java.lang.ClassCastException: service.CityName cannot be cast to java.lang.String

in Kotlin 1.3.10 with inline classes. I heard this is resolved but that Kotlin update isn't released yet. When will it be released? Or can I use the dev build with Gradle somehow? 🙂

no, I don't use String anywhere

So assigning an

inline class

instance returned by a generic (

reified

) function directly to a variable captured by a lambda seems to be problematic.

I want to declare a list that holds KClasses that extend Event, something like this:

List<KClass<? extends Event>>

I can't figure out what the right syntax for this is though, can someone help?

Still wrestling with generics. Is it possible to do this simple event handler?

class EventManager{
    private val listeners: MutableMap<KClass<out Event>, MutableList<EventListener<in Event>>> = HashMap()

    fun <T : Event> register(event: KClass<out T>, listener: EventListener<T>) {
        val eventListeners: MutableList<EventListener<T>> = listeners.getOrPut(event) { ArrayList() }
        eventListeners.add(listener)
    }

    fun notify(event: Event) {
        listeners[event::class]?.forEach { it.handle(event) }
    }
}

My

getOrPut

call wants a

MutableList<EventListener<T>>

but found

MutableList<EventListener<in Event>>

instead.

listOf(1, 2, 3).slice(0..5) Instead of getting an ArrayIndexOutOfBoundxException, how can I get (1, 2, 3)

Is changing a

public fun

to

public inline fun

binary and source compatible?

It should be source-compatible as long as only Kotlin is calling it. But it won’t be binary-compatible, as the method signature will only exist in the source. The compiler literally just replaces the method call with the body of the method, and leaves no trace of the original method.

I am trying to make simple json parser which will use jsonObject and JsonArray but firstly I need to create classes instance genericly

You need to look at the constructors via reflection.

Coming from Python/Smalltalk backgrounds, I really like explicit self receivers. Kotlin allows me to continue to be explicit (optionally) using

this

. For the grins of it (because sometimes silly ideas lead to better understanding), I thought I’d try something like this:

val <Receiver>Receiver.self: Receiver get() = this

It works pretty well. I can now use

self

in lieu of

this

. Except in a few cases. One such case is in an

init

block: private val manager:DownloadManager init { self.manager = self.context.getSystemService(Context.DOWNLOAD_SERVICE) as DownloadManager } It will not allow the

self.manager

reference there. It’s OK with the

self.context...

. And I can use just

manager

or

this.manager

, but for some reason my “selfish substitution” does not work there. Enlighten me?

in kotlin is it more idiomatic to define a var* with a custom getter and setter for persisting a value or defining methods for both to be explicit about the persistence going on

My Kotlin compiler is still crashing... I was hoping this would be sorted out after 1.0, but it's well into 1.3 now with no sign of stability. Is there ever going to be a stability release?

Good evening. Is there anyone out there using Eclipse, Kotlin and Gradle? I'm trying to find a way to get the Gradle Plugin to reference two Projects. Is it possible? I've googled and followed a LOT of articles, but keep hitting brick walls

Oops. I just tried to define a function like this:

fun isBetween(x, edge1, edge2): Boolean = x in (edge1 .. edge2)

but that doesn't Do What I Mean because

5 in (10 .. 1)

is false. Is there anything in the standard library that handles this already, or do I have to add an

if edge2 < edge1

in there to make sure they're the right way around?

Quick quesiton, so

findViewById

is no longer necessary,

val btnSaveClick= findViewById<Button>(R.id.btnSave)
      btnSaveClick?.setOnClickListener {
          Toast.makeText(this@ArticleAdapter, "Article saved.", Toast.LENGTH_LONG).show()
      }

What should be used instead

Is there a way to enable unsigned types module wide? To avoid having to put @UseExperimental on everything.

Hello, I want to use NonNull/Nullable annotations for Java code, but I heard that javax.annotation.NonNull/Nullable will be removed in the future. Then, which NonNull/Nullable annotation is recommended?

You want to implement

V

, an type not known at compile time?

hi there, what is the best way to solve that problem?:

open class ParentFoo
class ChildFoo : ParentFoo()

abstract class ParentBar {
	open var foo: ParentFoo? = null
}
class ChildBar : ParentBar() {
	override var foo: ChildFoo?
		get() = super.foo as ChildFoo?
		set(value) {
			super.foo = value
		}
}

right now I'm not allowed to set

ChildFoo

as the `ChildBar`'s

foo

property type as it is not exactly the same type as its parent's

foo

, but as it doesn't have a backing field I think this should be able to compile without any problem. What am I missing there?

In the last AoC challenge you have to put marbles in a circle (linked list), sometimes moving back 7 places from the current position. Stripped version of the my code for that is below. I thought that the straight forward

current.prev.prev.prev.prev.prev.prev.prev

should be the fastest way possible, but out of curiosity I also did it as

generateSequence(current) { it.prev }.take(8).last()

and to my surprise, when I measured times of execution I got this : -

.prev

chain -> 2389ms -

generateSequence

-> 460ms So why is

generateSequence

5 times faster? On my machine I get results like that when looping up to 10mln, after that

generateSequence

suddenly takes 3s to finish.

Is there a way I can disable synthetic property extensions generated for getter methods of java classes? I want to define my property extension having a name conflicting with the original getter method of the java class.

What type should I be putting in

???

such that

toResult

won’t error? I’ve tried

Nothing

and it is not working

sealed class ApiResult<T>

data class Success<T>(
    val msg: String,
    val data: T
) : ApiResult<T>()

data class Failure(
    val error: String,
    val errMsg: String
) : ApiResult<???>()

fun toResult(): ApiResult<User> {
        return if (error == "0") Success(
            msg = msg, data = movies
        ) else Failure(error = error, errMsg = errMsg)
    }

Is there a function akin to

uncurry

in kotlin? That is, a function which takes a function of two arguments and returns a function which takes a single pair of arguments?

Is it possible to create a static extension function to a Java class? It doesn't have a Companion to attach it to, but the non-static version is genericized?

yeah maybe…but in that case

putAll

and

put

have that same uncertainty

is their syntactic sugar around

if (a != null && b != null ) {

like there is with

a?.let {

?

also, does kotlin have Traits

Say I have a method A that returns a boolean, and a second method B that returns a nullable object. Is there a way with contracts that I can have it so if method A returns true, method B is known to be not null?