Hello! In my java code I have method

void test(Consumer<Test> consumer)

When I call it from kotlin

test{ it.doSmth() }

What should I do to be abble to call it from java like this

test{ this.doSmth() }

so it must behave as extension function lambda

I am the organizer of Kotlin community in Mumbai, India

are there any advantages using Optional rather than nullable type?

output like this:

val list = listOf("A", "B", "C")
var str = "";
list.forEachIndexed() {index , element ->
    str += " [$index:$element]"
}

i don't mean this condescendingly: what is the point of SAMs in kotlin? why not just write a top-level method? inheritance (guessing no)? java compatibility (guessing yes)?

Why does Kotlin compile

(Entity)->Boolean

to just a

Function1<Entity, Boolean>

and not to something that doesn't require boxing like `Predicate<Entity`>?

I want to create an annotation that can accept a param with different types.

annotation class Decimal(val value: Int)

I mean the

value

type could be for example,

Int

,

BigInteger

, or

BigDecimal

What do you think the best approach to do this?

I'm trying to pack an

Int

as a

Short

in the upper part of a

Long

, but I get an out of range on declaring an hexadecimal number

val l = (value.toLong() shl 48) and 0xffff_0000_0000_0000  // Error:(103, 42) Kotlin: The value is out of range. Expected: Long. Found: Int

How can I solve? Casting to

Long

doesnt help

shouldnt postfix

u

help maybe? (this works though

(0xffff shl 48)

)

Why does

foo.value

resolve to

Any?

and not the upper bound

Bar

?

Shouldn't foo be smart cast to non-null in the second condition?

Hello, World! Hey I was looking at contracts again (even though they're still experimental), and couldn't find a way to do what I want, so I'm wondering if it's possible. I have a

fun parseDate(dateStr: String?): Date?

and want to express that if

dateStr

is

null

then the result will be

null

- and also the opposite. Possible?

Hello, I want to know why the below code is throwing exception to the console even though i'm handling it using "CoroutineExceptionHandler"?

fun main() = runBlocking {

with(CoroutineScope(coroutineContext + CoroutineExceptionHandler { _, _ ->  println("Exception")})) {

val firstChild = launch() { // if i add "CoroutineExceptionHandler here, then launch coroutine will handle exception without printing on console

println("First child is failing")

delay(1000)

throw AssertionError("First child is cancelled")

}

// launch the second child

val secondChild = launch {

println("First child is cancelled: ${firstChild.isCancelled}, but second one is still active")

try {

delay(Long.MAX_VALUE)

} finally {

println("Second child is cancelled")

}

}

secondChild.join()

}

}

Hi all, I have question regarding annotations. Assume a following example

open class A(val strings: List<String>)

class B(strings: List<String>) : A(strings)

class C(strings: List<String>) : A(strings)

these classes are used in my REST API and I would like to validate their content with JSR annotations. I want to check that the collection

strings

in class

B

is not empty using

@NotEmpty

but I can apply this validation only on the property declaration (if I’m not mistaken). What is the best Kotlin way to add this validation to class

B

? In java I would probably override getter in class B and add annotation there, can I do something similar in Kotlin?

I guess this function would do

inline fun <reified T> listWith(count: Int, element: T): List<T> =
    Array(count) { element }.toList()

can someone confirm or correct my understanding of programming terminology? identifier: things that programmers can choose a name for object: (not the kotlin keyword specifically but in general) group of identifiers member: direct child of an object class: identifier that blueprints an object singleton: class that can only produce a single object which is accessed as if the class IS the object variable: identifier that stores a value field: member variable property: field with getter and setter attribute: vague term, does not have a unique definition function: identifier for which i dont find the right words to describe it method: member function lambda: nameless function closure: lambda that captures it's context

Hey guys! When talking about Kotlin libraries, there's a specific part in the code style that states

Always explicitly specify function return types and property types (to avoid accidentally changing the return type when the implementation changes)

It's kind of ambiguous for me if it applies to

Unit

as well. As I understand, it's meant for

fun test(someVar:String) = when(someVar){
 "a" -> 10
 else -> 20
}

where you can easily break the Int return. Would we always specify that a certain method returns Unit, even if it's redundant?

Is Kotlin an extension of Java or is it it’s own separate language?

Anyone else saw the above tweet? Not unpopular to me.

I'm trying to use

1.4-M1

and I'm getting this warning from gradle:

w: Runtime JAR files in the classpath should have the same version. These files were found in the classpath:
    /opt/rjaros/.gradle/wrapper/dists/gradle-6.3-all/b4awcolw9l59x95tu1obfh9i8/gradle-6.3/lib/kotlin-stdlib-1.3.70.jar (version 1.3)
...
    /opt/rjaros/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib/1.4-M1/1bd127486717887634cc406a5651bd6090f11678/kotlin-stdlib-1.4-M1.jar (version 1.4)
w: Consider providing an explicit dependency on kotlin-reflect 1.4 to prevent strange errors
w: Some runtime JAR files in the classpath have an incompatible version. Consider removing them from the classpath

Should I ignore this or somehow fix this?

Is there a way to find out and configure, which version of Kotlin does this language server uses? https://github.com/fwcd/kotlin-language-server

What does the new "delegate to another property" get you over a custom getter/setter?

Hi everyone! I want to be able to listen to changes on a variable and be able to publish new value to this variable. I’m wondering what would be the best thing to use without relying on RxJava (to use Subject) I’m torn between LiveData and ConflatedBroadcastChannel, any idea what the best one is?

A quick silly question, subjecting kotlinx.serialization: is it recommended to create one Json() instance and inject it throughout your project or create a new one on every use?

Something that’s always stumped me. Why do anonymous inner classes in Kotlin start with

object

? That seems to be a misnomer to me, and that it should be

class

instead. What am I missing?

Hey guys I'm trying to create an app and inside of my ViewModel I have firebase authentication and database set up inside of it. I'm having trouble with creating a callback for my UI. So what I'm trying to do is create an user in my viewmodel and once that's done return that success to my UI so that it can transition to the next activity. Is there a way to do this?

Due to the pandemic I find myself, as I'm sure lots of you as well, doing remote pairing or mobbing sessions. Zoom + IntelliJ give very mixed results when sharing a screen. My results have been deplorable with my keystrokes just not working or doing strange things entirely. I've had much better success with VSCode (I am truly sorry to say) but VSCode with Kotlin is still very early days especially for quickly spotting errors or suspect code. For that IntelliJ cannot be beat. But VSCode has Live Share which makes collaborating very easy and makes my keystroke issues gone. I even can use Emacs keybindings and still work flawlessly with others. So all this boils down to two questions: 1) has anyone figured out how to use Kotlin and VSCode that puts it on a par with IntelliJ for basic development (detect and show error/warnings and run tests); 2) has anyone figured out how to pair/mob remotely with Kotlin seamlessly?

Hi everyone! thanks for accepting me to the channel, i'm a beginner on kotlin, especially android programming. i hope i can learn a lot of things about android programming and we can work together in the future.