Is there any kotlin-first json path library out there?

Seeking for advice here. My workflow is as below: Mobile app send photo/video to spring boot backend, spring boot upload it to cloud object storage and add metadata to database. Question is: While spring boot is uploading file to cloud, how to respond mobile client immediately and notify them about upload success? I thought of creating work request and let client poll it.

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Is it possible to make @Nullable annotations in libraries currently not understood by the kotlin nullabillity annotation magic count as nullable values somehow? For context, im using a library that defines its own @nullable, and id like kotlin to consider that annotation such that my calls to annotated functions from that library are properly detected as returning nullable values. Ive looked at the JSR305 compiler flag thingy, but im not sure if thats actually what i need here - at least it doesnt do anything, and im unsure how kotlin would know if the specified annotation is supposed to mean non-null or nullable

This works :

fun <T, M : MutableCollection<T>> Collection<T>.partitionTo(left: M, right: M, predicate: (T) -> Boolean): Pair<Collection<T>, Collection<T>> {
    forEach {
        if (predicate(it)) left += it else right += it
    }
    return Pair(left, right)
}

so as this:

fun <T, C : Collection<T>, M : MutableCollection<T>> C.partitionTo(left: M, right: M, predicate: (T) -> Boolean): Pair<Collection<T>, Collection<T>> {
    forEach {
        if (predicate(it)) left += it else right += it
    }
    return Pair(left, right)
}

This doesn’t compile… why?

fun <T, C : Collection<T>, M : MutableCollection<T>> C.partitionTo(left: M, right: M, predicate: (T) -> Boolean): Pair<C, C> {
    forEach {
        if (predicate(it)) left += it else right += it
    }
    return Pair(left, right)
}

when you cast it, then i works then but it’s unsafe cast..

fun <T, C : Collection<T>, M : MutableCollection<T>> C.partitionTo(left: M, right: M, predicate: (T) -> Boolean): Pair<C, C> {
    forEach {
        if (predicate(it)) left += it else right += it
    }
    return Pair(left as C, right as C)
}

Why can’t typesystem figure out that M is covariant towards C ?

The

ifEmpty

extension function on String is defined like this in the Kotlin stdlib:

public inline fun <C, R> C.ifEmpty(defaultValue: () -> R): R where C : CharSequence, C : R =
    if (isEmpty()) defaultValue() else this

However, if you try to define exactly the same function in your own code you get this error:

Type parameter cannot have any other bounds if it's bounded by another type parameter

So how is the standard library circumventing this error? I even checked and there aren't any

@Suppress

annotations in the file at all regarding this, so how in the world did they stop that error?

For a kotlin code-gen tool, any recommendation for assertion library for writing expectations on generated code? I am inclining towards some kind of approval testing framework in Kotlin, any recommended testing-library? I prefer to avoid going via verifying AST nodes route as it gets very verbose. FWIW, We are using kotlinpoet to generate code.

I am having a hard time.

Is it possible to use the

@DslMarker

annotation on a

suspend

scope receiver ? I’m getting an

java.lang.IllegalStateException: Backend Internal error: Exception during IR lowering

exception when I write the following code, but don’t face any issue when I remove the

suspend

modifier :

@DslMarker
annotation class MyDslMarker

@MyDslMarker
interface MyDsl

fun something(
    scope: suspend MyDsl.() -> Unit,
) {
}

fun main() {
    something { }
}

is there a simpler example of using

kotlinx-benchmark

with .kts Gradle scripts? example at https://github.com/Kotlin/kotlinx-benchmark/tree/master/examples is a complex one, and trying to simplify I'm getting nowhere...

What is the appropriate channel for discussing Kotlin serialization issues?

Hi All, Do we have command line or java library that can be used to decompile kotlin classes ?

Since I have no one in house to ask this of, I'm asking here. Looking for broad strokes architectural advice. My company needs a method to create tickets from emails in a multi-tenant system. Each tenant can have multiple pop/imap servers configured. What would you recommend as a high level architecture for monitoring an arbitrary number of email servers and writing to an aws aurora db cluster?

I read that you shouldn't inline large functions. Is it better to not use inline here?

inline fun <ResultType, RequestType> networkBoundResource(
    crossinline query: () -> Flow<ResultType>,
    crossinline fetch: suspend () -> RequestType,
    crossinline saveFetchResult: suspend (RequestType) -> Unit,
    crossinline onFetchSuccess: () -> Unit = { },
    crossinline onFetchFailed: (Throwable) -> Unit = { },
    crossinline shouldFetch: (ResultType) -> Boolean = { true }
) = flow {
    val data = query().first()

    val flow = if (shouldFetch(data)) {
        emit(Resource.Loading(data))

        try {
            saveFetchResult(fetch())
            onFetchSuccess()
            query().map { Resource.Success(it) }
        } catch (t: Throwable) {
            onFetchFailed(t)
            query().map { Resource.Error(t, it) }
        }
    } else {
        query().map { Resource.Success(it) }
    }
    emitAll(flow)
}

Hi all, can anybody explain why Kotlin doesn't allow smart-cast on receiver after function call in infix manner? Consider this toy example:

Can I compose annotations somehow? I have these two anntations everywhere

@Provides
@JvmStatic
fun widgetUpdater() ..

Can I turn it somehow to this? where

@ProvidesAndJvmStatic

would reference then the daggers

@Provide

and kotlins

@JvmStatic

inside?

@ProvidesAndJvmStatic
fun widgetUpdater() ..

is there a library or an stdlib function or some way to represent trees through a print statement?

I'm trying to learn coroutines and I found a strange thing. If I save a reference to CoroutineScope to a field, and then a method uses this field to launch some jobs, it seems to be unable to cancel such jobs. My example has about 40 lines, I don't want to break some mobile user's screen, so it is linked here: https://gist.github.com/StragaSevera/b294625b927eb002be8987804de31013 This code should stop counting when I press "Enter", but it does not cancel the coroutines and counts forward after the "Cancelled" message 😃 Also, the bug happens if I pass the scope as an argument to the

start()

method, but does not happen if I remove the class and copy contents of the

start()

method to the

main()

function. It seems like there is some caching issue...

Somebody has experience or a great resource how to build Kotlin Gradle project with Github Actions?

Hey - my son (14, bright) is interested in spending February half term learning Kotlin. He’s basically a complete beginner programmer. We’ve found this: https://www.udemy.com/course/kotlin-course/ Any experience with it? Or other suggestions? Grateful for any feedback or thoughts. Thanks!

Hey, I'm new here. I'm having problems trying to use Kotlin Jsr223, it just throws an NPE on the .eval function call... any ideas? Also is this the right place to ask?

Inside an extension function, how can I call another function without an implicit

this

being used? In my IntelliJ Plugin have this:

fun Project.foo {
   ...
   service<SomeApplicationService>().bar()
}

The

com.intellij.openapi.components.service.kt

file has two

service

functions:

inline fun <reified T : Any> service(): T = ApplicationManager.getApplication().getService(T::class.java)
inline fun <reified T : Any> Project.service(): T = getService(T::class.java)

Because I'm inside a

Project

extension function, it is implicitly calling

this.service<SomeApplicationService>().work()

and thus the

Project.service()

extension function rather than

service()

. I was able to workaround by creating a separate

applicationService()

convenience function. But I have to imagine this is not an unheard of situation and was wondering if there is some syntax to say not to use the implicit

this

. It's a top-level function, to I'm not aware of any

this@

syntax for this case.

I sort this list to get the smallest occurrence of a property. Is there a simpler way in Kotlin?

val sortedArticles = cachedArticles.sortedBy { article ->
    article.updatedAt
}
val oldestTimestamp = sortedArticles.firstOrNull()?.updatedAt

is there a way to write

foobar

so that I can pass ::class of either subclasses? https://pl.kotl.in/Y5NcoKR3K

Did anyone make UML diagrams of Kotlin code recently? My Intellij Ultimate doesn't show relations between classes and won't create any links. I've lost half day on trying to find a tool or plugin that would either convert kotlin code to UML or edit IntelliJ's '.uml' file.

Hi all Does anyone know why

StateFlow

doesn't emit new changes of a

MutableList

? this is my code:

_selectedLanguages.value = _selectedLanguages.value.apply {
   if (changedLanguage.isSelected)
      add(changedLanguage)
   else
      remove(changedLanguage)
}

Why is it important that extra programming features (coroutines) are added via libraries instead of the language directly? Ive heard this "benefit" of kotlin stated a few times but never really understood whats so beneficial. I can guess one benefit: a library can evolve faster than a language.

How do i convert this java annotation to kotlin code

@Target({METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE})

@Retention(RUNTIME)

@Documented

@Constraint(validatedBy = CustomerTypeSubSetValidator.class)

public @interface CustomerTypeSubset {

CustomerType[] anyOf();

String *message*() default "must be any of {anyOf}";

Class<?>[] groups() default {};

Class<? extends Payload>[] payload() default {};

}