Has the

let

function always been callable on nullable types (ie not

<T : Any>

)? I could have sworn that the following didn't use to work:

fun foo(s: String?) {
    s.let { } // <- expected I had to do s?.let { }
}

Has it always worked like this or was this changed at some point?

Hi guys, I don't quite understand some use cases of generics within stdlib and how they work. Example:

public inline fun <R, T : R> Result<T>.getOrElse(onFailure: (exception: Throwable) -> R): R

From the signature I would think that since

T

is of type

R

or its subtype, on

Result<SubClass>

instance I could invoke

getOrElse

only by passing lambda returning value of type which is super type to

SubClass

. Below code compiles perfectly fine, and I'm not sure why:

val x: Result<CharSequence> = runCatching { "string value" }

val z = x.getOrElse { 123 }

it would be logical for me that only lambdas returning super type of

CharSequence

should be accepted, but I can pass whatever return type I want and this still works fine, it just makes inferred type of

z

Result<Any>

. Am I missing something or should this not be expected behavior? Also, I cannot understand reason behind

T : R

within function's declaration, if anything

R : T

would be more logical to my understanding.

Anyone got an idea how to make this work? Basically the function’s type parameter

Interface

needs to be a supertype of the class’s type parameter

Implementation

.

What is the use of providing named parameters in lambda types, this doesn't get used instead of 'it' so what is the actual use here, am i missing something?

I found myself a couple of time in the case where, given a list of string, I want to drop everything until a specific line, including the line itself, that is

dropWhile { it != line }.drop(1)

Is there a better way to do this?

Is there any possiblity to smartcast/return the same subtype of a sealed class when using it as receiver and when?

sealed class F {
  object A: F()
  object B: F()
}
fun F.foo(): F = when (this) {
  is F.A -> F.A
  is F.B -> F.B
}
val a: F.A = F.A.foo() // not possible without a cast

no

note

tag in kdoc?

coming from Rust: does Kotlin

sequence

have an equivalent of Rust’s

.next()

for `Iterator`s, which (lazily) returns the next item in the sequence if there is one, or

null

otherwise?

Hi, all. Im’ pretty new to using Kotlin. I’m looking for a good tutorial for how to build a cross-platform (iOS, Android) user interface for an app I’m tinkering with. Any suggestions?

Hello, I am just starting to learn Kotlin and am practicing on Intellij - I am trying to make Dog objects from a class and am having a horrible time trying to figure out how to use fun main() with the class declaration. Would someone explain to me please where I put the class methods and properties etc. when I using main(). I know there must be some logic behind this but I am tired of getting "Expecting member declaration". I would appreciate any help!

since extension functions aren't allowed on enum entry names, what is the better approach to implement this?

@Suppress("EnumEntryName")
enum class ConfigUri(val raw: String) {

	login("/login"),
	logout("/logout"),
	register("/register"),
	verify("/verify/{hash}"),
	reset1("/reset"),
	reset2("/reset/{hash}")
	;

	fun verify.build(hash: String): String = raw.replace("{hash}", hash)

}

in the endpoints where I declare the GET / POST handlers, I want to be able to do

GET(ConfigUri.login.raw)

and in places where I need to fill in the hashes for example when sending out an email with a verify link, I want to be able to do

ConfigUri.verify.build(hash = generatedRandomHash)

to generate something like

/verify/12344-1324234-sdfsdfs

Hi all, any one having trouble building/running the default hello world sample code, created by Intellij when creating a kotlin project?

In my installation, java hello world sample is running right of the bat as it, while kotlin sample hello world is complaining "No JDK Specified". i checked Project Structure, things seemed ok there. What could be wrong?

Resolved, but the default sample code project seems to have set the default sdk as "Kotlin SDK" in Project Settings. After changing it to the JDK in project settings the program is compiling and running.

Shouldnt the setting be JDK by default than "Kotlin SDK", as this could be confusing to people...

Is there really a Kotlin SDK now or is it only the Kotlin Plugin? But some places in the IDE like the Project Structure seems to still refer to a 'Kotlin SDK'.

Is it possible to create an extension function on functions?

Hi, all. I’m starting work on an app, targeting iPads and Android tablets. My question is with dependency injection. I have a service class (OPDSLibraryService) that I would like to have automatically injected into other classes as needed, similar to how Spring’s @Autowired works. Is that an option working with Kotlin and KMM and, if so, can someone point me to a tutorial on how to get that working?

Should this be allowed? It does compile fine if I remove the type annotation from

acceptsString

I want to say

R

can be constrained to

String

by the smart cast but I'm not sure.

interface Accepts<in T> {
    fun accept(value: T)
}

object AcceptsString : Accepts<String> {
    override fun accept(value: String) = println(value)
}

fun <R> example(providesR: () -> R, acceptsR: Accepts<R>) {
    if (acceptsR is AcceptsString) { // so R must be String
        val acceptsString: AcceptsString = acceptsR
        val providedR = providesR()

        acceptsString.accept(providedR)
        //                   ^^^^^^^^^ Type mismatch.
        //                             Required: String
        //                             Found: R
    }
}

if I’ve got a function with a

List<String>

, can I expect Kotlin to reuse this list, or will it allocate on every call to the function?

Hi 🙂 kind of new in Kotlin i am using the https://github.com/fabric8io/kubernetes-client and i trying to create a fun to wait until all pods are ready so i first took all the names of the pods

private fun printAllPodsName() {
    val podList = client.pods().inNamespace("default").list()
    podList.items.forEach(Consumer { obj: Pod ->
        println(obj.metadata.name)
    })
}

now i want to go over this pod name list so it will check if the status is ready or not i tried to do something like this

fun waitUntilAllPodsAreReady() {
        for (podname in printAllPodsName().toString()) {
            client.pods().inNamespace("default").waitUntilCondition({ pods ->
                pods.status != null && pods.status.conditions != null
            }, 10, TimeUnit.MINUTES)
            println(podname.toString())
        }
    }

but it seems like not working any idea will be blessed

Hi all! please tell me why? Spring Boot Applcation Main class (for start) can not start, application

@SpringBootApplication
class ApiApplication {

    fun main(args: Array<String>) {
        runApplication<ApiApplication>(*args) {
            setBannerMode(Banner.Mode.OFF)
        }
    }
}

and this work! why?

@SpringBootApplication
class ApiApplication {

    companion object {
        @JvmStatic
        fun main(args: Array<String>) {
            SpringApplication.run(ApiApplication::class.java, *args)
        }
    }

}

Is there a difference between an enum and a sealed interface that only contains objects? I wonder if sealed classes/interfaces make enums obsolete.

Can someone explain why kotlin compiler (or ide?) differentiates between these types of bugs? This was a problem for us

is it possible to make a class property that only the class itself can mutate, but is public to other classes? without making a getter? I expected

private set

to do this, but it seems like I can still mutate the value from outside the class.

Hi, is there some way we can define a variable with "-" ? sometimes json data from request may has some field name with "-", how to defined a correspond variable in data class ? the json data could be

{ "refresh-token" : "some thing" }

I got error like this:

Hi i am trying to use this fun to run a linux command inside a k8s pod using fabric8io kubernetes client

fun execIntoContainer(podName: String, containerId: String, cmd: String) : String {
    val future = CompletableFuture<Int>()
    val listener = CompletableExecListener(future)
    val out = ByteArrayOutputStream()
    val error = ByteArrayOutputStream()
    val command = cmd.split(" ").toTypedArray()
    val exec = kubernetesClient.pods().withName(podName).inContainer(containerId)
        .writingOutput(out)
        .writingError(error)
        .usingListener(listener)
        .exec(*command)
    future.get(10, TimeUnit.SECONDS)
    exec.close()
    if (error.toString().isEmpty()) {
        return out.toString()
     }
        throw RuntimeException("Error from pod: $error")
    }

it seems works just for one command. when i add a grep for example (ls -ltr | grep t) it gave me an error and seems like the issue is with the split part

cmd.split(" ").toTypedArray()

org.opentest4j.AssertionFailedError: Unexpected exception thrown: java.lang.RuntimeException: Error from pod: ls: cannot access '|': No such file or directory
ls: cannot access 'grep': No such file or directory
ls: cannot access 't': No such file or directory

any idea how can i use the split?

How can I get around

Overload resolution ambiguity

for a function that has two

varargs

single-argument signatures?

Overload resolution ambiguity. All these functions match.
public open fun <T : Any!> array(vararg values: TypeVariable(T)!): Field<Array<(out) TypeVariable(T)!>!> defined in org.jooq.impl.DSL
public open fun <T : Any!> array(vararg fields: Field<TypeVariable(T)!>!): Field<Array<(out) TypeVariable(T)!>!> defined in org.jooq.impl.DSL

It works in Java, but not in Kotlin. I can't use

null

or `emptyArray()`/`emptyList()` because that produces the wrong results =/

hello , how do I contribute to kotlin projects on GitHub without building or running tests on my local machine ? especially when I have to make sure my code does not beak anything else ?

Hello, I’m trying to use

limitedParallelism

on Dispachers.IO but it is nowhere to be found despite me being on kotlinx coroutines 1.6.4. Am I missing something?