Serialize a function to JSON Is there a way to serialize a function to JSON? I try to do Json.encodeToString(fun(i:Int): Int = i * 2) I get “Class () is not registered for polymorphic serialization in the scope of ‘Function1’. Mark the base class as ‘sealed’ or register the serializer explicitly”. Marking the class as sealed does not work in my case as I don’t want to make this class abstract. In any case, this should have nothing to do with where the code is run from. 1 post - 1 participant <a...

[Feature request] Add encrypt() and decrypt() extension functions to String Decrypting and encrypting is very complicated, but why does it need to be this way? Would it be possible to simply have an encrypt function that takes in an encryption key (that should be minimum at the size of a UUID, 128 bit), and then a decrypt function where you send in the same key to decrypt? Example: val encryptedString = "My string".encrypt(encryptionKey) println(encryptedString.decrypt(encryptionKey) The same crypto algo will be used everywhere, but is that a problem as long as the...

Missing setter implementation not detected by compiler The following compiles successfully but throws an AbstractMethodError at runtime (1.8.10). interface Interface { var a: String } open class Open { val a: String = "default" } class Impl : Open(), Interface fun main() { val x = Impl() println(x.a) x.a = "" } Why does the compiler allow this? Is this a known problem or am I missing something? 1 post - 1 participant <a...

Kotlin +KorGE Hi i started to learn Kotlin and was lokking for making turn based game.I found KorGE library but i dont know how to make turn based games in Kotlin or if KorGE will be good library for this? So can somebody can help me i dont know maby some courses how to make turn based games or some advices? 1 post - 1 participant Read full topic

Hours to upgrade Kotlin Hi, I’m new to mobile development, but have taken on responsibility for an existing app developed in 2019. I’m looking for a new dev team. One group told me that before they could work on it, I need to upgrade Kotlin, which they say requires about 35 billable hours. I need a reality check. 35 hours seems like a lot of time. I have no idea whether it’s (a) necessary or (b) if it really requires 35 hours. Does this sound reasonable? 1 post - 1 participant <a...

How do I call InputEvent.inputType in Kotlin/js I checked the standard library. Without this attribute in the InputEvent - Kotlin Programming Language, but in the standard WebAPI has this property InputEvent.inputType - Web API 接口参考 | MDN So how do I call this...

Why is awaitAll error handling so counter-intuitive? I’m noticing some counter-intuitive error-handling behavior when using awaitAll. For example: suspend fun main(): Unit = coroutineScope { val deferred = async { throw Exception("fake") } try { listOf(deferred).awaitAll() } catch (e: CancellationException) { println("CancellationException: $e") } catch (e: Throwable) { println("Throwable: $e") } } This is caught in the first catch, but if I replace listOf(deferred).awaitAll() with just deferred.await(), then the...

New test run in Kotlin/JS Has anyone successfully created a project where they have a separate JS compilation and test run using it? I’m using the IR compiler in a multiplatform project, if that makes any difference. At first it seems like the way you’re supposed to do this is use the testRuns container, with something like: kotlin { js(IR) { browser {...

Extension function with type Any I was trying to write a more generic extension function which counts elements of all lists in a map: So, instead of val Map.listElementCount: Int get() { var total = 0 for (list in this.values) { total += list.size} return total } I would like to write as I then could apply it to all Maps with a List of values val Map.listElementCount: Int get() { var total = 0 for (list in this.values) { total += list.size} return total } This...

Avoid using `runBlocking` in tests Is there a way to avoid using runBlocking in tests? I currently have the following: class ServerTest { @Test fun testLocalServer() = runBlocking { ... } @Test fun testStagedServer() = runBlocking { ... } } I would like this to somehow become: @Test fun testLocalServer() { ... } @Test fun testStagedServer() { ... } Basically, I want my code to look like the second code block but still behave exactly like the first code block. I am assuming that I will want every...

Coroutines for low latency/zero gc software I’ts been few years since i last used coroutines, nowdays i’m doing low latency and zero gc software, essentially systems where once application is bootstraped and jvm warmed up no objects are to be created especially on critical path. We often use our own event loop implementations (we = Chronicle Software) which are often busy spinning on a cpu. For some applications where interaction with an external services amounts to an event being published and another event eventually observed to read...

How to create a progress bar that shows the real completion percentage of a task I would like to add a progress bar showing the real percentage of completion of a task (compressing a video using ffmpeg) in my app. At the moment, I just found examples with delays that seem real, but they aren’t. Right now, I’m using Progress Dialog: progressDialog = ProgressDialog(requireActivity()) progressDialog.setTitle("Please wait..") progressDialog.setCancelable(false) progressDialog.setCanceledOnTouchOutside(false) but I don’t know how to show the percentage and...

Courutines cancellation exceptions Hey For Kotlin Multiplatform projects: Is it possible to implement coroutines or threads for Kotlin/Native or Kotlin Coroutines that throw a cancellation exception? Quote from this blog post where the problem of “Shrödinger’s Coroutines” is defined: Cancellation exceptions shouldn’t be ignored or suppressed, because that could cause a cancelled coroutine to...

What are my options for auto code generation from text file? I have a text file like this: name: "Foo" metric { type: COUNTER } field { name: "bar" type: BOOL } And I want Kotlin to parse the file, extract field values, and generate function, like below, and append that function to the existing file FooBar.kt fun countFoo(bar: Boolean) { println("Success: $bar") } I found code generation from annotations but are there any well supported packages in Kotlin that will allow me to do what I described or should I go back to C++ thanks...

Coroutine select - need onJoin or onAwait that cancels if not chosen If I’m not mistaken, calling onJoin on a Job inside select will NOT result in the job being canceled if another clause is chosen (same with onAwait.) However, this is absolutely functionality I will regularly use in the context of a game engine – for example, implementing a select clause like onEvent by launching a job that will invoke a suspending function under the hood (i.e. the non-select implementation) then invoking onAwait on it, ideally. However the job should be completely...

Differences between Resources and Locations plugin in ktor? The docs for them look almost identical. What is the difference? 1 post - 1 participant Read full topic

Composition visibility I suppose, internal visibility is rarely used in projects because it’s wide and packages are shuffled often. But what could be useful is a visibility scope to be seen only between children and parents or composition variables. Like class Foo() { internal_private fun invisibleOutside() {} } class Bar(foo: Foo) { init { foo.invisibleOutside() } } And it’s good to be available in interfaces as well. 1 post - 1 participant <a...

How to default null values on a data class? I have the following class with a default value for the property name. data class Location constructor( val lat: Double, val lon: Double, val name: String = "" ) Fine. If I call the constructor without passing a value for name, it initializes properly with the empty string but… Not fine, it gets called with the argument null by a deserialization framework (and maybe other frameworks). If I make the constructor parameter nullable and not a val, I can’t make it a data class so I...

Operator function for getting boolean value of object Has this ever been officially suggested? To allow something like Python’s __bool__? class BooleanThing{ operator fun bool() = true } fun main() { if (BooleanThing()) { println("Hello World") } } 1 post - 1 participant Read full topic

Trouble when interpreting Kotlin specifications Hello all, I’m having trouble figuring out how the Kotlin specification’ Syntax and grammar should be interpreted. For instance, when reading the section on while-loops, quote: 'while' {NL} '(' expression ')' {NL} (controlStructureBody | ';') Here we could see that while is followed by <a href="https://kotlinlang.org/spec/syntax-and-grammar.html#syntax-and-grammar" rel="noopener...

My experience with "select" in coroutines Hi folks, I wanted to talk a little about my experience with coroutine select in the context of a game engine. First of all, I’m very happy that it exists in Kotlin! Coroutines are so incredibly useful, and there’s so much yet-unexplored potential for game design purposes, so thank you JetBrains! The select part of the library seems experimental and little spoken of, so I wanted to talk about it a bit, and maybe where my needs are differing from what’s provided. Here’s an example script taken...

Setting fillStyle on Canvas using new WASM issue I am trying to set fillStyle on a HTML Canvas using the new KotlinWASM. If I pass a string - I get a compiler error. If I force it to Dynamic (to pass typing), I get the browser crashing say the passed value is opaque. * Compile Error (when String is passed)* file😕//Development/wasmMandlebrot/src/wasmMain/kotlin/canvas.kt:9:42 Type mismatch: inferred type is String but Dynamic? was expected Browser Error (when Dynamic is passed) Uncaught (in promise) TypeError: WebAssembly objects are...

Typealias with generic Let’s say I have a class container like this: class Container Then I have a handler like this: interface Handler{ fun map(c:Container):Pair fun add(c1:Container, c2:Container):Pair } Later I want to add another generic to container and handler, let’s call it F. Or i want to remove B and C from container and handler. Currently I have to make change at multiple places of the code, but I would like to have an opportunity to change the code not so often. Like to create a typealias in handler:...

`@PublishedAPI private fun` Why does @PublishedAPI only work for internal functions? I have a file-private function I want use from an inline function. I need to make it internal in order to work with @PublishedAPI. But I don’t want to expose this function to the rest of the module. I understand this has to do with java interoperability. This is a complex topic for me since I write 100% kotlin now, and never have to deal with java. In <a...

Kotlin idiomatic implementation of I have written the following function to find a histogram median. The loop with an external running total looks ugly compared to other more kotlin-esque code. Is there a way to make it more ‘elegant’ without compromising performance? I suspect that there is a function on collections that might do this, but I am not sure which. I would like to be told of it and how to use it… that is the way I learn. /** * Assuming that the receiver is a histogram where the value at each index is the count...

Eliminate redundancy of context receiver when overriding a function Hi all, What do you think of eliminating the redundancy of context(Scope) when overriding a function that already have it? In this snippet, wouldn’t it make more sense if we were able to just override performAction without explicitly adding context(Scope)? 1 post - 1 participant Read full topic

"DataType" for only initial null value For various reasons I work with classes which contain variables for objects which only can be null if not initialized. I would like this as an option to declare. class Hull { var nodeHullOptions: List? = null private set } I would suggest a third option: Do not allow to assign null again, maybe mark it with an additional exclamation mark: class Hull { var nodeHullOptions: List?! = null private set } The compiler can then do all the same checks it would do...

Do I need to know JAVA to get started in KOTLIN? On the website android.com it says that the minimum requirement to study and start programming in kotlin is to know JAVA, C ++ related language for at least 2 years. Why do you only have a notion of programming, what does the person do, learn JAVA and then KOTLIN or learn KOTLIN directly? Android Developers <a...

External Interface Required Fields When using Kotlin JS with libraries such as react, you may frequently create external interfaces for react props you want to use. They have to be external interfaces because they extend the external interface Props and Kotlin doesn’t like to extend external stuff with internal classes/interfaces.The problem is that if you want to specify required fields you have to essentially create a function wrapper to enforce which fields are required. In Typescript, using their equivalent to external...