yield

is a suspend function, so it can only be called within a suspend function or other coroutine context.

inner

is not marked as suspend, so it can’t call suspend functions.

Why kotlin default modifier is public?

Hello,

I'm learning Android development, trying to do code a simple app. Want to load a JSON file on the assets folder into a string in ViewModel (livedata). Can someone point correct way to load the JSON data (user, id:Int + name:String), shall i use GSON (looks its "old), Moshi (newer) or something else?

How do you format your Kotlin code? Do you use the IDE format action before committing, or do you rely on a Git hook to run an external tool, such as ktlint or ktmft ? I'm also a TypeScript developer and I'm very satisfied with

prettier

, which IMHO formats code in a cleaner way than those 2 Kotlin tools. ktlint looks promising, but I don't like that it also lint-checks code ; I'd expect it to focus on formatting. Any Kotlin alternative?

Using the

application

gradle plugin, how do I stop an application? The stop button is greyed out... If I close the tab, it simply keeps running in the background

I'm trying to de-dupelicate some Flow code. I basically have this method repeated pretty much identically for a bunch of different firestore queries. Is there a way to wrap this up so I don't have to do all of this cermoney for each firestore query I write?

fun getBooks(): Flow<List<Book>> {
  return callbackFlow {
    val listener =
      FirebaseFirestore.getInstance().collection("books").addSnapshotListener { value, error -> trySend(value to error) }
    awaitClose { listener.remove() }
  }
  .doSomethingWithNullValueAndError()
  .conflate()
  .map { (value, _) -> 
    value.toObjects()
  }
  .flowOn(defaultDispatcher)

Heyo! Inspired by ArrowKt’s monad comprehensions, I wanted to implement one for Kotlin’s nullable types. The problem is that I don’t really understand functional interfaces. My goal: Have a

bind

extension function on all nullable types, that is only available inside of a

nullable

block. I tried to do it like this, but the

bind

function is not reachable. What’s the proper way to do this?

class BindNullableException : IllegalAccessException()

fun interface NullableBlock<A> : () -> A {
    fun <A> A?.bind() = this ?: throw BindNullableException()
}

fun <A> nullable(block: NullableBlock<A>): A? =
    try {
        block()
    } catch (e: BindNullableException) {
        null
    }

fun main() {

    val a = getNullableA().bind() // should not work

    val nullableC = nullable {
        val a = getNullableA().bind() // should work
        val b = getNullableB().bind()
        getNullableC(a, b)
    }
}

fun getNullableA(): String? = null
fun getNullableB(): String? = null
fun getNullableC(a: String, b: String): String? = null

Inside batteryProfile flow I am collecting alertLevel flow. batteryProfile flow emit value when there is change in device battery using broadcast and alertLevel emit value when I change in seekbar in UI. What is happening in my case is that When I change the alertLevel using seek bar and currently there is no emission in the batteryProfile then it also calls lambda and the whole block of code is called again and again. But according to me it should update the level variable when there is another emission in batteryProfile.

batteryProfile(Unit).flowWithLifecycle(lifecycle).collect { result ->
   val level = alertLevel(Unit).firstOrNull()?.data ?: Constants.DEF_VAL_LEVEL
   
}

Hi, isn't there a way to create a new gradle Kotlin module in Intellij ? I just can create a Java/Groovy/JavaScript module, or HTML/Compose/Selenium/Maven and Selenium has actually a

Kotlin

module option, but else I can't find how to create a new empty Kotlin module with gradle 🤔

Hello, please i am new to Kotlin and i need to know the difference between Kotlin for android and Kotlin native (embedded and ios)

Is there an JVM in kotlin for android and in native no JVM or what?

https://youtrack.jetbrains.com/issue/IDEA-118832 not a kotlin issue

Hi all! Trying to get around my head on when to create stand alone functions vs classes with methods. It makes sense to me to make classes when there's some state that needs to be mutated. However, what about just some injected dependencies that don't change? In these cases should I just use a higher order function. Or would a class be better? Thanks!

I'm trying to find a way to model

query<Int, String>(sql: String)

so that it will output

O2<Int, String>

since it has two output types or if it's

query<Int, Int, Int>

outputting

O3<Int, Int, Int>

etc or

query<T1,T2,...,T99>(sql: String)

should return

O99<T1,T2,...,T99>

Alternatively,

query(O(Int, String)

should output

O<Int, String>

How would you go about designing such an API? I've tried a few things which I've posted on SO, I've implemented the "alternatively" part, but ran into the problem where I'm outputting

O2<Int.Companion, String.Companion>

instead of

O2<Int, String>

which I could probably solve by doing

query(O(InstanceOfInt, InstanceOfString)

, but that already looks terrible. https://stackoverflow.com/questions/73271850/make-kotlin-function-output-tnk1-kn-when-the-input-is-tnk1-companion-kn-com

is there a compiler flag or something I can set to make sure that an expression that is supposed to return

Unit

has to return

Unit

? By being able to return anything when a

Unit

is expected I have created a bug in my code where some piece of side-effecting code wasn’t “run” to return

Unit

but the compiler didn’t pick it up because you can return anything if

Unit

is expected. 😞

hello, am I right in that when using java 17 with kotlin 1.7, java sealed classes are used? reason I am asking is because of https://github.com/mockk/mockk/issues/832, so I was curious to know if there is a compiler flag to disable the usage of java sealed classes, as clearly the compiler itself can do it (when using java 11 and kotlin 1.7, java sealed classes are not used ofc)

Is there a best practice for when statements where the

else

is there to be exhaustive, but is a

no-op

? e.g.

when {
    thing is OneThing -> // do something
    thing is SomethingElse -> // do something else
    else -> { /* no-op */ }
}

It doesn't exactly fit this case from the style guide especially since the app is still under development and there could be more cases:

Prefer using

if

for binary conditions instead of

when

Is a bare

return

better? Or just sticking with

no-op

? Personal preference?

I’m surprised there’s no guidance on when to prefer

x?.let { ... }

to

if (x != null) { … }

in the coding conventions. Am I right in thinking the preference of

?.let

would be when the result is used as an expression, but

if (!= null)

is better served for control-flow?

Just starting my Kotlin journey. don't 80 days of the 100 Days of Code python course and my background is Oracle (mainly PL/SQL) and general Linux admin/WordPress. Doing the JetBrains Academy Basic Kotlin at the moment but thinking of doing https://www.udemy.com/course/android-oreo-kotlin-app-masterclass/ after that. Does this seem like a good way to go?

Question about Kotlin vs Java generics: this compiles just fine in Kotlin

open class Animal<T1, T2>

class Cat<I> : Animal<I, List<I>>()

val x: Animal<String, List<String>> = Cat()

however trying to do the same instantiation in java fails:

Animal<String, List<String>> x = new Cat<String>() // error

Is there something I can do to improve the generics in the Kotlin code so that they can be used from Java just like from Kotlin?

Regarding KotlinConf: I don't find any information at what time the event starts and ends on each day. Is it like 8am to 8pm or only afternoon?

Hi, I am doing the JetBrains beginners tutorial but it's like pulling teeth. Wondering if there are any better beginner tutorials. Something video-based with lots of exercises ideally. Something fun 🙂. I don't mind paying a bit.

I also got https://www.udemy.com/course/android-oreo-kotlin-app-masterclass/ which I am planning on doing next, or is there a better next one I should do? The multiplatform is very appealing but not sure how well it works if I wanted to make Android/iOS apps.

What are my options if I want embedded scripting language for my kotlin multiplayform game? I despise LUA from the very depths of my soul, so it would be the last option I would be looking into

I want to generate Kotlin code from another source. At the moment I have my own representation and use KotlinPoet. This works fine, but I want to improve the code, eg

!(foo == "FOO")

should refactored into this

foo != "FOO"

. Is it possible to use the Kotlin plugin/frontend and its Kotlin fixup automatically? (I know this would require mapping my internal representation to Kotlin frontend code) Or do you know some other library which has basic optimizations? Alternative I have to write these Kotlin optimization by myself

Are there any technical reasons why inside of (), line breaks can’t imply commas, similar how inside {}, line breaks imply semicolons?

Hi everyone, I am trying to figure out how to use Kotlin annotations and want to be able to annotate a function with a default error message that I can then use within the function. How do I access that error message?

@Target(AnnotationTarget.FUNCTION)
annotation class DefaultErrorMessage(val defaultErrorMessage: String)

@DefaultErrorMessage("This is a test")
fun testErrorMessage() {
  // How do I access the DefaultErrorMessage?
}

Also, would it be possible to access that message from a function called by the annotated function for example:

@Target(AnnotationTarget.FUNCTION)
annotation class DefaultErrorMessage(val defaultErrorMessage: String)

@DefaultErrorMessage("This is a test")
fun testErrorMessage() {
    testNestedAccess()
}

fun testNestedAccess() {
 // How do I access default error message?
}

how can I express,

if the values in this list are valid values in my enum

? I am doing this

if (queryParams.containsAll(GiveConsent.ConsentType.values())){

but i get this error that it expects a collection and I gave it an Array