Hi all, I am attempting to make a generic abstract class for Plugin's whose subclasses can enforce strongly typed method parameters. I was able to get this mostly working using the following but have hit issues when trying to iterate over the concrete Plugin subclasses in a generic manner. Here is a short(ish) sample of what I am attempting. Any suggestions on how to approach this? Thank you in advance!

Can anybody tell me, if this is possible?

Hello Kotliners, I'm new to Kotlin but longtime experience with Java, C(++). My host is an Android Tablet (linux aarch64) with termux (and nearly full linux dist/terminal emulator) as dev environment and have no issue to use NDK with clang 12.0.1 for crosscompiling and latest GraalVM working perfectly. I have no Desktop/Notebook etc (Digital Nomade). Then I tried Kotlin/Native without success, because of incompatibility of my OS. Is there a workaround for my platform? What about rebuilding the kotlin/native module from source and hacking my OS into the Platform.kt? My use-case is to work with executables/libraries written in Kotlin with cinterop. Thank you in advance

Very curious to know what techniques Kotliners use for managing resources. In the example below I manage a resource via the Closable technique:

interface Closable {
  val isClosed: Boolean

  fun close()
}

class ResourceX : Closable {
  val isClosed: Boolean
    get() = _isClosed
  private var _isClosed = false

  fun close() {
    if (!_isClosed) {
      // Do cleanup here.
      _isClosed = true
    }
  }

  fun operation() {
    if (_isClosed) throw IllegalStateException("ResourceX is closed")
    // Do stuff related to the operation here.
  }
}

This compiles in Kotlin 1.5.21 but fails to typecheck in Kotlin 1.5.30-RC:

fun f(l: MutableList<String>) {}
@ExperimentalStdlibApi
val l: List<Any> = buildList {
    javaClass
    f(this)
}

Did something change with builder inference?

I want to turn an

Int?

into a

String?

but if the

Int?

is

null

I don't want to have a literal

"null"

String, I want the string value to be

null

. Is there an operator for this or do I have to check it manually?

Would be great if there was a modifier to make a variable have public getter but private setter... So, instead of this:

var a = 2

private set

we could write something like

local var a = 2

I believe it cannot handle the success, failure response from the Kotlin API.

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General question for someone with greater wisdom. This code (run with kotlin 1.5)

1:    val aut = setOf(2, 3, 1, 4, 0)
2:    print("$aut")
3:    val aux2a: List<Int> = aut.dropWhile{ 2 < it }
4:    a2.containsAll(aux2a) shouldBe true
5:    (aux2a.size < a2.size) shouldBe true

fails (i.e.

(aux2a.size < a2.size)

is

false

) at line 5. the documentation for

dropWhile

says :

Returns a list containing all elements except first elements that satisfy the given predicate.

I would have expected that at least item

3

(from line 1) xor item

4

would have been dropped. Perhaps both under certain circumstances (ordering is not a property of

Set

). What is the expected behavior of

dropWhile

for a Set?

hello guys

Should this channel be read only for almost everyone and be used for announcements or something so?

out of curiosity: is there a nice way to abbreviate

fun foo(): Boolean {
  val bool = isConditionMet()
  if (bool) {
     log(…)
  }
   return bool
}

“Cascade if can be replaced with when” warning but sometimes it’s a false positive, for example if I have an

if

condition (at least 3 branches) where the checks are things like

Build.VERSION.SDK_INT > 12

and then branch depends on such a later SDK level. How to suppress this warning?

Where can I learn more about kotlin compiler? Under the hood architecture and all.

Hello All! Im looking for way to create app using ktor and kotlin/js. The catch is that i want to create web app based on windows(drag and drop items that can be minimalize or close) and im totally confused with a way to use routing there. Did someone can help me understand that concept?

Is there an existing cached computed property pattern in Kotlin? For example:

var firstName: String = "Charlie"
var lastName: String = "Brown"
val fullName: String by lazy {
  "$firstName $lastName"
}
println(fullName) // Charlie Brown

firstName = "Snoopy"
// Let "fullName" know it will need to recompute the next time it is accessed
println(fullName) // Snoopy Brown

I’m currently going down writing my own

ReadWriteProperty

for it but wondering if there is an existing pattern for this already? Thanks!

Why does this break smart cast 🤔

val showSelectNewTaskConfirmationDialog = newTask != null
if (showSelectNewTaskConfirmationDialog) {
    // smart cast for newTask here not working
    [...]
}

I'm trying to make extensions that wraps part of the behavior of interfaces without changing the interface signature. Not finding a scalable solution though. Anyone finding a decent solution would be awesome 🤗 Problem:

interface Counter {
    fun add()
    fun remove()
}

// We have some interfaces extending counter
interface MyCounter : Counter {
    fun doStuff()
}

interface MyOtherCounter : Counter {
    fun doOtherStuff()
}

// Implements counter by wrapping a counter and calling add/remove twice.
class DoubleCounter(val baseCounter: Counter) : Counter {
    override fun add() {
        baseCounter.add()
        baseCounter.add()
    }
    override fun remove() {
        baseCounter.remove()
        baseCounter.remove()
    }
}

// These two are okay, but very boilerplate and non-scalable
fun MyCounter.double(): MyCounter {
    val double = DoubleCounter(this)
    return object : MyCounter by this {
        override fun add() = double.add()
        override fun remove() = double.remove()
    }
}
fun MyOtherCounter.double(): MyOtherCounter {
    val double = DoubleCounter(this)
    return object : MyOtherCounter by this {
        override fun add() = double.add()
        override fun remove() = double.remove()
    }
}

// This is illegal, is there any way to do this or similar?
inline fun <reified T: Counter> T.double(): T {
    val double = DoubleCounter(this)
    return object : T by T {
        override fun add() = double.add()
        override fun remove() = double.remove()
    }
}

when (result) {
    Result.Loading -> {}
    is Result.Success -> SomeScreen(data= (dataResult as Result.Success<List<SomeData>>).value)
    is Result.Error -> {}
}

How do I prevent casting type on Success? My Result class

sealed class Result<out T> {
    object Loading : Result<Nothing>()
    data class Error(val message: String) : Result<Nothing>()
    data class Success<T>(val value: T) : Result<T>()
}

📣 Hi everyone <!here>! This is a follow-up on our change proposal for this Slack space. First of all, thank you to everyone who shared their feedback and applied to be a moderator. All of us in the community appreciate it! 🙏 Next steps: 1. We’ll rename #general to #announcement and make it read-only starting August 18 (Wednesday). #getting-started will replace #general as a channel where folks who are new to Kotlin (and this Slack space) can ask questions. Any newcomer will automatically join the #getting-started channel. 2. We’ll be archiving duplicated, private, and unauthorized shared channels starting August 18. All attendees and owners will get notifications 72 hours prior to archiving.

Hi

enum class Role(val letter: Char) {
    APPROVER('U'),
    ADMIN('D'),
    INQUIRER('R'),
    OPERATOR('O');
}

we have create this enum for code readability and we don't have direct control over how server is returning constants for the user roles, so they have done it this way 'U' , R etc apiRespose.role = "U" Role.valueOf(apiResponse.role) will not work ,as it is expecting 'APPROVER' as input . How can i achieve same benefit of Role.valueOf( ) wrt ot the 'letter' attribute in the enum

Good day, I'm using reflection method to handle the last call method example

fun foo(name: String) {
  lastCallMethod = ::foo
}

Now I want to call the method

lastCallMethod

May I ask if there is a way to retrieve the

name

String that pass using reflection?

Hi, how do we pass the string parameter 'emessage' to the exception instance

fun String?.throwOnEmptyOrNull(emessage: String, exceptionClass: Class<out Exception>): String {
    return this.takeIf { !it.isNullOrBlank() } ?: throw exceptionClass.newInstance()
}

val ss : String? = null
println("test 1 ${ss.throwOnEmptyOrNull("roles can't be empty or not", IllegalArgumentException::class.java)}")

This is working for me, however i'm stuck at passing the message to exception

Just me or does the left side on the docs not show anything? https://kotlinlang.org/docs/home.html

With kotlin 1.5.21 installed on my path, in my shell when I run

kotlin

and then at the REPL prompt I type

(-1).toUInt()

or

1u - 2u

, then the result is

kotlin.UInt = -1

. Is that expected?

kotlin.UInt

ranges from 0 to 2^32-1, but can it be rendered as negative too somehow? Or is

kotlin.UInt = -1

actually equal to

2^32-1

?

How to supress unused warning for the public members only?

Who moderates the community?

Is it possible with contracts to imply the return type of a method to be of type T where T is a reified type parameter, so that smartcast is possible outside the method?