I want reduce this code, merging

vidID

and

idMissing

in a single variable.

data class File22(val fileName: String, val vidID: Int = - 1)

val files22 = ..... // Intance of 'File22'

val vidID     = files22.map { it.vidID } // Array of Int e.g: [1,3,4,7]
val idMissing = vidID.filterIndexed { index, i -> !vidID.contains(index)} // Result: idMissing -> 2,5,6

Question about inheritance and parameters

import kotlinx.serialization.Serializable

@Serializable
abstract class TagsDto( val id: String?, val name: String, val icon: String?, val color: String? )

@Serializable
class LocationTagsDto( id: String? = null, name: String, icon: String?, color: String? )
    : TagsDto( id = id, name = name, icon = icon, color = color)

This fails compilation on the second

@Serializable

This class is not serializable automatically because it has primary constructor parameters that are not properties

I don’t want to have

LocationTagsDto

add any new property to

TagsDto

. How can I make this work? Thanks in advance.

Because your

on

function is not inline, that lambda is considered as a closure, and because closure is self-contained, it must "capture" stuff in the outer scope, and now that it's not possible to directly modify a local variable in a closure, that local is wrapped into an object with a var member for the closure to "modify".

Is there a way I can extract those validate blocks into a reusable function?

fun Application.configureValidator() {
    install(RequestValidation) {
        validate<ClientUserDto> {
            val validationResult = it.validate(it)
            if (validationResult is Valid)
                ValidationResult.Valid
            else
                ValidationResult.Invalid(
                    validationResult.errors.map { error ->  "${error.dataPath} ${error.message}" }
                )
        }

        validate<ClientListDto> {
            val validationResult = it.validate(it)
            if (validationResult is Valid)
                ValidationResult.Valid
            else
                ValidationResult.Invalid(
                    validationResult.errors.map { error ->  "${error.dataPath} ${error.message}" }
                )
        }

        validate<ClientListItemDto> {
            val validationResult = it.validate(it)
            if (validationResult is Valid)
                ValidationResult.Valid
            else
                ValidationResult.Invalid(
                    validationResult.errors.map { error ->  "${error.dataPath} ${error.message}" }
                )
        }
    }
}

Hey! I was wondering if it was possible to automatically cast a sealed class to one of it's children if a certain condition is met.

sealed class Response(val success: Boolean) {
    class Success : Response(true)
    class Failure : Response(false)
}

So from this I'd like to do this.

// Example
val res = Response(true)

if(res.success) {
  // cast to Response.Success
} else {
  // cast to Response.Failure
}

I know I can probably just use the

is

clause but I think it'd be a tad bit nicer to do it like this, if it's not possible I'll just use

is

. Thanks in advance!

what does

interface.()

mean? e.g.

interface.() -> Unit

I thought Kotlin keywords are soft keywords and context-specific?

data class MyDataClass(
    val package: String, // error
    val hello: String
)

Is there a way to check if a given KClass extends another KClass? I saw isSubclassOf but that doesn't exist in Kotlin/Native it seems If no good way to do that exists, is there a way to easily define structs that can automatically be converted to a ByteArray?

Can I use the UInt class to make this easier to read?

private fun getUInt16(firstByte: Byte, secondByte: Byte): Int =
    firstByte.toInt() shl 8 and 0xFF00 or (secondByte.toInt() and 0xFF)

How can I read multiple files concurrently using coroutines ? I did this but the IDE throws me a warning saying

inappropriate blocking method call

for

FileInputStream

and

read

functions.

suspend fun uploadFiles(files: List<File>, convertToPdf: Boolean): List<String> = coroutineScope {
	return@coroutineScope files.map {
		async {
			uploadFile(it, convertToPdf)
		}
	}.awaitAll()
}
	
@Throws(IOException::class, FileNotFoundException::class)
suspend fun uploadFile(file: File, convertToPdf: Boolean): String = withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
	val chunk = ByteArray(4096)
	val inputStream = FileInputStream(file)
	val res: Flow<FileChunk> = flow {
		while(true) {
			val size = inputStream.read(chunk)
			if(size <= 0) break
			val fileChunk = FileChunk.newBuilder().setConvertToPdf(convertToPdf)
				.setChunk(ByteString.copyFrom(chunk, 0, size)).build()
			emit(fileChunk)
		}
	}
	val response = blockingStub.uploadFiles(res)
	return@withContext "Some String"
}

Recognizing this is generally a bad idea… is there any way to force the compiler to allow me to pass a null value into a Java method with a parameter annotated as

@Nonnull

?

Hey! I was wondering if it was possible to possibly use contracts to cast data as not null as long as the type does not equal Unit. I use

Unit

to represent when an action has been preformed but no data is returned, so if it's anything but unit then there's data in the class.

sealed class Test<out T>(val success: Boolean) {
  abstract val data: T?

  class A<out T>(override val data: T?) : Test(true)
  class B<out T>(override val data: T?) : Test(false)
}

fun Test<Any>.isSuccess(): Boolean {
  contract {
    returns(true) implies(this@isSuccess is Test.A)
    // if T != Unit then data != null
  }
  return this is Test.A
}

What is the proper way to use Flow to run tasks for a given amount of time while also utilizing rate limiting? I have the following:

runBlocking {
    withTimeoutOrNull(1000) {
        inputs.asSequence().repeat().asFlow()
            .rateLimiter(rateLimiter)
            .map { executeInput(it) }
            .toList()
    }
}

val rateLimiter = RateLimiter.of(
    properties.name,
    RateLimiterConfig
        .custom()
        .limitForPeriod(properties.rateLimiter.limitForPeriod)
        .limitRefreshPeriod(properties.rateLimiter.limitRefreshPeriod)
        .timeoutDuration(properties.rateLimiter.timeoutDuration)
        .build()
)

/**
 * @see <a href="<https://stackoverflow.com/questions/48007311/how-do-i-infinitely-repeat-a-sequence-in-kotlin>">Infinite Sequence</a>
 */
private fun <T> Sequence<T>.repeat() = sequence { while (true) yieldAll(this@repeat) }

Here I’m attempting to turn a list of inputs into an infinite sequence that I can then throttle with a RateLimiter + time out after a certain duration, but neither seem to be working.

can anybody tell me ‘scanner.nextInt( )’ equivalent in kotlin without using scanner class

👋 Hello, team!

I want to pass a parameter to a function (actually a super class constructor call), and this parameter is a complicated expression and I tried using

run { ... }

. However,

run

is overloaded as both an extension and non-extension function. Since the context includes an implicit "this" receiver, Kotlin favours calling the extension version. How can I force it to run the non-extension version?

I have a question please, I'm trying to fix the highlighted line, but I don´t achieve to fix it. The suggestion from IntelliJ is to put

root.<String>get("codes")

but it always shows me another failure, does someone know about JPA Specification that you can help me?

👋 Hello, team! What would be the recommended approach to set up the KMM project and repo? Is it better to have iOS and Android apps in the same repo along with the shared module or is it better to separate them out? wanted to check the experience so far from the community with different approaches. Curious to hear some great use-cases!

hey hi need some help on setting kotlin exposed framework transaction isolation level to 2 (read committed ) from level 4 globally..

what can I use to serialize a data class to compilable kotlin code? Just toString() and some manual editing? Is there something nice?

can I not have a map of String, Array<String> ?

val technologies = mapOf<String, Array<String>>("Jetpack Compose", arrayOf("Compose"))

for (j in 0 until pdfReader.numberOfPages) {
                extractedText += PdfTextExtractor.getTextFromPage(pdfReader, j + 1)

                technologies.forEach { (key, values) ->
                    values.map {
                        if (extractedText.contains(it, ignoreCase = true)
                            || extractedText.contains("${it}s", ignoreCase = true)
                        ) {
                            occurrences[key] = occurrences.getOrDefault(key, 0) + 1
                        }
                    }
                }
            }

            println(occurrences)
            val person = extractedText.split(" ")[0].trim { it == ',' }
            results[person] = occurrences

I would like to clear

occurrences

after I’m done with it so that I can load it again with new values after I insert it into

results[person]

but doing that is causing it to store an empty map into `results[person]`…

In Book.kt:

data class Book(val isbn: ISBN, val title: Title)
@JvmInline value class ISBN(val value: String)
@JvmInline value class Title(val value: String)

Somewhere in BookDAO.java:
new Book("123","Thundercats");

When I'm looking at the code in IntelliJ, it's simply compiling (no red squiggly lines). When I run a

mvn clean install

it also just compiles. But when I do a build (ctrl+F9), I'm getting this:

java: Book(java.lang.String,java.lang.String) has private access in Book

When I define book as

data class Book(val isbn: String, val title: String)

compilation does succeed. What is going on? It smells like intelliJ is using an older Kotlin version to compile or something? In the build output I'm getting this:

...
Kotlin: kotlinc-jvm 1.7.20 (JRE 17.0.2+8)
...
javac 11.0.9 was used to compile java sources

I'd like to try to get kotlinc-jvm to use JRE 11 to compile, but don't know how.

Is there a cleaner way to do this ?

var firstChunk = true
val fileChunks = flow {
	if(firstChunk) {
		val metadata = MetaData.newBuilder()
			.setPath(file.path)
			.setConvertToPdf(BoolValue.of(convertToPdf))
			.build()
		emit(FileUploadRequest.newBuilder().setMetadata(metadata).build())
		firstChunk = false
	} else {
		while(true) {
			val size = inputStream.read(chunk)
			if(size <= 0) break
			val fileChunk = FileChunk.newBuilder()
				.setData(ByteString.copyFrom(chunk, 0, size)).build()
			emit(FileUploadRequest.newBuilder().setContent(fileChunk).build())
		}
	}
}

Trying to create a flow of file bytes where the first byte is metadata of the file.

Hello guys. I am JS developer new in Kotlin world. Want to flatten list to single list. In JS i use simple recursive function that is seems does not work correctly. In thread is mock data how list looks like.

Hello guys, i need to know why i need to create custom annotation in Kotlin? what is the benefit of creating custom annotation? Thank You

I am a Swift developer learning Kotlin since last 2 days by following https://play.kotlinlang.org. I have doubt related to lambdas. Question - In Swift, we have a similar concept like lambda called as closure. But, they are distinctly differentiated when passing them into function arguments by marking them as

@escaping

or

@non-escaping

which denotes if they will be executed asynchronously or synchronously respectively. How do we differentiate between asynchronous or synchronous lambdas in Kotlin?

Hey guys I'm trying to convert an odd lambda expression from a gradle plugin to Kotlin:

project.getExtensions().configure(PublishingExtension.class, extension -> {
            extension.getPublications().registerFactory(MavenPublication.class, new MavenPublicationFactory(
                    dependencyMetaDataProvider,
                    instantiatorFactory.decorateLenient(),
                    fileResolver,
                    project.getPluginManager(),
                    project.getExtensions()));
            realizePublishingTasksLater(project, extension);
        });

However I'm having issues with the syntax for this in Kotlin.

val values = match.groupValues.drop(1) // ["kotlin slack"]
var newResponse = filter.response!! // "hi $1"
values.forEachIndexed { index, value ->
    newResponse = filter.response!!.replace("\$$index", value)
}

// newResponse = "hi kotlin slack"

Is there some cleaner way of doing this? I wanna replace

$0

,

$1

,

$2

, etc, with its corresponding value