_SIZE..CHEST_ROOM_MAX_SIZE) return false

Hello I have extracted Kotlin class from

jar

file (from Android library

aar

), decompiled it and I see that this Kotlin class is missing Kotlin metadata (class is not annotated with

@Metadata

annotation). What could be the reason? The issue is that library user cannot use Kotlin related constructs like named arguments, so I wonder is there a setting or compiler flag to always add Kotlin metadata? 🤔 expected result in compiled class:

@Metadata(mv = {1, 6, 0}, k = 1, xi = 48, d1 = {"\000$\n\002\030\00"}..."})
public final class MyClass {
   ...
}

I want to delegate the interface implementation to an instance constructed using 

this

.

class ImplByInterface2(val a: Interface2): Interface1 {...}

class MyClass : Interface1, Interace2 {
    // Delegate Interface1 implementation to this
    private val impl: Interface1 = ImplByInterface2(this)

}

I found it not easy to use

by

. Is there any convenient way? Both language feature and IDE trick are welcomed. Edit: makes it clearer.

https://lambda.show/blog/introduction-to-monads Can someone explain to me the voodoo of how in step 2 the monad knows to return success or failure while the return type is neither of those, but the base class??

in `MemJogLib.kt`:

object MemJogLib {

    var testingOnlyChangeForTesting = false

    val BUILD_ROOT: String = File(".").canonicalPath

    private val MJL_BOOKS_DIR: String? = System.getenv("MJL_BOOKS_DIR")

    @JvmStatic
    fun getMjlBookDir(): String =
        if (testingOnlyChangeForTesting) {
            "$BUILD_ROOT/target/test-classes"
        } else {
            MJL_BOOKS_DIR!! // <= NullPointerException HERE
        }

At the start of all tests, I make sure I call initialized:

private val initialized: Boolean by lazy {
        testingOnlyChangeForTesting = true

With

testingOnlyChangeForTesting = true

, the second branch of the

if

statement shouldn't even be called! When I run my tests from Maven at command line on my desktop, everything works perfectly. Using command-line Maven on the build server, I get:

java.lang.ExceptionInInitializerError
	at com.goalqpc.memJogLib.TestGlobals$initialized$2.invoke(TestGlobals.kt:145)
	at com.goalqpc.memJogLib.TestGlobals$initialized$2.invoke(TestGlobals.kt:144)
	at kotlin.SynchronizedLazyImpl.getValue(LazyJVM.kt:74)
	at com.goalqpc.memJogLib.TestGlobals.getInitialized(TestGlobals.kt:144)
	at com.goalqpc.memJogLib.TestGlobals.testDbInMemory(TestGlobals.kt:220)
	at com.goalqpc.memJogLib.servlet.MjlServletHandlerTest.before(MjlServletHandlerTest.kt:44)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at org.junit.internal.runners.statements.RunBefores.invokeMethod(RunBefores.java:33)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:242)
	at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:137)
	at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:112)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:189)
	at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:165)
	at org.apache.maven.surefire.booter.ProviderFactory.invokeProvider(ProviderFactory.java:85)
	at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:115)
	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:75)

Caused by: java.lang.NullPointerException
	at com.goalqpc.memJogLib.MemJogLib.getMjlBookDir(MemJogLib.kt:66)
	at com.goalqpc.memJogLib.MemJogLib.<clinit>(MemJogLib.kt:72)
	... 39 more

Greetings everyone, my name is Itish and I am new to Kotlin Language, I was reading the Guidelines and Code Of Conduct for Kotlin Slack on the GitHub Repo. • There a channel has been mentioned, by the name, #kontributors Contributing to Kotlin. Unfortunately, I am unable to navigate to the channel...does the channel no longer exists? I will be thankful if someone could show me the way...😅

Hello everyone. My full name is Ernest N. Wilcox Jr. but I answer to Ernie. This is my first message, and I hope I'm not misusing it by introducing myself. Moderators, if this is too much, feel free to remove it - and please let me know. I will not be offended. I am a senior citizen, and I am attempting to learn the Kotlin programming language thanks to the generosity of the JetBrains Academy and HyperSkill-dot-org. I started using computers with the Commodore Vic 20, the Commodore64, then finally an IBM-clone PC powered by an Intel-8088 CPU, 64KB RAM, and a 100 MB MFM Hard Drive in the early 1990s. Around that time I made a hobby of learning a bit about Assembly language so I could build small .com utilities to add commands that did not exist in MS-DOS 3.1. I liked Assembly because the commands were direct and simple, not mysterious and unintelligible. I also attempted to learn a bit about GW-Basic, but most commands were too complicated. For example, there were hundreds of switches that could be used with the print command. It was used to print to the console, a file, or the printer (even if there was not one present - then the output simply got lost in the ether :)). Later, when I moved to Windows 95, I I attempted to learn Q-Basic. That language may have been better than GW-Basic, but documentation/language-specifications were nearly nonexistent. The only sources of information available to learners were hard-copy books that could be purchased from local book stores, and the good quality/most useful manuscripts were very expensive, so I lost interest. Now that I have retired (after raising my family), I once again have returned to attempting to learn a bit about computer programming. I have studied C, C++, C#, F#, Java, and now Kotlin. I also took a stab at Pascale for a while, but I could not find any online courses that I could afford. The reason I have finally settled on trying to learn Kotlin is I want to be able to build apps that can run on the Windows or Linux desktops as well as on my Android phone. I don't know what projects I want to build yet, but I am sure I will come up with a few by the time I learn enough. Back when that IBM-compatible PC suffered a head-crash, I was not able to find another HD - the MFM drives were no longer being built or sold. The technology was obsolete by then, so I embarked on learning to build my own PC. I purchased a copy of "Upgrading and Repairing PCs", and off I went. I discovered that it was not all that hard to do. Since that first 'home-brew' PC, I have built all the desktop PCs I have ever owned. I have purchased laptops because I have not been able to find any laptop cases usable for home-brew construction that are cost-effective enough to make such a project worth-while. My current desktop is a budget-gaming PC, although I am not a gamer. I just wanted to get better performance. The machine has an AMD Ryzen-5 Picasso CPU, 32 GB RAM (the mainboard supports up to 64 GB), an MSi X470 Gaming Plus MAX motherboard, a Gigabyte NVIDIA Ge-Force GT 1030 graphics adapter with 2 GB video RAM, a Samsung SSD 970 EVO Plus 1TB M.2 drive, and a Seagate 2TB hard drive. I got a new case with 4 RGB fans and a tempered-glass left-side door. The case is designed for good air-flow and has filtered input/output air vents, so the system maintains a CPU temperature range between 30 and 40 degrees Celsius most of the time. I dual-boot Windows 10 with KDE Neon GNU/Linux. I tried Windows 11 for a while, but mouse support is a bit flakey, so I clean installed Windows 10 again and I'll wait until Microsoft releases the next significant Windows 11 upgrade - probably this coming fall/winter (2022). I may find myself switching over to GNU/Linux entirely at some point, but for now I am happy dual-booting. Politically, I'm pretty much a liberal because I believe in the old adage "What's good for the Goose is good for the Gander." - in other words, if I have a right, everyone else should have that right too, and vice-versa. I believe that everyone is entitled to their opinion, but I also believe that opinions should be stated as such, and NOT be confused with facts. If you state something as a fact, cite the source of your supporting information. If you state an opinion, make it clear that you are doing so by prefacing it with a phase similar in meaning to "I believe . . . ". That's it. This is pretty much me. I look forward to future conversations although I'll try to be a bit less talkative. Ernie

Hi everyone \o I was currently getting started with Kotlin and I wanted to ask. How is a project structured? What is the standard way of structuring a Kotlin project? I don't.. use JetBrains IDEs as a daily driver (Although I am excitedly waiting for Fleet to launch!) and trying out Kotlin has been a bit of a pain for me personally. Opening the "getting started" webpage immediately starts pushing IntelliJ IDEA which I don't want to use 😛

Can this maybe be implemented? Or are there other solutions which may be easier to implement?

Hi all, I'm learning Kotlin + Ktor + Graphql by following this tutorial. However, when I run the server and visit http://localhost:8080/graphql I do not see the graphql playground 🤔 Here's what I did so far: • created the project using the project builder on ktor.io • added the kgraphql_version in gradle.properties • updated the build.gradle.kts with the line mentioned in the tutorial • in the tutorial

src/Application.kt

is mentioned but my automatically generated

Application.kt

file is under

src/main/kotlin/com.ryanzidago/Application.kt

🤔 Here's the content of my

Application.kt

package com.ryanzidago

import io.ktor.server.engine.*
import io.ktor.server.netty.*
import com.ryanzidago.plugins.*

import io.ktor.application.Application
import io.ktor.application.install
import com.apurebase.kgraphql.GraphQL

fun main() {
    embeddedServer(Netty, port = 8080, host = "0.0.0.0") {
        configureRouting()
    }.start(wait = true)
}
fun Application.module(testing: Boolean = false) {
    install(GraphQL) {
        playground = true
        schema {
            query("hello") {
                resolver { -> "World" }
            }
        }
    }
}

Intellij tells me that there is a problem with the

install

(Not enough information to infer type variable B) and

playground

(Variable expected) but I cannot figure out what is wrong 🤔 When I type

gradle --version

in my project root I get the following output:

ariviv 
❯ gradle --version

------------------------------------------------------------
Gradle 7.3.3
------------------------------------------------------------

Build time:   2021-12-22 12:37:54 UTC
Revision:     6f556c80f945dc54b50e0be633da6c62dbe8dc71

Kotlin:       1.5.31
Groovy:       3.0.9
Ant:          Apache Ant(TM) version 1.10.11 compiled on July 10 2021
JVM:          17.0.1 (Oracle Corporation 17.0.1+12-39)
OS:           Linux 5.4.0-94-generic amd64

Any tips?