kotlinlang #getting-started

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getting-started

Tolriq

06/03/2022, 2:53 PM

Is there a way to access a parent of a parent field via kotlin reflection without relying on kotlin reflect?

javaClass.superclass.

works for the 1st level parent but

javaClass.superclass.javaClass.superclass.

Does not for the second one 😞

Jonathan Ellis

06/03/2022, 3:14 PM

operator fun Body.iterator(): Iterator<Body> {
    val body = this
    return object : Iterator<Body> {
        var current: Body? = body

        override fun hasNext(): Boolean {
            return current != null
        }

        override fun next(): Body {
            val result = current!!
            current = result.getNext()
            return result
        }
    }
}

Jonathan Ellis

06/03/2022, 3:15 PM

I tried

var current: Body? = this@Body

but the compiler doesn't like that

:thread-please: 2

Nat Strangerweather

06/03/2022, 5:24 PM

I'm trying to to get 28 letters from an array of 90. The array of 90 needs to be shuffled so that the set of 28 letters is virtually never the same. So this is the code I use:

private fun shakeLetterBag(slice: IntRange): Array<Letter> {
        repository.arr.shuffle()
        return repository.arr.sliceArray(slice)
    }

    var boardLetters = MutableLiveData(repository.arr)

    fun loadTiles(): Array<Letter>? {
        boardLetters.value = shakeLetterBag(0..27)
        return boardLetters.value}

I am wondering if there is something wrong with my logic because I seem to be getting the occasional identical set, which statistically should not be the case. Any ideas? 🤔

Jonathan Ellis

06/03/2022, 5:28 PM

When is .forEach {} preferred, vs java-style for loop? It looks like both get support from the language, e.g. destructuring for loop values

Jan

06/05/2022, 12:34 PM

Is it right that this prints "1"?:

val tags = "".split(" ")
println(tags.size) //prints 1

:yes: 12

Lawrence

06/06/2022, 7:43 PM

is it possible to ignore new lines in a multiline string? In Java, one can use

to do so. Wondering if Kotlin has something similar

String a = "This is a long string";
String b = """
     This is a \
     long string""";
a.equals(b) // true

elect

06/07/2022, 11:14 AM

isn't possible to specify type variable on function references, is it?

Iwan Aucamp

06/07/2022, 11:46 AM

should I use ktfmt or ktlint?

Wojciech Rozwadowski

06/07/2022, 1:43 PM

How to create extension function for class implements

invoke

operator? I tried to do this with below function:

operator fun <Param, T : Any> ((Param) -> T).invoke(
    param: Param,
    onResult: (Result<T>) -> Unit
) {
    val state = runCatching { this@invoke(param) }
    onResult(state)
}

Above works fine for this function reference:

fun test(param: Int): String = "testFunction"

and lambda itself but not for this class:

class ClassTest {
    operator fun invoke(param: Int): String = "testClass"
}

Any suggestions?

fun main() {
    val testLambda = { param: Int -> "testLambda" }
    val testFunctionReference = ::test
    val testClass = ClassTest()

    testLambda(1) // returns String
    testLambda(1) { onResult: Result<String> ->
        // do sth
    }

    testFunctionReference(1) // returns String
    testFunctionReference(1) { onResult: Result<String> ->
        // do sth
    }

    testClass(1) // returns String
    testClass(1) { onResult: Result<String> ->
        // Too many arguments for public final operator fun invoke(param: Int): String defined in ClassTest
    }
}

Jonathan Ellis

06/07/2022, 2:48 PM

Is there a way to ask youtrack to show me issues that I voted for?

:not-kotlin: 1

Scott Peterson

06/07/2022, 3:47 PM

Let me know if there’s a better channel to post this in: I’ve got a

UInt8

encoded byte array that I need to convert to a UTF-8 string, using Kotlin. various things I’ve tried have converted it into the ASCII value “d”, which is the correct value. But I want the UTF-8 string value “100"

Jonathan Ellis

06/07/2022, 7:49 PM

are any of the hard-copy kotlin books worth buying and reasonably up-to-date?

👀 1

Jonathon Cain

06/07/2022, 8:32 PM

Hey ya'll, I was wondering if there might be a list of feature requests for Kotlin out there. Especially if that list has some data tied to it like the amount of user demand, where the feature might eventually live and be maintained, if anyone is actively working on it, etc... I'm aware of the Jetbrains Youtrack, but I haven't used it before. If my answer is there and I just need to learn how to look, I'm happy to learn. My goal is to get a bit more more experience with various aspects of Kotlin so I can get creative when I need to on a future KMM project I intend to start in a few months. This just seemed like a good way to immerse myself to that end. Anyway, thanks for the guidance upfront, and I hope my question didn't come off as daft.

Dragos Rachieru

06/08/2022, 9:08 AM

Hello, is there a method to calculate a value between a range? Like if I want to get a value that is

min

max

, like:

X=50

min=0

max=40

, then the result is

I need this to calculate some positions, don't know if there's a method using

IntRange

allan.conda

06/08/2022, 10:13 AM

Wrapping with

let

hides the uninitialized variable being null. Is there an explanation regarding this? Seems Kotlin (1.6.21) is not null-safe in this situation.

class SomeClass { // extremely minified code

  val foo = let { bar } // compile error (almost broke production but my unit test captured it)
  // val foo = bar // compile error (safe!)
    
  val bar = true
}

kevin_abrioux

06/08/2022, 11:25 AM

Hi, how can I invite someone on this slack?

👀 1

Jonathan Ellis

06/08/2022, 7:54 PM

is it impossible to use -- and ++ operators with a nullable Int ?

james

06/09/2022, 1:09 AM

for those who are using Kotlin in large, multi-module production codebases, what tooling are you using for Kotlin specific code coverage? we have historically used JaCoCo which served us well for many years, but our codebase is now >50% Kotlin and we’ve found that JaCoCo’s update cycle moves a little too slow for the frequency with which we update to the latest stable versions of Kotlin.. so when we bump our Kotlin version we end up seeing dramatic coverage drops when the newer Kotlin compiler adds extra branches etc to bytecode for existing code, since JaCoCo doesn’t know how to handle/filter these branches yet I’ve heard conflicting reports of how well JetBrains’ own kotlinx.kover library works (fair enough, since it is a relatively new tool) so I am exploring that, but I would love to hear what others are using for Kotlin coverage

thanksforallthefish

06/09/2022, 5:44 AM

very dumb question, why does idea complain about unsafe cast in

fun cast(value: Any?) = (value as? Map<String, String?>)

? maybe followup question, am I misusing

as?

? context, in this scenario I know that

value

might not be a map, so using

as?

on purpose since it returns

null

, but this “null-trick” makes the cast safe in my eyes, since `null`s need to be handled explicitly

Jonathan Ellis

06/09/2022, 8:31 PM

Does idiomatic Kotlin use classes to organize code or is that a relic of my Java background? Specifically, is it good form to group related stateless functions in a class's companion object, or is it better to use a sub-package?

Mark

06/10/2022, 5:10 AM

Why does this extension function not call

SpannableStringBuilder.inSpans()

fun <A : Appendable> A.inSpans(vararg spans: Any, builderAction: A.() -> Unit): A =
    if (this is SpannableStringBuilder) {
       // PROBLEM: doesn't call SpannableStringBuilder.inSpans()
       inSpans(spans = spans, builderAction = builderAction) 
    } else {
        builderAction()
        this
    }

zain

06/10/2022, 12:21 PM

How to convert Hexcode to String with Emoji? Input HexCode o/p D83EDD2A0024D83DDC3900700072006F0061007300610073006C006D006B0073006B0033002326BDFE0F

gabin

06/10/2022, 3:34 PM

Can I inherit data class?

Lawrence

06/10/2022, 6:35 PM

I have got two APIs A and B such that only one maybe active at a time but not both. I wanted to determine which type I am connected to by making two parallel calls to their respective APIs and select the first successful one. I tried using select expression with a timeout of 15 seconds. Is this a good way to achieve such a thing?

// The api I am working with is blocking and throws an error if not connected 
        suspend fun determineType(): Type?  {
            var type: Type? = null
            withTimeoutOrNull(15.seconds) {
                while (type == null) {
                    select<Unit> {
                        async {
                            runInterruptible(<http://Dispatchers.IO|Dispatchers.IO>) {
                                kotlin.runCatching { apiA.typeA }.getOrNull()
                            }
                        }.onAwait {
                            if (it != null) {
                                make = it
                            }
                        }
                        async {
                            runInterruptible(<http://Dispatchers.IO|Dispatchers.IO>) {
                                kotlin.runCatching { apiB.typeB }.getOrNull()
                            }
                        }.onAwait {
                            if (it != null) {
                                type = it
                            }
                        }
                    }
                }
            }
            return type
        }

wck

06/11/2022, 1:54 AM

Hi guys, has something changed in 1.6.21 regarding nullables? code posted in thread.

smit01

06/11/2022, 8:58 AM

Can someone give a simple code example of builder inference in new kotlin 1.7.0 version. I tried to go through docs but didn't quite understand please.😅

Nat Strangerweather

06/11/2022, 7:13 PM

Hi, I have a list of Booleans, and I need to know the index of all the ones that are false, so a list of indexes. What is the best way to achieve this?

Elizeu Silva dos Santos

06/12/2022, 6:34 PM

do we have any alternative to flyway written in Kotlin?

elect

06/13/2022, 7:49 AM

I have a two-level hierarchy with a root and one or more children. Each of these children have a list of elements they need to track, and I'd like also to have somehow a "root" list in the root that incorporates all the children lists. Is there a (easy/stdlib) way to have just the root list and then each child simply manages a subset/view of this list (removing/adding)? Ps: no synch problems, everything is serial

Title

elect

06/13/2022, 7:49 AM

something in the direction of `subList`(here) but I guess if the root or the first child modifies the list, then I have to update indices for all the other children..

ephemient

06/13/2022, 7:52 AM

if the children are immutable, sure. if they are mutable you will have to define your requirements more specifically

val child = object : AbstractCollection() {
    override val size get() = root.count { isChild }
    override fun iterator() = root.filter { isChild }.iterator()
}

elect

06/13/2022, 7:59 AM

each child has a consequential view on the (root) list, ie the first [0-10], the secon [11-40], etc

Michael de Kaste

06/13/2022, 10:16 AM

I had the same issue when I had some sealed class which was viewed by the root and the implementations managed by its children. depending on your usage combination: • root view, child view • root view, child mutate • root mutate, child mutate • root mutate, child view there are different solutions. if you have root view and child mutate, you can simply have root be a value that on every request returns a new list based on the children. You can make it better by defining your own concatenation iterator

elect

06/13/2022, 10:18 AM

i have the worst I guess, root mutate, child mutate

Michael de Kaste

06/13/2022, 10:27 AM

what needs to happen when root adds? Just add it to the final sublist?

elect

06/13/2022, 12:04 PM

yep

atm I'm leaning toward a

map<name, ArrayList>

on the root containing the corresponding children lists and then forwarding the methods I need

ephemient

06/13/2022, 12:08 PM

if the root exposes a MutableList, you'll have to figure out what to do with insertions and removals at any index and before or after any listiterator

if it's a MutableCollection, then you "only" have to figure out what to with removals before any mutableiterator and additions to the whole collection

nkiesel

06/13/2022, 7:01 PM

do I understand correctly that each child is defined as an index range of the root list? Thus, a list of items and a list (or map if children are not identified by index) of IntRange would do the trick?

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