kotlinlang #getting-started

What's the easiest way to use Kotlin / JS for static front-end applications? Compose or any other framework ? I'm only just familiar with JS' syntax but have almost nil web experience :)

Yatin Shelke

02/27/2022, 12:10 AM

Hi, i am new to kotlin multiplatform. Started with this sample Build a Full Stack Web App with Kotlin Multiplatform, and was able to get it running. However, when i tried to generate a test for the get method in the example in Server.kt, i see that the imports in the generated test do not get resolved. What dependencies do i need to add to build.gradle.kts to get this working? Would be nice to write tests along with the code. See screenshot that shows imports in red.

Sean Proctor

02/27/2022, 10:23 AM

Is there a more concise way to write this:

val result = foo.method1()
    .let {
        if (condition) {
            it.method2()
        } else {
            it
        }
    }.method3()

Klitos Kyriacou

02/28/2022, 3:11 PM

Today I learned:

fun foo(args: IntArray) {
    val a = intArrayOf(*args)  // Creates a copy of args
    //val b = intArrayOf(args)  // Compile error
    val c = intArrayOf(elements = args)
}

To pass an array to a varargs parameter, we are supposed to use the spread operator

. But that creates a copy of the array, which you might not want to do if you are calling a pure function in a loop. You can't pass the array itself, but I learned that you can pass it if you use a named parameter! Where in the documentation does it say that? [Update: looking at the generated bytecode, the call

intArrayOf(elements = args)

also copies the array, and produces the same bytecode as using the spread operator.]

😲 2

Mark

03/01/2022, 2:30 AM

Which is the most appropriate way to convert:

val foos: List<Foo> = ...
foos.takeIf { it.isNotEmpty() }

to a function reference 1️⃣

foos.takeIf(List<Foo>::isNotEmpty)

2️⃣

foos.takeIf(List<*>::isNotEmpty)

3️⃣

foos.takeIf(Collection<Foo>::isNotEmpty)

4️⃣

foos.takeIf(Collection<*>::isNotEmpty)

5️⃣ leave it as a lambda

3️⃣ 1

5️⃣ 10

4️⃣ 1

1️⃣ 2

毛小川

03/01/2022, 9:08 AM

Hello! Does

.forEach{it->}

guarantee the original sequence during execution?

:yes: 2

Anthony Flores

03/01/2022, 4:49 PM

Hey, is there some way to check if a lazy variable is initialized without using reflections?

Timo Stark

03/01/2022, 7:25 PM

Hi Folks - I have a question and I am not sure whats the best palce to ask. I am working with Mockito tests and Kotlin and can't make my

given

stub working. Any Idea where to ask?

Anthony Flores

03/01/2022, 7:57 PM

Is it possible to accept a sequence of values and have a method that accepts them? Example:

(255, 255, 255, 255)toRGBA()

Turyin

03/02/2022, 11:27 AM

How do I join the fleet slack group?

:not-kotlin: 1

Phani Mahesh

03/02/2022, 12:13 PM

Is there a way to restrict usage of external functions in a dsl? I’m thinking about creating and exposing a dsl using which users can provide their own domain spec. Is there a way to restrict them from using non whitelisted imports or language features?

Rob Elliot

03/02/2022, 3:32 PM

Is there a way in the stdlib to reduce a bunch of

Result

instances into a single Result? I can write it myself but a shame to repeat it. I want roughly the following:

data class Foo(val a: String, val b: Int)

val resultA: Result<String> = TODO()
val resultB: Result<Int> = TODO()

val foo: Result<Foo> = reduce(resultA, resultB, ::Foo)

So the function would look something like:

fun <A, B, T> reduce(a: Result<A>, b: Result<B>, work: (A, B) -> T): Result<T>

But obviously it would need loads of overloads.

Michael Langford

03/02/2022, 5:01 PM

Conditional Compilation: I know if I have a large pile of isolated code, I can easily conditionally compile it via module. My context here is an a mobile device android app only. However, I want to remove a pervasively used function call throughout the app for release. Let's call it "PrintStuffWeMayNotWantPrintedIn Production(varargs:List<ValuableData>)". I don't want to inactivate it, but remove it. My app functions in a somewhat adversarial situation (a medical app, low risk, but does have pentesters and curious teens to work through). I wish to not leave these call sites throughout the app as a hook that is exploitable to easily gain a bunch of info with tools such as Frida. Would this plan work: Conditionally compile out the actual part that prints/logs via BuildConfig.DEBUG then use proguard to remove the actual statement calls too? Or do I need to inline the functions too? Or is there a more "kotlinesque" way to remove/elide all the PrintStuffWeMayNotWantPrinted() calls from the app using a feature I just can't find the name of? (I'd ask other places for Proguard tips re the above, but if there are kotlin specific caveats I should be reading about, I'm all over reading your feelings or specific reference doc on the topic or even years of developer forum debate. I just don't really see more than brief exchanges on this topic)

✅ 1

Mason M

03/02/2022, 9:19 PM

Is it possible to catch exceptions if they are not of a certain type?

Ayden

03/05/2022, 3:27 AM

Hello everyone. I encounter the error when using

JDK 17

and

Gradle 7.3.3/7.4

Unsupported class file major version 61

. I think the solution to resolve this is to downgrade the JDK version to 11 after searching through the internet. What should I do to resolve this issue if I insist to use JDK 17. I am using WSL2, with the following setup for my console application.

JDK: 17
Build System: Gradle Groovy
Target JVM version: 16

Daeyoung Kim

03/05/2022, 7:50 AM

I don’t know what was wrong. Anybody can explain this error?

:thread-please: 2

Chih Wei Lin

03/05/2022, 5:10 PM

How to solve the following problem more elegantly: Given a keyword list and a input data list. Iterate through input data list and if the item contains one of the keywords, put it together. (Sample data and my brute force way are in the thread)

althaf

03/08/2022, 12:08 PM

when(args.approvalType) {
    ApprovalType.MULTI_SELECT_BATCH_APPROVAL.ordinal,
    ApprovalType.MULTI_SELECT_SINGLE_APPROVAL.ordinal -> {
        context?.apply {
            bgView.setBackgroundColor(getColor(R.color.sc_palette_green))
            subTitleTextView.text = getString(R.string.approvalSuccessLabelText)
        }
    }
    ApprovalType.MULTI_SELECT_SINGLE_APPROVAL.ordinal,
    ApprovalType.MULTI_SELECT_SINGLE_REJECT.ordinal -> {
        //TODO move to string resource
        titleLineTitleTextView.text = "List of Transactions"
    }
    ApprovalType.MULTI_SELECT_BATCH_APPROVAL.ordinal,
    ApprovalType.MULTI_SELECT_BATCH_REJECT.ordinal -> {
        //TODO move to string resource
        titleLineTitleTextView.text = "List of Batches"
    }
    ApprovalType.MULTI_SELECT_SINGLE_REJECT.ordinal,
    ApprovalType.MULTI_SELECT_BATCH_REJECT.ordinal -> {
        context?.apply {
            subTitleTextView.text = getString(R.string.rejectSuccessLabelText)
            bgView.setBackgroundColor(getColor(R.color.sc_palette_dark_blue))
        }
    }
}

Is this possible with when() to match two different blocks at the same time ? Here i need to match multiple blocks are the same time, in different context, to show the text "List of Transactions" and "List of Batches"

LastExceed

03/08/2022, 7:29 PM

is there a good way to associate something with a type in a way it can be generically looked up, but without each instance of the type holding a copy ? e.g. consider an abstract parent class

Animal

and some inheriting classes

Dog

Cat

etc, and i want each type of animal to have a

lifeExpectancy

. now of course i could just create

abstract val lifeExpectancy: Float

inside

Animal

and have each child class override that, but that would result in every instance of

Dog

holding a copy of the same number, which seems a bit redundant. (yes i know the overhead in this example is insignificant, but the problem is scalable). alternatively i could put the lifeExpectancy in the companion object, but then i can't generically look it up as the companion object can't be accessed generically (or at least i wouldn't know how to do that). i could store a reference to the companion object (or just the data i want to associate with the type in case it's not a primitive) in each instance to keep the overhead insignificantly low, but that would be incredibly ugly is there any way to do this more elegantly?

Trevor Hackman

03/08/2022, 10:06 PM

Hi, I was interested in suggesting a new standard library function in kotlin.collections and in writing it myself and making a pull request to contribute, Is this something that would be of interest? I found myself wanting this function but it not existing in the standard library, it would be

binarySearchIndexed

With a signature of perhaps

fun <T : Comparable<T>> List<T>.binarySearchIndexed(
    fromIndex: Int = 0,
    toIndex: Int = size,
    comparison: (T, Int) -> Int,
): Int

allan.conda

03/09/2022, 1:29 AM

Would it be bad practice to always override toString() to be the underlying value of an inline class? I'm not sure there's benefit to representing it as the boxed type by default. Asking because I recently made a mistake calling toString instead of the underk value

Marko Novakovic

03/10/2022, 1:13 PM

private fun UserContact?.isValid(): Boolean {
    contract {
        returns(true) implies (this@isValid != null)
    }
    return this != null &&
        userId.isNotBlank() &&
        !email.isNullOrBlank() &&
        !phoneNumber.isNullOrBlank()
}

suspend operator fun invoke(): UserData {
        val userData = getUserData()
        val contact = getUserContact()
        return when {
            contact.isValid() -> userData.fillInWithUserContact(contact)
            else -> userData
        }
    }

compiler is complaining

contact

inside

invoke

fillWithUserContact

is nullable. shouldn’t

contract

ensure it’s not treated as nullable?

Ayfri

03/11/2022, 4:34 AM

Is there a more efficient way than

round(number / length) * length

to round a number by a length ?

No_One

03/11/2022, 10:40 AM

Hi All, I am new to Kotlin (have a lot of java exp), what is the best way to get started to master kotlin ? I am okay to buy courses etc as I need to be up and running soon as my new project demands it. will be using it for building microservices with spring and Kafka etc.

oday

03/11/2022, 2:00 PM

how can i get back these variables to use them?

"ticket-alert/remove/(?<id>.+)/(?<hash>.+)".toRegex()

Nat Strangerweather

03/11/2022, 6:27 PM

Hi, hope this is the right place. I am trying to loop through a list of Strings so that I can create an array called Letter which is made of a String and an Int. The problem is that whatever I do, I only ever get the last value of my list of Strings. What could I be doing wrong?

fun savedData(): Array<Letter> {
        val arr = mutableStateOf(boardLetters)
        if (savedValues != null) {
            for (item in savedLetters!!) {
                arr.value = Array(28) {
                    Letter(item, 0)
                }
            }
        }
        return arr.value
    }

For info: boardLetters is this:

boardLetters: Array<Letter>

Thanks for any help.

Andy Jiang

03/11/2022, 11:51 PM

Hi, I'm new to Kotlin and I have a question about the code snippet from the official doc:

val a: Int = 100

val boxedA: Int? = a

val anotherBoxedA: Int? = a

val b: Int = 10000

val boxedB: Int? = b

val anotherBoxedB: Int? = b

println(boxedA === anotherBoxedA) // true

println(boxedB === anotherBoxedB) // false

Andy Jiang

03/11/2022, 11:53 PM

val a: Int = 100
    val boxedA: Int? = a
    val anotherBoxedA: Int? = a
    
    val b: Int = 10000
    val boxedB: Int? = b
    val anotherBoxedB: Int? = b
    
    println(boxedA === anotherBoxedA) // true
    println(boxedB === anotherBoxedB) // false

:thread-please: 3

jcechace

03/12/2022, 6:24 PM

I have a library written in Kotlin which is then used as a dependency from Java code. Is it expected that KClass#primaryConstructor returns null?

Title

jcechace

03/12/2022, 6:24 PM

I have a library written in Kotlin which is then used as a dependency from Java code. Is it expected that KClass#primaryConstructor returns null?

clazz.primaryConstructor!!.call(param)

When this line is executed from Kotlin code the primary consructor is returned. In Java I get a null value.

wrongwrong

03/12/2022, 7:03 PM

I don't know if I understand your question, but for example, the following will cause the

primaryConstructor

to be

null

even in a

Kotlin

class.

import kotlin.reflect.full.primaryConstructor

class C {
    val v: Int

    constructor(v: Short) { this.v = v.toInt() }
}

fun main() {
    println(C::class.primaryConstructor) // -> null
}

The

primaryConstructor

will never be

null

for a

data class

jcechace

03/13/2022, 3:48 PM

@wrongwrong I get that. In my case the class has primary constructor (its mandated by supertype). My issues is that with the ``primaryConstructor`` is when it’s accessed as part of Kotlin code base it’s there, when it’s from java it’s not… thinking about it… it makes perfect sense since Java classes probably don’t have a primary constructor :)… Thanks for being my rubber duck

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