I'm trying to cram out some static dispatch from a reified type, but no luck so far:

fun foo(dummy: Int?) {}
fun foo(dummy: String?) {}

// This causes a compilation error.
// You get 
//   reified.kt: (8, 5): None of the following functions can be called with the arguments supplied: 
//   public fun foo(dummy: Int?): Unit defined in root package in file reified.kt
//   public fun foo(dummy: String?): Unit defined in root package in file reified.kt
inline fun <reified T> bar() {
    // As the function is inlined and the type parameter reified, I'm hoping for static dispatch,
    // i.e. depending on T, one of the overloads for foo() should be chosen.
    foo(null as? T)
}

// This function has no problems compiling, static dispatch works as expected.
fun baz() {
    foo(null as Int?)
    foo(null as String?)
}

Why do I get a compilation error from

bar

calling

foo

? I guess it has something to do with Kotlin instantiating the

bar

function even though it's supposed to be inlined yet never called (with an actual type parameter), but I haven't found the reason yet (I read https://kotlinlang.org/spec/runtime-type-information.html#runtime-available-types but found no explanation).

Hi guys, is there any way to get a slice of a ByteArray without copying the content in a new ByteArray? Say I have a ByteArray of 100 bytes and I just want a slice (without copying the original ByteArray) from 2 to 10 for example

fun getDomain(obj: Any) {
  when(obj) {
    is KrsProject -> obj.someMemberFunctionOnKrsProject()
  }
}

Why would this work? Doesn’t the type get erased?

What can I do if debugging is painfully slow? Stepping takes ages and loading data too 😕

Dear gradle plugin authors. While working on my npm-publish plugin I've discovered how painful it is to write gradle files for functional tests efficiently. So I've written a single-file DSL for you to drop-in to you projects that puts at least some formatting/validation on gradle buildscript generation. It could be used for any kotlin file generation as well. Here's a snippet and I'm looking forward to hearing your thoughts!

It would nice to have Kotlinx serialization to support XML from Okio.

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Can someone explain why this works?

fun listOfArrays(): List<Array<Any>> {
  return listOf(arrayOf("1", 0))
}

But not this?

fun listOfArrays(): List<Array<Any>> {
  // Type mismatch: inferred type is List<Array<out {Comparable<*> & java.io.Serializable}>> but List<Array<Any>> was expected
  return listOf(arrayOf("1", 0)).map { it }
}

Is there a trick to get use

T?

in a place where you need

T

? Unfortunately there’s no

T!

😄 Alternatively in a function where I want a non-nullable

T

for

reified T: Any?

. Basically

T & Any

.

Hey guys, we have created a linter (checker + autofixer) for Kotlin with a huge number of rules. Will be great if you will support it at least with a very simple thing: star on a GitHub: https://github.com/cqfn/diKTat But if you will have a chance try it in your CI/CD :)

What time zone is the 1.4 event happening?

How did they come up with the name Kotlin by the way?

Is there any overview which version of kotlin supports which java version? I just know by trial and error that 1.4 now supports Java 14, but would love some overview if that exists?

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I've noticed a while ago that in some cases I can't see the source code (only some generated/decompiled) code when I try to look at Koltin classes. For example the source of

Channel

looks like this when I Ctrl + Click on it:

public interface Channel<E> : kotlinx.coroutines.channels.SendChannel<E>, kotlinx.coroutines.channels.ReceiveChannel<E> {
    public companion object Factory {
        public const final val BUFFERED: <http://kotlin.Int|kotlin.Int> /* compiled code */

        internal final val CHANNEL_DEFAULT_CAPACITY: <http://kotlin.Int|kotlin.Int> /* compiled code */

        public const final val CONFLATED: <http://kotlin.Int|kotlin.Int> /* compiled code */

        public const final val DEFAULT_BUFFER_PROPERTY_NAME: kotlin.String /* compiled code */

        internal const final val OPTIONAL_CHANNEL: <http://kotlin.Int|kotlin.Int> /* compiled code */

        public const final val RENDEZVOUS: <http://kotlin.Int|kotlin.Int> /* compiled code */

        public const final val UNLIMITED: <http://kotlin.Int|kotlin.Int> /* compiled code */
    }
}

What can I do to fix this and see the source (IDEA says that this file is called

Channel.kotlin_metadata

)?

i just noticed that Array.kt in kotlin 1.4.10 has an inline constructor but when I try to do it intellij says "Modifier is not applicable for constructor" why is this?

what am I missing?

I'm getting an error when trying to override a function that's implemented by delegation (context in thread)

Is it possible from a variable containing a class to list the possible value if the class extends enum

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Hello, what is the difference between

private val _state = MutableStateFlow<Foo>(Foo())
val state = StateFlow<Foo> get() = _state

and

private val _state = MutableStateFlow<Foo>(Foo())
val state = StateFlow<Foo> = _state

? Jetbrains and Google use the first form in their documentation, but isn't a

val

read-only regardless of whether it is specified as only having a getter or not?

The android room with a view codelab (https://codelabs.developers.google.com/codelabs/android-room-with-a-view-kotlin/#7) gives you this code to copy-paste, but doesn't explain why they use the kotlin coroutines internal function

synchronize

, or how to understand how it works. Can anyone help me figure out what this actually does? (I figured out it was an internal fn from the warning I got from Android Studio)

// Annotates class to be a Room Database with a table (entity) of the Word class
@Database(entities = arrayOf(Word::class), version = 1, exportSchema = false)
public abstract class WordRoomDatabase : RoomDatabase() {

   abstract fun wordDao(): WordDao

   companion object {
        // Singleton prevents multiple instances of database opening at the
        // same time. 
        @Volatile
        private var INSTANCE: WordRoomDatabase? = null

        fun getDatabase(context: Context): WordRoomDatabase {
            val tempInstance = INSTANCE
            if (tempInstance != null) {
                return tempInstance
            }
            synchronized(this) {
                val instance = Room.databaseBuilder(
                        context.applicationContext,
                        WordRoomDatabase::class.java, 
                        "word_database"
                    ).build()
                INSTANCE = instance
                return instance
            }
        }
   }
}

Is all this necessary? How does this differ from the more normal way I've seen people write something to cache a return value, which doesn't use

@Volatile

or

synchronized

? Something like

private var _cache: WordRoomDatabase? = null

fun getDatabase(context: Context): WordRoomDatabase {
    val cached = _cache // also, why is this necessary actually?
    if (cached != null) {
        return cached
    } else {
        _cache = Room.databaseBuilder(
                        context.applicationContext,
                        WordRoomDatabase::class.java, 
                        "word_database"
                    ).build()
        return cache
    }
}

HELP I keep getting a reference error trying to call the data class

copy

I’m a bit confused that this compiles:

val x: Int? = null
val xs: Set<Int> = setOf(1, 2, 3)
xs.contains(x) // compiles, but why?

because the type of

contains

is

public operator fun <@kotlin.internal.OnlyInputTypes T> Iterable<T>.contains(element: T): Boolean

. Does

@kotlin.internal.OnlyInputTypes

mean that `T`is defined by the type of

element

not of the receiver? I guess that would type check, as

Int

is a subtype of

Int?

- right?

A bit of a random q, does junit have something similar to https://jest-bot.github.io/jest/docs/expect.html#expectassertionsnumber it's mainly used for async code to verify that assertions are being, well, asserted

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Do you know a good assertions library for Kotlin Multiplatform? I've been using AssertJ (https://joel-costigliola.github.io/assertj/) until now, but it only works on the JVM.

Will

onItemClick

actually get inlined? I inlined it with the intention to improve performance, but I haven't seen

inline

used in a constructor before.

class MyAdapter(private inline val onItemClick: (Item) -> Unit) {
   //...
}

Hi devs, a question not related to kotlin: In git, for big feature branches, what prefix do you use for the branch?