kotlinlang #getting-started

Is this the right place to ask something about Jetbrain's Compose for desktop? I just started using it and columns seem to be scrollable always and even scroll away components that are not in the column. If the column is is another column or in a box then sibling composables above and below it also scroll. Is this normal behavior?

Ankit Shah

12/22/2021, 5:15 PM

Hello everyone, just a small question. In kotlin lets say I do,

(10/3).toInt()

it returns 3 but what I want is the upper value i.e. 4. How can I achieve it?

Filipe Duarte

12/23/2021, 5:58 PM

I updated kotlin and IntelliJ, and when I tried to execute a specific .kt file that contained the main function, it was impossible because it says that I was trying to overload the main function. I always used main functions alongside specific kotlin files in the same project. Maybe it was the Gradle.. I don’t know what to do

Josh Horwitz

12/24/2021, 1:44 AM

Hey all! Quick question, what is the best up to date book as far as learning kotlin as an experienced dev currently?

Glen

12/24/2021, 1:46 PM

Hello here. I have updated my Kotlin to 1.6.0 and when compiling some Kotlin code I get a warning and I don't know how to solve it.

Chetan Tuteja

12/27/2021, 7:19 AM

Hi guys! Quick question. Let us say I have a string array and I have another variable and I am just checking if that variable is in the array. I can directly use the

in

check for that. Is there any way to do the same check while ignoring case check? I know I can do the

any

check, anything besides that?

val abc = "abc"
val random = arrayOf("ABC", "egf")

val isThere = abc in random // Prints false

Mendess

12/27/2021, 1:07 PM

where is the documentation on what characters are allowed in a function name with backticks? I can't find any

Grian

12/28/2021, 5:55 AM

Does anyone know if it's possible to create a DSL like this:

myDsl { 
    1,
    2,
    3,
}

and end up with like a list of

1, 2, 3

somewhere in the DSL's code

🇳🇴 2

asavio

12/28/2021, 8:59 AM

Hey guys, Does anyone know a mechanism to sort a possibly infinite

Sequence

or one with a really a large count of objects lazily without it being too time consuming like the factory methods?

hfhbd

12/28/2021, 4:05 PM

How can you check, if a class has an initializer for a lateinit variable, when this class is passed as variable to another class?

class Config {
    lateinit var s: String
}
class Consumer(val config: Config) {
    init {
         require(config::s.isInitialized)
    }
}

My current workaround is using an internal member function:

fun isInitialized() = ::s.isInitialized

and call this function in

require

JonasDaWi

12/28/2021, 5:07 PM

Does anyone know how I can make a httpmethod=SEARCH request in ktor? In curl it works like this: curl host -X SEARCH

Eivind

12/29/2021, 9:03 AM

Hi, I have a data class named

Error

that I want to use to represents errors occuring in my api (not exceptions, but state different than what the user expected when they made their request). When I use it now Kotlin defaults to the java.lang.Error. Can I change this default, or should I pick a different name?

David W

12/29/2021, 8:38 PM

I have an inline function that takes a

List<Lock>

and an anonymous function. It needs to lock all of the locks, execute the function, and then unlock all locks. The anonymous function should also allow non-local returns. I've been banging my head against this for hours, anyone have a solution?

inline fun <T> write(locks: List<ReentrantReadWriteLock>, action: () -> T): T

mcpiroman

12/31/2021, 3:18 PM

I have the following pattern:

abstract class Base<T : Any>(val clazz: KClass<T>)

class Foo; class Bar;
object A : Base<Foo>(Foo::class) { ... }
object B : Base<Bar>(Bar::class) { ... }

Can I somehow 'reifine' the `T`paramater so I only have to write the parameter class once, e.g. `Base<Foo>()`or

Base(Foo::class)

? Edit: OK, it's fine that it's possible but I actually meant to ask 'how' to do that. The 2 ways I suggested above do not compile, nor can I use `reified`modifier.

:yes: 2

MisileLab

01/01/2022, 7:48 AM

How change sequence element?

James Whitehead

01/01/2022, 7:36 PM

Hi 👋 • What is the correct way to write a function signature using generics, whereby the first parameter is something like

<T>

and the second parameter is "an instance or implementation of T"? • Also kind of related question: When should one use

<T>

<T : Any>

, I'm not really sure what the difference is? Thanks in advance 🙂

Ayfri

01/02/2022, 5:11 AM

Hi ! Is there any way to force Tree Shaking in Kotlin/JVM ? I have this really simple code

private inline fun execute(block: () -> Unit) = block()

fun main() {
	execute { println("test") }
}

But when I see the Bytecode, it creates an

execute

static method on the MainKt class but never use it, is there a way to say to the compiler to not generate this method and just inline ?

hfhbd

01/02/2022, 10:54 AM

If you write a library and want to provide 1! useful test function, where do you store this function? In the main source with a comment, in the main source with an extra annotation like

TestingOnly

, or do you really create a new module containing only 1 function and publish it?

Rob Elliot

01/02/2022, 11:42 AM

Any recommendations for a library that can do string escaping, other than

org.apache.commons.text.StringEscapeUtils

Pablo

01/02/2022, 12:59 PM

How can I create a Map (it that's the best way) of having something for instance : 400 to CustomExceptionFor400 500 to CustomExceptionFor500 The first param is an Int and it's a HttpStatusCode, and the value is something like this

sealed class OrganizationExceptions : Exception() {
    object OrganizationNotFound : OrganizationExceptions()
    object ListNotAvailable : OrganizationExceptions()
}

This is an example, but it won't be always "OrganizationExceptions" I'm creating a method generic, also I don't know if it's better to create a sealed class or create

class OrganizationNotFoundException : Throwable() //or Exception()
class ListNotAvailable : Throwable() //or Exception()

Any recomendations? the method signature is :

fun apiCallWithStatusCode(codes : HashMap<Int, Throwable>, apiCall : suspend () -> Response<T>,){...}

sorianog

01/03/2022, 2:50 PM

I’m reviewing my Leetcode Java submissions and thought, I’d see what the code would look like with the Automagic to Kotlin conversion from Studio. One problem that I solved with updated Kotlin code seems to be less performant (by Leetcode benchmarking) 🤔 Maybe I’m not hitting their servers at the right time 😛 https://leetcode.com/problems/move-zeroes/discuss/1664500/Java-to-Kotlin-Converted-Solution%3A-Less-Performant-with-Kotlin

glenkpeterson

01/03/2022, 10:43 PM

Why isn't my JVM Double variable the same as itself in 1.6.10?

val dotOne: Double = "0.1".toDouble()
        assertSame(dotOne, dotOne)

expected: java.lang.Double@76774d21<0.1> but was: java.lang.Double@68be905c<0.1>

I understand that

assertSame

uses referential equality (checks that the parameters have the same virtual memory address) and should function like the

===

operator.

0.1 !== 0.1

because they are primitives and could be boxed to different objects before being compared for referential equality. But, when I declare a variable, I would expect it to have the same virtual memory address as itself. Be referentially (and structurally) equivalent to itself. Can I declare my variable somehow to not be compiled away to two different primitives that happen to have different virtual memory addresses?

dave08

01/04/2022, 12:20 PM

Will using this (with the `as`s, componentX and type params) get the array boxed?

@JvmInline
value class MethodParams1<A1>(val value: Array<Any?>) {
  
    operator fun component1() = value[0] as A1
    var arg1: A1
        get() = value[0] as A1
        set(value) { this.value[0] = value }
}

Colton Idle

01/05/2022, 5:10 AM

I wrote two extension functions that take different Types in the List type generic, but I get an error saying that I can't do that

private fun List<NetworkFoo>.mapToDomain(): List<DomainFoo> {
  return this.map { //stuff }
}

and

private fun List<NetworkBar>.mapToDomain(): List<DomainBar> {
  return this.map { //stuff }
}

Error

Platform declaration clash: The following declarations have the same JVM signature

I suppose the error message is helpful in giving me a hint that these two methods are identical in JVM land? If I use the auto-correct option I get

@JvmName("mapToDomaincom.network.model.NetworkBar")

but the annotation gives me an error of:

Illegal JVM name

Simon Lin

01/05/2022, 6:58 AM

How can I add element in specified index and if the index exist element, replace it.

val list = mutableListOf<String>()

list.add(0, "a")
list.add(0, "b")

list.toString() // except [b], actual [b, a]

Jason5lee

01/05/2022, 12:25 PM

I’m building a string with some logics, like

"something${somelogic}something${somelogic}"

. But it ends up being too long for a line. Any tips to rewrite to make the line shorter but still being conscious of how the string is built?

Jasin Colegrove

01/05/2022, 12:39 PM

Does anyone have any advice on printing documents from a kotlin desktop app? I need to be able to create printable documents from database data. I've looked at PDFBox (create PDF's that can later be printed) but I really want a clean idiomatic kotlin way of doing it?

Liudvikas Sablauskas

01/05/2022, 1:10 PM

Hello everyone. This is not really a question for #getting-started, but I couldn't find a better place (if there is, tell me). 3 years ago I held an internal company contest with 7 Kotlin edge case / oddity puzzles. Today we decided to revisit and solve them. We solved all except one. Can someone help us crack this nut?

/**
 * Task: Make line `DisNonNullable.nonNull()` not compile
 * Clarification: `DisNonNullable.nonNull()` will always have a non-null value, so it makes sense to not allow that method
 * Clarification: Everything else has to compile just as before, only `DisNonNullable.nonNull()` should fail
 * Clarification: The non-generic parameter type String is chosen only as an example. This hardcoded type is not the focus of the task
 * Restrictions: Mustn't modify main() method, DisNullable and DisNotNullable classes
 */

fun main(args: Array<String>) {
    DisNullable.nonNull()
    DisNonNullable.nonNull()
}

abstract class GenericMapper<T>  {
    abstract fun map(string: String): T

    fun nonNull(): GenericMapper<T> {
        val delegate = this
        return object : GenericMapper<T>() {
            override fun map(string: String): T {
                return delegate.map(string)
            }
        }
    }
}

object DisNullable : GenericMapper<String?>() {
    override fun map(string: String) = string
}

object DisNonNullable : GenericMapper<String>() {
    override fun map(string: String) = string
}

Title

Liudvikas Sablauskas

01/05/2022, 1:10 PM

/**
 * Task: Make line `DisNonNullable.nonNull()` not compile
 * Clarification: `DisNonNullable.nonNull()` will always have a non-null value, so it makes sense to not allow that method
 * Clarification: Everything else has to compile just as before, only `DisNonNullable.nonNull()` should fail
 * Clarification: The non-generic parameter type String is chosen only as an example. This hardcoded type is not the focus of the task
 * Restrictions: Mustn't modify main() method, DisNullable and DisNotNullable classes
 */

fun main(args: Array<String>) {
    DisNullable.nonNull()
    DisNonNullable.nonNull()
}

abstract class GenericMapper<T>  {
    abstract fun map(string: String): T

    fun nonNull(): GenericMapper<T> {
        val delegate = this
        return object : GenericMapper<T>() {
            override fun map(string: String): T {
                return delegate.map(string)
            }
        }
    }
}

object DisNullable : GenericMapper<String?>() {
    override fun map(string: String) = string
}

object DisNonNullable : GenericMapper<String>() {
    override fun map(string: String) = string
}

Rob Elliot

01/05/2022, 1:23 PM

It breaks the rules, but this is what I'd do:

fun main(args: Array<String>) {
  DisNullable.nonNull()
  DisNonNullable.nonNull()
}

// Internal so that there are only two immediate subtypes, but it isn't sealed, so other subtypes of
// those immediate subtypes can be defined in other packages.
abstract class GenericMapper<T> internal constructor() {
  abstract fun map(string: String): T
}

abstract class NullableGenericMapper<T> : GenericMapper<T>()  {

  fun nonNull(): GenericMapper<T> {
    val delegate = this
    return object : GenericMapper<T>() {
      override fun map(string: String): T {
        return delegate.map(string)
      }
    }
  }
}

abstract class NonNullableGenericMapper<T : Any> : GenericMapper<T>()

object DisNullable : NullableGenericMapper<String?>() {
  override fun map(string: String) = string
}

object DisNonNullable : NonNullableGenericMapper<String>() {
  override fun map(string: String) = string
}

Hang on - don't think I understood the purpose of

fun nonNull()

when I wrote that. Guess in my version it should return

NonNullableGenericMapper

Liudvikas Sablauskas

01/05/2022, 1:39 PM

It's incorrect, DisNullable and DisNonNullable should extend the same class

But I definitely remember that there was a solution, exactly according to these rules

Rob Elliot

01/05/2022, 1:41 PM

They do. Just with an extra layer of inheritance in the middle.

Liudvikas Sablauskas

01/05/2022, 1:42 PM

And that is not allowed 😄

object DisNullable : GenericMapper<String?>() {
    override fun map(string: String) = string
}

object DisNonNullable : GenericMapper<String>() {
    override fun map(string: String) = string
}

This should not change at all

Rob Elliot

01/05/2022, 1:42 PM

Why?

Liudvikas Sablauskas

01/05/2022, 1:43 PM

This is a puzzle, of course in practice you wouldn't care either way 😄

Rob Elliot

01/05/2022, 1:44 PM

But even puzzles need to justify their requirements.

Particularly if they are puzzles without a known solution. It's one thing to say "The constraints may seem arbitrary, but they can be met" as an intellectual challenge. "The constraints are arbitrary and it may be impossible to meet them" is silly - why would anyone waste their time trying to meet arbitrary constraints that are impossible to meet?

Liudvikas Sablauskas

01/05/2022, 1:46 PM

"The constraints are arbitrary and it may be impossible to meet them

No, I just said that

But I definitely remember that there was a solution, exactly according to these rules

Rob Elliot

01/05/2022, 1:47 PM

Ah, missed that in the middle of the thread. Fair enough.

👍 2

FWIW though on the illegal version it is possible to constrain the nullable type to a non-nullable one:

abstract class NullableGenericMapper<E : Any> : GenericMapper<E?>() {
  fun nonNull(): NonNullableGenericMapper<E> = TODO()
}

object DisNullable : NullableGenericMapper<String>() {
  override fun map(string: String): String? = null
}

Jason5lee

01/05/2022, 2:34 PM

Clarification: `DisNonNullable.nonNull()` will always have a non-null value, so it makes sense to not allow that method

It does not make sense to me.

Rob Elliot

01/05/2022, 2:46 PM

I think the intention of

nonNull

is to transform a

GenericMapper<String?>

into a

GenericMapper<String>

so that when you call

map

on it you get back a

String

not a

String?

. So calling

GenericMapper<String>.nonNull()

is pointless - it would effectively return itself - and the idea is to make it not compile so that people don't accidentally call it.

Liudvikas Sablauskas

01/05/2022, 2:49 PM

Yes, you are correct, that's the reason

Rob Elliot

01/05/2022, 3:07 PM

It's trivial of course once you remember the existence of extension functions:

fun main(args: Array<String>) {
  DisNullable.nonNull()
  DisNonNullable.nonNull()
}

abstract class GenericMapper<T>  {
  abstract fun map(string: String): T
}

fun <T> GenericMapper<T?>.nonNull(): GenericMapper<T> {
  val delegate = this
  return object : GenericMapper<T>() {
    override fun map(string: String): T {
      return delegate.map(string) ?: TODO("handle null")
    }
  }
}

object DisNullable : GenericMapper<String?>() {
  override fun map(string: String) = string
}

object DisNonNullable : GenericMapper<String>() {
  override fun map(string: String) = string
}

❤️ 1

Liudvikas Sablauskas

01/05/2022, 3:25 PM

Wow, that's a nice solution and it's definitely valid! Though I still can't remember if that's also the solution that I used 3 years ago, but it very well might be. Thanks!

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