kotlinlang #announcements

Nice to see that Kotlin gets a proper Path API (currently experimental). I guess I can soon reduce niok (https://github.com/robstoll/niok) to a few extra extension functions 👍

janvladimirmostert

01/08/2021, 3:53 PM

Out of curiosity, is this output always guaranteed across Kotlin JVM, Android, JS, Native, etc? I'm assuming Kotlin breaks up those ++i and i++ into separate lines?

var i = 0
val map = mutableMapOf<String, Int>()
(1..10).forEach {
   map["${++i}"] = ++i + i++
}
println(map)

{1=4, 4=10, 7=16, 10=22, 13=28, 16=34, 19=40, 22=46, 25=52, 28=58} To ask it differently, is the IR being generated always such that map[...] evaluates first, then the ++i and then the i++ ?

christophsturm

01/08/2021, 4:27 PM

is there a kotlin library that escapes strings to be safe as xml attributes? I could use https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/StringEscapeUtils.html but I would really like to avoid adding a dependency

dm6801

01/09/2021, 8:27 AM

Hello kotliners,

fun main() {
    fun fun1(name: String) = println("Hello $name")
    val fun2 = { name: String -> println("Hello $name") }
    function(::fun1)
    function(fun2)
}

fun function(callback: (name: String) -> Any) {
    //some complicated calculation
    callback("username")
}

Which one would you use, and why?

Chilli

01/09/2021, 12:44 PM

Is there any public API Kotlin annotation (like

[PublicAPI]

attribute in JetBrains Annotations .NET library) that would mark a class/method/… as public API and therefore stop showing warnings

Property could be private

CLOVIS

01/09/2021, 8:43 PM

Let's say I wanted to create a 3D game which requires access to some low level functions (for example Vulkan APIs), and I didn't like the C or C++ syntax. What are the options for Kotlin? • Fully using the JVM, with LibGDX or jMonkeyEngine. However, it's impossible to access low level functions directly. • Using an hybrid of JVM and C via JNI. However many benchmarks seem to suggest the speed aspects are not that great, because anything other than primitives must be copied back and forth to ensure thread safety. One solution could be to avoid arrays as much as possible and try to have as few native calls as possible, but it might not be doable as many calls might be required per frame • Fully native, however to my understanding Kotlin/Native is built for low RAM usage and not for fast speeds. The inability to ‘unfreeze' objects might be very good for IoT, but it doesn't sound that good for 3d game—please enlighten me if you have more insights for this. None of these solutions sound good, is there any I missed, or is it just not possible (at least currently)? I'm aware video games is probably not very high in Kotlin's roadmap, but I'm curious as to how it could compare to C# and other high level languages that are used.

andries.fc

01/10/2021, 4:24 AM

Does anyone know how construct KClass from Java? The reason I'm asking because I'm integrating a library into my app which uses a factory interface defined in Java, and I need to know from Java if class is in actual fact an Object instance?

paul Olukayode

01/10/2021, 5:42 PM

Is there any kotlin library that sopport xmpp

Safa Orhan

01/11/2021, 10:41 AM

Hello folks! I am an Android Developer / Trainer from Turkey. Currently I am working for my business on Kotlin / Android Dev training. Creating educational resources, shooting YouTube videos, writing blog posts and such. Nice to meet you all, let me know if we can collaborate on any thing (conference, workshop, live stream, etc.)

:kotlin-intensifies: 6

Animesh Sahu

01/12/2021, 4:10 AM

🤔 https://stackoverflow.com/q/65677685/11377112

scaventz

01/12/2021, 9:57 AM

Kotlinc

supports the option

-script

, but I can’t find detailed information about it. Where can I find the relevant documentation about kotlin script?

james

01/12/2021, 2:44 PM

Anyone know of any good resources for "why kotlin"?

mikehearn

01/12/2021, 4:28 PM

It hasn’t received any commits for three months.

:thread-please: 1

crummy

01/12/2021, 6:27 PM

I'd like to write Kotlin code server-side, with APIs that implement an interface, and auto-generate JS (or TS, even better) clients for my interfaces. The idea is, if I needed data from the backend, I'd add a method to the interface, regenerate the clients, and now it's available for use. I'm not 100% sure how to go about this though. One option I thought would be to use OpenAPI and maybe get Gradle to autogenerate clients. Is there a better way to do this?

muliyul

01/13/2021, 12:22 AM

Hey everyone this is not really related to Kotlin but I need help. I have an HTML I'd like to replace a portion of it (a json object) with my json. the markup looks like this

[html...] SwaggerUIBundle({ ... }) // the object I'm trying to replace is the parameter to this factory
[...html]

The object may have indentation, new lines etc. I came up with this:

html.replace("""\s*\{(\s*.*)*}\s*?""".toRegex(), myJsonFormattedString)

But since the expression resides between js brackets the regex is matching all the way to the closing bracket for example:

{ ... }) [...javascript] }

I tried to use the non-greedy modifier but it didn't seem to work. Your help is appreciated!

rajesh

01/13/2021, 9:03 AM

have two tables as following Post table and Comment table I need to create another table called Activity table which will store aggregate values of likes performed on post or comment. I want to use activity id column which must be EITHER post id or comment id. How do i do enforce this condition in database? (preferably hibernate)

Arief Hidayat

01/14/2021, 7:15 AM

#Ask any one know how to make this object inside array programmatically

Arthur Artikov

01/14/2021, 11:16 AM

Hi. What is the best way to get a delegate from a delegated property? I need it to wrap MutableStateFlow to a property delegate for my mini MVVM-framework. getDelegate requires kotlin.reflect package that is not optimal for Android development. I came up with this solution https://gist.github.com/aartikov/b64f462f50b5e5452c3df707db090a5f It uses a global (ThreadLocal to be more precise) holder to place a delegate there from getValue method. Do you have ideas how to implement it better?

Andrew Adams

01/15/2021, 12:01 AM

Hey guys I was curious is there was a super class that all classes that have a companion object inherit, and thusly can be extended? To enable the use of extension methods such as:

inline fun <reified T : Any> T.Companion.extensionMethod = ...

holgerbrandl

01/15/2021, 8:51 AM

How can I express else branches of for loops in kotlin? Python supports this (imho obscure feature) (see https://docs.python.org/3/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops), but I want/need to port some python code to kotlin. In python the

else

after a for loop it is executed when the loop terminates through exhaustion of the iterable but not when the loop is terminated by a
break
statement. Here is the yet non-functional example from the python docs ported to kotlin

for(n in (2..10)){
    for(x in (2.. n)){
        if(n.rem(x)==0){
            println("$n equals $x * ${n/x} ")
            break
        }
    }
    //todo else{ ???
    // loop fell through without finding a factor
    println("$ is a prime number")
}

natpryce

01/15/2021, 1:18 PM

When I use sealed classes, I end up writing lots of functions like:

fun doSomethingWith(arg : SealedBaseClass, otherArg: Int) = when(arg) {
    is SubclassA -> doSomethingWith(arg, otherArg)
    is SubclassB -> doSomethingWith(arg, otherArg)
 }

fun doSomethingWith(arg : SubclassA, otherArg: Int) = ... 
fun doSomethingWith(arg : SubclassB, otherArg: Int) = ...

What do people think of the idea of a sealed function, where the compiler generates the when boilerplate for you? E.g.

sealed fun doSomethingWith(arg : SealedBaseClass, otherArg: Int)

fun doSomethingWith(arg : SubclassA, otherArg: Int) = ... 
fun doSomethingWith(arg : SubclassB, otherArg: Int) = ...

I’m imagining the same rules would apply as for sealed classes: all implementations of the sealed function have to be in the same source file. And the compiler would check them for exhaustiveness.

➖ 2

❤️ 8

Nir

01/15/2021, 4:01 PM

If you want to write a DSL where the user can call some function to "break out" early from their own function, does this have to be implemented using exceptions internally? Is this considered bad? Here's a toy attempt at emulating python's else clause on for loops:

class BreakException : Exception("")

class Breaker {
    fun breakOut() { throw BreakException(); }
}

class ForEachElser(val runElse: Boolean)

fun <T> Iterable<T>.forEachElse(func: Breaker.(t: T) -> Unit): ForEachElser {
    val b = Breaker()
    return try {
        forEach{ b.func(it) }
        ForEachElser(true)
    }
    catch (b: BreakException) {
        ForEachElser(false)
    }
}

infix fun ForEachElser.elser(func: () -> Unit) { if(runElse) func() }

👀 1

Nir

01/15/2021, 4:32 PM

A separate DSL type question. One thing I've frequently encountered with DSL's that's a bit annoying is that infix functions generally cannot start a line. So if you are writing something that emulates an

else

or other control flow, as above, then I'd like to be able to write:

something {
    ...
}
my_else {
    ...
}

but this will never compile, you need to put the

my_else

after the brace. Does it seem reasonable at all that the compiler could consider allowing this to compile, specifically when you have an infix function starting a line like that

dMusicb

01/15/2021, 9:29 PM

Is there a way to monitor/assert there are no coroutines in a pending (maybe wrong word) state? i.e. I have a piece of code that dispatches some work in a coroutine on Dispatchers.IO and I'm having some trouble with it bleeding over between integration tests so I want to have a check that confirms all coroutines have completed

Ifvwm

01/16/2021, 6:32 AM

what String! mean? File(uri).length, it shows me none of the following functions can be called with arguments supplied public constructor File(uri: URI!)

📖 1

Oliver Eisenbarth

01/16/2021, 11:48 AM

Hi, I wanted to test improvements to inline classes in KT-1.4.30-M1. I thought it was possible to have inline classes with internal / private constructors? Is this not possible? If you want to have a look, here's some code.

Remy Benza

01/16/2021, 12:19 PM

Is there a way of serializing a

MutableList<Pair<Pair<String, Boolean>, Triple<String, String, Boolean>>>

type with the kotlinx serialization lib without writing a custom type converter?

serebit

01/16/2021, 6:15 PM

I created an issue for inserting a value for a constant at compile time, the one feature I miss from Go. Link: https://youtrack.jetbrains.com/issue/KT-44386

robstoll

01/16/2021, 9:08 PM

Is there any plan to support de-structuring nested classes which implement

component...

in the same line? So that something like the following would work:

val (a, (b, c)) = 1 to (2 to 3)

➕ 6

🔥 5

Zimri Leisher

01/17/2021, 2:37 AM

on a very simple program, gradle is getting stuck on every step and working very slowly: compiling kotlin, building, even running the main function. and when i call readLine(), the delay between me pressing enter andthe line being read is like 30 seconds

Title

Zimri Leisher

01/17/2021, 2:37 AM

the computer is otherwise fine, nothing else is occupying cpu

and memory is less than half used

the gradle classes task takes a minute even with no change to the code at all and 1 total class

i restarted computer, and changed the shared heap size to like 4 gbs

Alexey Belkov [JB]

01/18/2021, 11:33 AM

Do you use both Gradle and IDE Kotlin plugin 1.4.21? Do you compile from CLI or in IDEA?

Zimri Leisher

01/20/2021, 5:58 AM

I initially was compiling with gradle and ide kotlin plugin

but i tried with IDEA and it works fast

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