what do you think about

infix fun <T : Any?> T.`if`(condition: Boolean): Pair<Boolean, T> =
    Pair(condition, this)

infix fun <T> Pair<Boolean, T>.`else`(block: () -> T) =
    if (component1()) component2()
    else block()

Can someone explain such thing: in Java code there is an interface

Completer

that has only one method (function)

public abstract int complete(arg1, arg2, arg3)

, so when a variable

completer: Completer?

is assigned, it's done via Java lambda

completer = (arg1, arg2, arg3) -> { ... }

Instead of creating (at least) anonymous object of type

Completer

and

override

-ing the

complete

method. Is it possible to do something like that in Kotlin, or I have to do

object: Completer {
  override fun complete(arg1, arg2, arg3) { ... }
}

Why I can't do it with lambda -- because the compiler complains that

completer

must be of type

Completer?

, not

(???, ???, ???) -> Unit

With 1.3 stable release, context switching using lambda expression is still marked as experimental. Would it be 'ok' to use inside a production app?

I'm trying to test if I successfully moved my project to JPMS by running manually

jdeps

, however I need to specify where to find the

kotlin.stdlib

module, is there a standard location for that or shall I search in my

.m2

local gradle cache?

How to

MutableList<String>

->

Array<String>

?

I guess I'm getting into a deadlock, I have a multi-release dependency and then I set the multi-release option

manifest.attributes('Multi-Release': 'true')

, but now

jdeps

complains:

Error: kotlin-stdlib-1.3.41.jar is not a multi-release jar file but --multi-release option is set

Hi! Is it possible to define an extension function in java code? https://stackoverflow.com/questions/56987823/define-kotlin-extension-function-in-java-code

I have a class

class MyClass {
  companion object {
    public fun run(args: Array<String>) {
      ...
    }
  }
  public fun main(args: Array<String>) {
    ...
  }
}

How to call

run

from

main

?

if I compile kotlin code with coroutine to jar, can I run it with java?

internal inline fun <reified T: BaseResource> find( criteria: (query: IQuery<Bundle>) -> IQuery<Bundle>): T? {
        val forResource = client.search<Bundle>().forResource(T::class.java)

        val entities = criteria.invoke(forResource).execute()

        if ( entities.isEmpty ) {
            <http://log.info|log.info>("entity {} was not found", T::class.simpleName)
            return null
        }
        if ( entities.total > 1 ) {
            <http://log.info|log.info>("too many {} found", T::class.simpleName)
            return null
        }

        return entities.entryFirstRep.resource as? T
    }
    internal fun findLocation(name: String): Location? {
        return find {it.where(Location.NAME.matches().value(name)) }
    }

is there a method signature where I can just call

where

instead of

it.where

?

Is there a way to tell Kotlin to convert all instances of

java.lang.String

to

String?

rather than

String!

within a specified context, so that I get errors or warnings if I try to do (say)

resultset.getString(2).trim()

?

If I was to buy a new computer and I wanted the fastest possible compile times (specifically intelliJ/kotlin, though I do ofc have many other toolchains), what should be my focus point?

is there something like an

exists { Predicate } : Boolean

on collections?

does kotlin not have single

&

and

|

boolean operator?

also, do

&&

and

||

not have an

operator fun

?

In TypeScript there is a

Pick

type which lets you easily (and type-safe) define sub-shape:

interface Todo {
    title: string;
    description: string;
    completed: boolean;
}

type TodoPreview = Pick<Todo, 'title' | 'completed'>; // you can only specify properties of Todo here

const todo: TodoPreview = {
    title: 'Clean room',
    completed: false,
};

I'm trying to find out whether it's possible to achieve something like this in Kotlin

Is this a known bug?

is there anyway to have something like this

fun <T> wrapperFunc(block: (…) -> T): (…) -> T{
    println("wrapped")
    return block (…) -> T
}

and call it like

val testFunc = wrapperFunc {
    fun(a: String) -> println("a is $a")
}

testFunc("abc")

Any lightweight Kotlin interpreter in the market?

is

onEach

more efficient than

map

?

If I have a function

fun <T, R> Optional<T>.mapDefault(default: R, mapper: (T) -> R): R

and call it with a default of a subtype of a

sealed class

e.g.

maybeThing.mapDefault(Action.NoFoo) { thing -> Action.Foo }

then this fails type checking because

R

in

mapDefault

is bound to

Action.NoFoo

— is there a good way around this besides calling

maybeThing.mapDefault<Thing, Action>

?

is there a way to expose a

MutableMap

externally as a

Map

without using a "wrapper" member? i.e.

private val _data = mutableMapOf<Int, String>()
val data: Map<Int, String>
    get() = _data

is there a more compact way to express this?

init {
    require(level in 0..9) {
        "Valid range for parameter 'level' is 0 to 9"
    }
}

Hi all! do you know if there is a channel for kotlin multiplatform?

I have a doubt about

sealed classes

and method overloading. Imagine I have the following sealed class:

sealed class State {
    object A : State()
    data class B(val i: Int) : State()
}

And the following methods defined:

fun process(a: State.A): Unit {/**/}
fun process(b: State.B): Unit {/**/}

I should be able to call

process(state)

with an instance of

State

since the compiler knows that there are only two subtypes of it and that the method is defined for both of them. But it forces me to check the type (with a

when

for example):

fun newState(state: State) = process(state) //doesn`t compile (None of the following functions can be called with the arguments supplied)
fun newState(state: State) = when(state) { // this works but its really verbose 
    is State.A -> process(state)
    is State.B -> process(state)
}

Is there any special KDoc tag for generics?

How can I make IntelliJ not complain about this for the entire project?

I think Kotlin is great for backend servers. We have been debating in our company to fully switch over to Kotlin; the only reason we are having trouble convincing orthodox Java folks is because they argue they have not seen Kotlin on backend and it's only designed for front-end codebase. It would be nice if Kotlin's website can showcase Backend server usecases. Because everything points to Androind usage right now

how I can store the instances into a global list when the classes instantiate? in python it’s like alist = [] class T: def __init__(self): alist.append(self) then I can get all the instances of class T in alist