Is it possible to suppress the

NAME_SHADOWING

warning in Kotlin, globally? If not, where would I file a request for this feature?

Just a hint for every

Kotlin

programmer: you are pretty able to write

Scala

as well 🙂 Decided to shift to FP, and realized that

JetBrains

prepared me for that stuff somehow ❤️

With regards to type arguments for a function, is there a way not to have to specify all three when calling this function? https://pl.kotl.in/kMoCgjgsg That would be a very handy utility function to have for our codebase but having to specify superfluous type arguments undoes the value.

Hi, I try to make a Builder in Kotlin, all was fine with this sample code I inspirate from, but my goal is to consume it in Java (Kotlin default parameters = Overload methods), so the Builder pattern in Kotlin is not usefull to use in Java with this sample code. what alternatives I have ?

Hi folks, I'm trying to create a data type aking to

Result<T>

but which 1) Can return an arbitrary type as error and 2) Doesn't have a success payload. Here's the solution I came up with. I wonder if it can be expressed more elegantly?

sealed class EmptyResult<E> {
    class Success<E> : EmptyResult<E>()
    data class Failure<E>(val error: E): EmptyResult<E>()
}

fun foo(): EmptyResult<String> = EmptyResult.Success()

Hey folks, I might be missing something, but why IDE is not complaining about unsafe cast if following snippet?

val nullableList: List<String>? = listOf()
val nonNullableList: List<String> = nullableList as List<String>

I can't have private interface vals / functions even if everything is declared in the same file... right?

What does kotlin community thinks on this? Continue stuttering like in Java(2nd) or time to stop (1st)?

Anyone knows a proper way to make this compile (without unsafe casting)?

fun <T: Any> register(c: KClass<T>, i: T) {}

fun main() {
  listOf(ArrayList::class, LinkedList::class).forEach { // any different classes here
    register(it, it.createInstance())
  }
}

how stable is kotlin.time? Can I use it without fear of massive change or rather it's better to use something else 😄

Is there any way to get more info about an internal Kotlin compiler error other than the stacktrace that is printed? Like which line in the project caused the compiler error perhaps?

Do I miss something or type inference is confused here? A. Works

interface I

class Main : Base<MainParam<*>>
class MainParam<T : I> : BaseParam

interface Base<T : BaseParam>
interface BaseParam

B. Doesn't (

Type argument is not within its bounds

)

interface I

class Main : Base<Main.MainParam<*>> {
    class MainParam<T : I> : BaseParam
}

interface Base<T : BaseParam>
interface BaseParam

So this compiles but doesnt work as I expected at all, why?

Hello everyone, I am getting a very strange issue when testing my Kotlin code. The following code:

val lexer = // an instance of LixyLexer, line 180
val exc = assertFailsWith<LixyException> {
    lexer.tokenize("....")
}
assertNotNull(exc.message)
assert(exc.message!!.contains("token ends"))

causes this exception:

java.lang.VerifyError: JVMVRFY027 récepteur incompatible avec la classe déclarante; classe=guru/zoroark/lixy/LixyTest$Lixy incoherent matcher results cause exception (end is too far)$lexer$1, méthode=invoke(Lguru/zoroark/lixy/LixyDslEnvironment;)V, pc=26
Exception Details:
  Location:
    guru/zoroark/lixy/LixyTest$Lixy incoherent matcher results cause exception (end is too far)$lexer$1.invoke(Lguru/zoroark/lixy/LixyDslEnvironment;)V @26: JBinvokevirtual
  Reason:
    Type 'guru/zoroark/lixy/LixyTest$Lixy incoherent matcher results cause exception (end is too far)$lexer$1$1' (current frame, stack[1]) is not assignable to 'guru/zoroark/lixy/LixyDslEnvironment'
  Current Frame:
    bci: @26
    flags: { }
    locals: { 'guru/zoroark/lixy/LixyTest$Lixy incoherent matcher results cause exception (end is too far)$lexer$1', 'guru/zoroark/lixy/LixyDslEnvironment', '[Z' }
    stack: { 'guru/zoroark/lixy/LixyDslEnvironment', 'guru/zoroark/lixy/LixyTest$Lixy incoherent matcher results cause exception (end is too far)$lexer$1$1' }
	at guru.zoroark.lixy.LixyTest.Lixy incoherent matcher results cause exception (end is too far)(LixyTest.kt:180)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    (...snip...)

However, I am unable to replicate this on my CI environment, everything works fine there... Any ideas?

Did I imagine it, or is there some way to build a list using the Function literals with receiver, like typesafe DSLs do, so you can do something like this:

val myList = listOf {
    add("Blah")
    add("Foo")
    if(somethingIsTrue) {
         add("More")
         add("Stuff")
    }
}

I seem to remember somebody talking about it, or tweeting about it? Possibly it was coming to the standard libraries?

Is there any different between

top level variable

and

local variable

?

val outer = 1

fun main() {
    val inner = 2
    
    println(::outer.name) // outer
    println(::inner.name) // [References to variables aren't supported yet]
}

I'm confused why

println(::inner.name)

throws error 😕

OOP design question: Problem: I have a GOD class in my project which consist of more than 40 to 50 functions which belongs to different services. What I want to achieve: I want to move unique functions to dedicated subclasses and common functions to a parent class. Now the GOD class is injected in many classes. Can someone suggest me a design pattern where I don’t have to individually inject all these

SubClass

but a factory which will give the instances of these

SubClasses

and also provide access to the common functions which are in the parent class. Is it possible?

class GodClass {
    fun common(){}
    fun a(){}
    fun b(){}
    fun c(){}
    fun d(){}
}

abstract class ParentClass {
   fun common(){}
}

class SubClass1: ParentClass {
    fun a(){}
}

class SubClass2: ParentClass {
    fun b(){}
    fun c(){}
}

Should the thing mentioned here be reported as a bug? https://stackoverflow.com/questions/59822125/kotlin-variable-initialization-for-child-class-behaves-weird-for-initializing-va

I believe the Jvm kotlin compiler can target 8, right? Are there any plans to target more "modern" versions anytime soon?

Did anyone integrate a kotlin REPL into one of their apps, for debugging state of an application?

whats the best way to chain null checks. Say I had the following

val configuration = if (config != null) config else
        {
            val retrieved = configRepo.findByMerchantId(id)
            if (retrieved != null) retrieved else MerchantBillConfig(id, emptyList(), CurrencyIso("XXX"), false)
        }

I mean if a value is passed use that else try to retrieve one else generate a default one.

kotlinx.coroutines.async(context, start, block)

appears to be deprecated. What am I supposed to replace it with? I want to put

async(start=LAZY) { someSuspend() }

in my code, but I also don’t want to use deprecated functions. Technically I’m updating some third-party library’s documentation, and I’d rather my PR not use deprecated methods. The current sample code uses

async {…}

and I’d rather not dramatically alter the sample code, but hew closely to the original.

I am very confused. I'm trying to override a spring batch provided class method, but it is having signature issues. I am not sure, but I'm assuming I'm supposed to return null when null otherwise it's not up to spec(perhaps "" will work, but that's not the cleanest solution). Why won't it let me make it a nullable String, when the method it is overriding is java.lang.String in a java source code? How do I get around this? (parameter being nonnull string is also another signature issue - if I make it a nullable string, it says it has nothing to override because of signature mismatch, yet... source reveals it's a plain java string that isn't annotated otherwise)

I have a data class with some fields of enum type and some are just Strings. I need to create an object with just one String field and thus not include enum fields. How should I declare enum fields in my data class so that they will have an empty default value?

when should i use a type alias, when an inline class and when just the underlying type? example: i'm developing something like an instant messager and each message has a unique ID (which at the end of the day is just a

Long

) and i figured it might be worth using a typealias or inline class to clarify that using this number for e.g. multiplication makes no sense. if possible, I am looking for a generalized answer so I know how to make this decision myself in the future

Is there a way to easily switch between different versions of the Kotlin plugin. Say I want to test out a plugin in EAP channel and then revert to a stable channel plugin. Right now will have load plugin from disk to downgrade.

What collections extension function can I use if I want to get first element from the list and if list is empty, then run a function that creates an element and returns it? The closest I found is

ifEmpty{}

, but it returns the entire collection if it is not empty, while I don’t need the collection and just it’s first element.

is there any proper way to create abstract factory functions to force their implementation? I have an abstract class

Packet

(for networking) that needs a

serialize

and

deserialize

function. the former is easy, just a regular abstract function with a

ByteWriteChannel

param to write the packet into. the latter however needs to be either a top-level extension function for

ByteReadChannel

or in the companion object, neither of which allows the

abstract

keyword (obviously). how do I ensure that each

Packet

class implements a

deserialize

factory function ?

Any documentation or information on writing SDK ? Patterns, architecture, best pratice...