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announcements

Jayden

12/09/2019, 10:14 PM

How do people normally name files that only contain extensions? 1. ViewExtensions.kt 2. ViewExt.kt 3. ?

2️⃣ 3

1️⃣ 9

3️⃣ 7

girafferson

12/10/2019, 3:40 AM

I'm not sure which channel this would be most relevant in. Does anyone know why my androidTest isn't building? I have

android {
  defaultConfig {
    testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner
}}

Joey

12/10/2019, 5:36 AM

Hi guys, what is the best way to return a

List<String>

from a coroutine? My current code is this one but its kinda slow and affects my UI in android

fun fetchUsers(): List<String> {
    val heartbeatApi = HeartbeatApi()
    val users = runBlocking {
        withContext(Dispatchers.Default) {heartbeatApi.fetchUsers() }
    }
    return users
}

Ashutosh Panda

12/10/2019, 7:48 AM

class book(){
    var pages:Int=300
}
class puppy(b: book)
{
    fun removePages():Int=b.pages-Random().nextInt(0,100)
}

fun book.getWeight():Double=pages*1.5
val hamlet=book()
val puppy=puppy(hamlet)
fun book.CountPages(i:Int):Int=pages-i
println("${hamlet.CountPages(20) } \n")
println("${hamlet.getWeight()} \n")
println("${puppy.removePages()+hamlet.CountPages(20)}")

Hoanghun5

12/10/2019, 12:50 PM

Hello, I got an assignment to benchmark Java vs Kotlin. I was thinking I could benchmark Collections insert and remove speed such as ArrayList.add. Is it a good idea or does Kotlin just use internally Java colletions? If so, what else could I benchmark to show difference between Java and Kotlin?

eekboom

12/10/2019, 2:07 PM

While debugging: Is there a way to break on a property access? My workaround is to add a get() just for the sake of debugging while I need it :-(

Kris Wong

12/10/2019, 4:53 PM

how do I return/break to the next loop iteration

loop@ for ((key, value) in jsonEvent.getObject("properties").content) {
    when (value) {
        is JsonArray -> {
        }
        is JsonPrimitive -> {
            value.booleanOrNull?.let {
                event.properties[key] = it
                return/break??
            }
        }
    }
}

pniederw

12/10/2019, 8:18 PM

I wish

when

had better smart casts. I'm often hitting this case:

open class Animal
class Cat : Animal()
class Dog : Animal()

when (any) {
  is Cat, is Dog -> // I wish `any` had type `Animal` here, not `Any`
}

Slackbot

12/10/2019, 10:02 PM

This message was deleted.

ShootingStar

12/11/2019, 12:41 AM

In a Kotlin project with the gradle build, Is there a usecase to use a

java-library

plugin even though I already use kotlin gradle plugin?

Aiden

12/11/2019, 3:10 AM

Can I know where can I learn more about NoSQL?

KyooSik Lee

12/11/2019, 9:20 AM

Hello I am pretty new to Functional Programming of Kotlin. I am currently using Reactor for my project It is difficult to work in streams because once the instances of the stream changes it form, I can’t use the instances before change. ex) • Flux<AClass> -> Flux<BClass> -> SomeFunction that needs instances of AClass If above situation happens, I had to find AClass instances again, so the stream would go like • Flux<AClass> -> Flux<BClass> -> Flux<AClass> which I think is redundant and DB-work-expensive So I came up with this Idea to store the value of AClass, and then use it later without getting back.

fun someFunction(something: Foo): Mono<Foo> {
        var zoo: Foo = Foo();

        fooRepository.find()
                .doOnNext { zoo = functionThatReturnsZoo() } // change the value of zoo
                .flatMap { ... }
                .flatMap { fooRepository.save(zoo) } // use zoo
    }

Will this be functional too?

XQDD

12/11/2019, 9:29 AM

Why It becomes null when running in java

trathschlag

12/11/2019, 12:48 PM

Nested, suspendable tailrec extension-functions (don't ask :)) seem to upset the compiler:

fun test() {
    tailrec suspend fun Int.handle(): Int {
        return when {
            this <= 0 -> 0
            else -> (this - 1).handle()
        }
    }
}

:youtrack: 1

trathschlag

12/11/2019, 12:48 PM

e: org.jetbrains.kotlin.codegen.CompilationException: Back-end (JVM) Internal error: Failed to generate expression: KtNamedFunction
File being compiled at position: [...]
The root cause java.lang.AssertionError was thrown at: org.jetbrains.kotlin.codegen.context.MethodContext.getReceiverExpression(MethodContext.java:66)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.genQualified(ExpressionCodegen.java:324)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.genStatement(ExpressionCodegen.java:407)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.generateBlock(ExpressionCodegen.java:1269)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.generateBlock(ExpressionCodegen.java:1214)
	at org.jetbrains.kotlin.codegen.CodegenStatementVisitor.visitBlockExpression(CodegenStatementVisitor.java:56)
	at org.jetbrains.kotlin.codegen.CodegenStatementVisitor.visitBlockExpression(CodegenStatementVisitor.java:22)
	at org.jetbrains.kotlin.psi.KtBlockExpression.accept(KtBlockExpression.java:78)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.genQualified(ExpressionCodegen.java:302)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.genStatement(ExpressionCodegen.java:407)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.gen(ExpressionCodegen.java:364)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.returnExpression(ExpressionCodegen.java:1701)
	at org.jetbrains.kotlin.codegen.FunctionGenerationStrategy$FunctionDefault.doGenerateBody(FunctionGenerationStrategy.java:64)
	at org.jetbrains.kotlin.codegen.FunctionGenerationStrategy$CodegenBased.generateBody(FunctionGenerationStrategy.java:84)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethodBody(FunctionCodegen.java:666)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethodBody(FunctionCodegen.java:473)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethod(FunctionCodegen.java:260)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethod(FunctionCodegen.java:176)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.gen(FunctionCodegen.java:147)
	at org.jetbrains.kotlin.codegen.MemberCodegen.genSimpleMember(MemberCodegen.java:197)
	at org.jetbrains.kotlin.codegen.PackagePartCodegen.generateBody(PackagePartCodegen.java:95)
	at org.jetbrains.kotlin.codegen.MemberCodegen.generate(MemberCodegen.java:129)
	at org.jetbrains.kotlin.codegen.PackageCodegenImpl.generateFile(PackageCodegenImpl.java:148)
	at org.jetbrains.kotlin.codegen.PackageCodegenImpl.generate(PackageCodegenImpl.java:68)
	at org.jetbrains.kotlin.codegen.DefaultCodegenFactory.generatePackage(CodegenFactory.kt:96)
	at org.jetbrains.kotlin.codegen.DefaultCodegenFactory.generateModule(CodegenFactory.kt:67)
	at org.jetbrains.kotlin.codegen.KotlinCodegenFacade.doGenerateFiles(KotlinCodegenFacade.java:47)
	at org.jetbrains.kotlin.codegen.KotlinCodegenFacade.compileCorrectFiles(KotlinCodegenFacade.java:39)
	at org.jetbrains.kotlin.cli.jvm.compiler.KotlinToJVMBytecodeCompiler.generate(KotlinToJVMBytecodeCompiler.kt:637)
	at org.jetbrains.kotlin.cli.jvm.compiler.KotlinToJVMBytecodeCompiler.compileModules$cli(KotlinToJVMBytecodeCompiler.kt:195)
	at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecute(K2JVMCompiler.kt:165)
	at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecute(K2JVMCompiler.kt:55)
	at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.kt:84)
	at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.kt:42)
	at org.jetbrains.kotlin.cli.common.CLITool.exec(CLITool.kt:104)
	at org.jetbrains.kotlin.incremental.IncrementalJvmCompilerRunner.runCompiler(IncrementalJvmCompilerRunner.kt:349)
	at org.jetbrains.kotlin.incremental.IncrementalJvmCompilerRunner.runCompiler(IncrementalJvmCompilerRunner.kt:105)
	at org.jetbrains.kotlin.incremental.IncrementalCompilerRunner.compileIncrementally(IncrementalCompilerRunner.kt:237)
	at org.jetbrains.kotlin.incremental.IncrementalCompilerRunner.compile(IncrementalCompilerRunner.kt:88)
	at org.jetbrains.kotlin.daemon.CompileServiceImplBase.execIncrementalCompiler(CompileServiceImpl.kt:606)
	at org.jetbrains.kotlin.daemon.CompileServiceImplBase.access$execIncrementalCompiler(CompileServiceImpl.kt:99)
	at org.jetbrains.kotlin.daemon.CompileServiceImpl.compile(CompileServiceImpl.kt:1645)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)
	at sun.rmi.transport.Transport$1.run(Transport.java:200)
	at sun.rmi.transport.Transport$1.run(Transport.java:197)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
	at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:573)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:834)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:688)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:687)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.AssertionError
	at org.jetbrains.kotlin.codegen.context.MethodContext.getReceiverExpression(MethodContext.java:66)
	at org.jetbrains.kotlin.codegen.TailRecursionCodegen.generateTailRecursion(TailRecursionCodegen.kt:62)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.invokeMethodWithArguments(ExpressionCodegen.java:2511)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.invokeMethodWithArguments(ExpressionCodegen.java:2476)
	at org.jetbrains.kotlin.codegen.Callable$invokeMethodWithArguments$1.invoke(Callable.kt:41)
	at org.jetbrains.kotlin.codegen.Callable$invokeMethodWithArguments$1.invoke(Callable.kt:13)
	at org.jetbrains.kotlin.codegen.OperationStackValue.putSelector(StackValue.kt:79)
	at org.jetbrains.kotlin.codegen.StackValue.put(StackValue.java:122)
	at org.jetbrains.kotlin.codegen.StackValue.put(StackValue.java:115)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.putStackValue(ExpressionCodegen.java:384)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.gen(ExpressionCodegen.java:365)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.lambda$generateWhenExpression$36(ExpressionCodegen.java:5028)
	at org.jetbrains.kotlin.codegen.OperationStackValue.putSelector(StackValue.kt:79)
	at org.jetbrains.kotlin.codegen.StackValue.put(StackValue.java:122)
	at org.jetbrains.kotlin.codegen.StackValue.put(StackValue.java:115)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.putStackValue(ExpressionCodegen.java:384)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.lambda$visitReturnExpression$11(ExpressionCodegen.java:1612)
	at org.jetbrains.kotlin.codegen.OperationStackValue.putSelector(StackValue.kt:79)
	at org.jetbrains.kotlin.codegen.StackValueWithLeaveTask.putSelector(StackValue.kt:67)
	at org.jetbrains.kotlin.codegen.StackValue.put(StackValue.java:122)
	at org.jetbrains.kotlin.codegen.StackValue.put(StackValue.java:115)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.putStackValue(ExpressionCodegen.java:384)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.gen(ExpressionCodegen.java:365)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.returnExpression(ExpressionCodegen.java:1701)
	at org.jetbrains.kotlin.codegen.FunctionGenerationStrategy$FunctionDefault.doGenerateBody(FunctionGenerationStrategy.java:64)
	at org.jetbrains.kotlin.codegen.coroutines.CoroutineCodegenForLambda$generateResumeImpl$1.doGenerateBody(CoroutineCodegen.kt:498)
	at org.jetbrains.kotlin.codegen.FunctionGenerationStrategy$CodegenBased.generateBody(FunctionGenerationStrategy.java:84)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethodBody(FunctionCodegen.java:666)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethodBody(FunctionCodegen.java:473)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethod(FunctionCodegen.java:260)
	at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethod(FunctionCodegen.java:176)
	at org.jetbrains.kotlin.codegen.coroutines.CoroutineCodegenForLambda.generateResumeImpl(CoroutineCodegen.kt:464)
	at org.jetbrains.kotlin.codegen.coroutines.CoroutineCodegenForLambda.generateClosureBody(CoroutineCodegen.kt:239)
	at org.jetbrains.kotlin.codegen.ClosureCodegen.generateBody(ClosureCodegen.java:169)
	at org.jetbrains.kotlin.codegen.coroutines.CoroutineCodegenForLambda.generateBody(CoroutineCodegen.kt:247)
	at org.jetbrains.kotlin.codegen.MemberCodegen.generate(MemberCodegen.java:129)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.genClosure(ExpressionCodegen.java:1031)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.genClosure(ExpressionCodegen.java:1001)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.visitNamedFunction(ExpressionCodegen.java:973)
	at org.jetbrains.kotlin.codegen.CodegenStatementVisitor.visitNamedFunction(CodegenStatementVisitor.java:46)
	at org.jetbrains.kotlin.codegen.CodegenStatementVisitor.visitNamedFunction(CodegenStatementVisitor.java:22)
	at org.jetbrains.kotlin.psi.KtNamedFunction.accept(KtNamedFunction.java:50)
	at org.jetbrains.kotlin.codegen.ExpressionCodegen.genQualified(ExpressionCodegen.java:302)
	... 57 more

Brian Estrada

12/11/2019, 1:32 PM

I know this isn’t kotlin related but anyone here good with regex that can help me out?

silvio

12/11/2019, 1:48 PM

Why are Exceptions in Kotlin always unchecked? Wouldn't this lead to a lot of programming errors?

John

12/11/2019, 3:54 PM

Has anyone found a way to pass a lambda in a Serializable object?

Or Cohen

12/11/2019, 4:26 PM

Hi guys. I guess this is more of a Gradle related question but I’m just gonna post it here hoping for some sort of advice. Did anyone experience configuring (and working on) a monorepo containing multiple libraries? Lets assume that these libs can depend on one another AND and can also appear as dependencies in other projects (in other repos). This means that I wanna be able to: 1. Build the artifacts that are contained inside this mono repo in a way that’ll respect my dependencies. Assuming I have three libraries called A, B and C, while A depends on B and C is entirly independent, I wanna build both B and A in case there’s a change in B, but I don’t want C to be built) 2. Publish all artifacts that were changed during the build process to a local artifactory, later to be consumed by other components stored in different repositories I can share some more info on DM if needed, for example the tools used in my organisation with which I wanna achieve what I mentioned above. I encountered Gradle’s composite builds and multi-project builds but I’m still not quite sure about the differences and what fits better for my needs. Would appreciate any kind of help. Thanks in advance!

Pacane

12/11/2019, 10:20 PM

I'm preparing the object to be added to the database in another layer where my transaction happens, and therefore I can't use

MyEntity.new

in that layer, otherwise it complains that there's no transaction context.

Joseph PH

12/12/2019, 4:53 AM

Hello, is it possible in Kotlin to do returns based on the configuration? For example,

fun foo(useHttps: Boolean, conn: URLConnection): <Return type should either be HttpURLConnection/HttpURLsConnection> {
    // Logic here
    return URLConnection as HttpURLConnection/HttpURLsConnection // based on config?
}

tony

12/12/2019, 8:01 AM

are there any tools available to compute the ABI of a Kotlin class? I am working on a gradle plugin that does some dependency analysis, and one thing I'd like to be able to do is tell users whether dependencies should be

implementation

api

. To do that, I need to know the ABI of a set of compiled .class files. I'd like a tool like ASM, but for Kotlin. I have found https://github.com/JetBrains/kotlin/tree/master/libraries/kotlinx-metadata/jvm, which is interesting, but it seems like it currently requires an actual KClass instance, when ideally I could just feed it a byte array (as in ASM)

Alexjok

12/12/2019, 12:12 PM

Hello, why when i try do something like this it's doesn't compile reason: Incompatible types: String and Class<T>

class TypeClass<T>(
    private val returnResultAs: Class<T>
) {

    fun testCast(value: String): Result<Any, Exception> = when (returnResultAs) {
        is String -> Result.of { value }
        else -> Result.of { Gson().fromJson(value, returnResultAs) }
    }

}

But if i added

returnResultAs as Any

it works.

class TypeClass<T>(
    private val returnResultAs: Class<T>
) {

    fun testCast(value: String): Result<Any, Exception> = when (returnResultAs as Any) {
        is String -> Result.of { value }
        else -> Result.of { Gson().fromJson(value, returnResultAs) }
    }

}

Ashutosh Panda

12/12/2019, 1:03 PM

Hey can some one please explain me in type in generics

AdalPari

12/12/2019, 2:49 PM

Hi there! Are there any functional fun to iterate over a list and apply an operation to the current element with the previous one? It would be like a fold, but instead of accumulating the result, just applying it to each element. E.g:

(1..9).fold("a", { last, current -> last + current })

This just returns a123456789 but I actually need to create the following list: { "a1", "a12", "a123", "a1234", .. } I would be more like a map but knowing previous element:

(1..9).map { "$previousElement$it" }

Kris Wong

12/12/2019, 8:14 PM

IDEA all of a sudden seems to be really confused about my Kotlin/JVM project. it won't build or run it anymore. when I try it just does nothing.

Kroppeb

12/12/2019, 9:17 PM

The

::gcd

is referencing the

Iterable<Int>.gcd()

instead of

gcd(Int, Int)

. Swapping

::gcd

::helpers.gcd

gives

Unresolved reference: helpers

but renaming the function to something else and then back to

gcd

will swap it to

::helpers.gcd

which is marked red with

Internal Error occured while analyzing this expression

. How should I fix?

Untitled

Mehdi

12/13/2019, 12:51 AM

Does anybody know any useful library for invoking SOAP web services in Kotlin?

😱 4

😬 2

basher

12/13/2019, 2:19 AM

Any good blog posts about refactoring using Kotlin delegation or using Kotlin delegation that's not about properties? As an iOS developer, this is something I haven't quite wrapped my head around in terms of when I should use this tool compared to something else

Andreas Jost

12/13/2019, 9:15 AM

If I have to filter a list, is it always better (performance-wise) to convert it to a flow first or did I misunderstand something?

Title

Andreas Jost

12/13/2019, 9:15 AM

If I have to filter a list, is it always better (performance-wise) to convert it to a flow first or did I misunderstand something?

streetsofboston

12/13/2019, 9:40 AM

No, unless you really need a Flow, don't convert it to a Flow. Just keep it as a list and call

filter

on it. For large lists and if you call many operators on the list, you may want to convert it to a

Sequence

Also, avoid optimizing (early) if you don't see or experience a performance issue. 😀

💯 3

Andreas Jost

12/13/2019, 9:46 AM

Thanks, but flows/sequences would make sense if I had a larger list of data entities and want to map it to a list of domain entities, and might also filter afterwards, right? I will look up the difference between flow and sequence.

streetsofboston

12/13/2019, 10:03 AM

Flow is a (cold) stream of data. You'd need a Coroutine to collect the data emitted by a Flow. A Sequence is a 'lazy' view on a collection (list). No need for Coroutines.

➕ 1

Andreas Jost

12/13/2019, 10:05 AM

Understood, great explanation, thank you!

Matteo Mirk

12/24/2019, 9:36 AM

If it’s not a huge list, just call

list.filter {}

and be fine. I support what Anton said: don’t optimize prematurely, only if you experience a slow execution.

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