kotlinlang #announcements

inline fun <reified T> ObjectMapper.read(json: String) = readValue<T>(json)
inline fun <reified T> ObjectMapper.readList(json: String) = read<List<T>>(json)

val mapper = ObjectMapper().registerKotlinModule() // fasterxml.jackson
data class Person(val name: String, val role: String)
val json = """[{"name":"Alice","role":"transmitter"},{"name":"Bob","role":"receiver"}]"""

val value1 = mapper.read<List<Person>>(json)
val value2 = mapper.readList<Person>(json)
println(value1) // value1 is a List<Person>
println(value2) // value2 is a List<Map<String, Any>>

When composing a reified type through multiple inline functions, the generic part seems to get gobbled up by the erasure, like it wasn't reified...

2 replies · 2 participants

Philipp Mayer

06/18/2020, 10:24 AM

Is there a more idiomatic way to do the following operation? Thank you!

it.receiver

can either be of type ABC or DEF. If its ABC, collect to the first list, if its DEF, collect to the second list

val payments = findOpenPayments.get()
                .groupBy { it.receiver == "ABC" }

        val somePayments = payments.filter { it.key }.flatMap { it.value }
        val otherPayments = payments.filter { !it.key }.flatMap { it.value }

5 replies · 3 participants

Pacane

06/18/2020, 1:39 PM

Is there a way to filter a list with a predicate, but return 2 lists, one containing the matches, and another containing the non-matching elements?

2 replies · 2 participants

Jakub

06/18/2020, 1:47 PM

Is there an elegant way to add something to map only if it’s not null? code below won’t compile

mapOf(
  LIST_ID to listId,
  eventId?.let { EVENT_ID to eventId }
)

3 replies · 3 participants

dave08

06/18/2020, 3:49 PM

Is there a way to do this:

val fixture = listOf(
    mapOf(
        "a" to listOf(1,2,3),
        "b" to listOf(4)
    ),
    mapOf(
        "a" to listOf(5,6,7),
        "c" to listOf(8)
    )
)

// Should become
val result = mapOf(
  "a" to listOf(1,2,3,5,6,7),
  "b" to listOf(4),
  "c" to listOf(8)
)

3 replies · 3 participants

turansky

06/18/2020, 8:48 PM

Is there way to mark method/property as ignored by IDEA autocomplete?

// must be invisible in autocomplete
fun first() {}

fun second() {}

6 replies · 3 participants

Pierre Marais

06/19/2020, 10:40 AM

Is there a function in Kotlin similar to scala's

.group

on a collection? i.e.

val list = List(1,2,3,4,5,6,7,8,9,10)
val grouped = list.group(2)
// List(List(1,2), List(3,4), List(5,6), List(7,8) , List(9,10))

3 replies · 2 participants

Slackbot

06/19/2020, 11:03 AM

This message was deleted.

3 replies · 3 participants

Paul Stott

06/19/2020, 12:11 PM

Silly question, but does anyone know how you set a property of java.lang.Class in yaml, specifically the micronaut.executors.*.thread-factory-class property? I've tried variations of the theme

my.FixedThreadFactory::class.java

2 replies · 2 participants

Kelvin Law

06/19/2020, 12:52 PM

Hi, in Java, it is considered bad practice for try catching

Throwable

instead of `Exception`Does anyone know why

runCatching

for

kotlin.Result

is catching

Throwable

instead of

Exception

? https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/run-catching.html

3 replies · 2 participants

Va3000

06/19/2020, 1:55 PM

hello friends i am new here. I am searching channel ODS but i can not find it. is here some channel for people who interested in Ods.ai

6 replies · 2 participants

Rita Curado

06/19/2020, 1:58 PM

Hi! I am trying to add a processor annotation inside a

build.gradle.kts

file but it keeps saying that I have mismatch types:

Type mismatch: inferred type is String but Action<KaptExtension> was expected

plugins {
    id( "com.android.library")
    id("dev.icerock.mobile.multiplatform-resources")
    kotlin("multiplatform")
    kotlin("kapt")
}

kotlin {
  sourceSets {
     val androidMain by getting {
            dependencies {
                implementation("com.github.bumptech.glide:glide:4.11.0")
                kapt("com.github.bumptech.glide:compiler:4.11.0")
            }
        }
  }
}

Does anybody know how to use

kapt

2 replies · 2 participants

Robert Jaros

06/19/2020, 4:04 PM

how to translate this from groovy to kotlin gradle dsl?

dependencies {
    compile fileTree(dir: 'lib', include: ['*.jar'])
}

2 replies · 3 participants

Guy Bieber

06/19/2020, 7:59 PM

java.security.cert.CertificateException: com.android.org.conscrypt.OpenSSLX509CertificateFactory$ParsingException: com.android.org.conscrypt.OpenSSLX509CertificateFactory$ParsingException: java.lang.RuntimeException: error:0c0000be:ASN.1 encoding routines:OPENSSL_internal:WRONG_TAG
	at com.android.org.conscrypt.OpenSSLX509CertificateFactory.engineGenerateCertificate(OpenSSLX509CertificateFactory.java:284)
	at java.security.cert.CertificateFactory.generateCertificate(CertificateFactory.java:366)
	at com.nikolamotor.crypto.crypto.PublicKeyToX509Cert(Crypto.kt:316)
	at com.nikolamotor.crypto.crypto.storeKeyPair(Crypto.kt:374)
	at com.nikolamotor.crypto.crypto.generateKeyPair(Crypto.kt:433)
	at com.nikolamotor.crypto.crypto.generateTestKeyPair(Crypto.kt:287)
	at com.nikolamotor.crypto.CryptoTest.<init>(CryptoTest.kt:47)
	at java.lang.reflect.Constructor.newInstance0(Native Method)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
	at org.junit.runners.BlockJUnit4ClassRunner.createTest(BlockJUnit4ClassRunner.java:217)
	at org.junit.runners.BlockJUnit4ClassRunner$1.runReflectiveCall(BlockJUnit4ClassRunner.java:266)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:263)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at androidx.test.ext.junit.runners.AndroidJUnit4.run(AndroidJUnit4.java:104)
	at org.junit.runners.Suite.runChild(Suite.java:128)
	at org.junit.runners.Suite.runChild(Suite.java:27)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
	at androidx.test.internal.runner.TestExecutor.execute(TestExecutor.java:56)
	at androidx.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:392)
	at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:2196)
Caused by: com.android.org.conscrypt.OpenSSLX509CertificateFactory$ParsingException: com.android.org.conscrypt.OpenSSLX509CertificateFactory$ParsingException: java.lang.RuntimeException: error:0c0000be:ASN.1 encoding routines:OPENSSL_internal:WRONG_TAG
	at com.android.org.conscrypt.OpenSSLX509CertificateFactory$Parser.generateItem(OpenSSLX509CertificateFactory.java:122)
	at com.android.org.conscrypt.OpenSSLX509CertificateFactory.engineGenerateCertificate(OpenSSLX509CertificateFactory.java:282)
	... 34 more
Caused by: com.android.org.conscrypt.OpenSSLX509CertificateFactory$ParsingException: java.lang.RuntimeException: error:0c0000be:ASN.1 encoding routines:OPENSSL_internal:WRONG_TAG
	at com.android.org.conscrypt.OpenSSLX509Certificate.fromX509PemInputStream(OpenSSLX509Certificate.java:161)
	at com.android.org.conscrypt.OpenSSLX509CertificateFactory$1.fromX509PemInputStream(OpenSSLX509CertificateFactory.java:227)
	at com.android.org.conscrypt.OpenSSLX509CertificateFactory$1.fromX509PemInputStream(OpenSSLX509CertificateFactory.java:223)
	at com.android.org.conscrypt.OpenSSLX509CertificateFactory$Parser.generateItem(OpenSSLX509CertificateFactory.java:101)
	... 35 more
Caused by: java.lang.RuntimeException: error:0c0000be:ASN.1 encoding routines:OPENSSL_internal:WRONG_TAG
	at com.android.org.conscrypt.NativeCrypto.PEM_read_bio_X509(Native Method)
	at com.android.org.conscrypt.OpenSSLX509Certificate.fromX509PemInputStream(OpenSSLX509Certificate.java:155)
	... 38 more

1 reply · 2 participants

Guy Bieber

06/19/2020, 7:59 PM

I have an EC keypair generated with the AndroidOpenSSL provider. I am having an issue trying to store (and eventually retrieve) the key to the Android Keystore. Here is what I try.

val certArray : Array<Certificate> = arrayOf(PublicKeyToX509Cert(keyPair.public))
keyStore.setKeyEntry(alias, keyPair.private.encoded,  certArray)

private fun PublicKeyToX509Cert(pubKey: PublicKey): Certificate{
        var pem = ecPublicKeyToCert(pubKey as ECPublicKey)
        Log.v(TAG,"PEM:\n${pem}")
        val targetStream: InputStream = pem.byteInputStream()
        return CertificateFactory.getInstance("X.509").generateCertificate(targetStream)
}

I get the following error trying to store the key:

6 replies · 3 participants

groostav

06/19/2020, 9:17 PM

hey guys, my software takes math expressions from users and evaluates them (eg

x1 + x2 - max(thirdVar, fourthVar) * cos(y6)

). Thus I got to write a little compiler and I did it on top of antlr. I recently converted it to generate a little stack assembly language (implemented with a sealed class, eg (

sealed class ASM()

data class PushI(val int: Int): ASM()

object Multiply: ASM()

data class InvokeBinary(val name: String)

), expecting that to be fast as hell. its not. Its actually slower than when I just did a tree evaluation. I'm going to stripe the sealed classes such that they use enums, in hopes that makes things run faster. I want to be able to evaluate these expressions at the rate of ~100,000 per sec. Any idea how i might get there? this is https://github.com/EmpowerOperations/babel\

3 replies · 2 participants

Simon Lin

06/20/2020, 8:31 AM

Can we only allow the latest consumer receive data when use

flow

? For example,

val flow = flow { 
    var i = 0
    while(true) { 
        delay(1000) 
        println("Emit $i")
        emit(i++)
    }
}

launch { flow.collect { println("A: got $it") } }
launch { flow.collect { println("B: got $it") } }

I want only B can get data and if B stop collect than A can get data.

5 replies · 2 participants

Nikky

06/20/2020, 10:19 AM

since in #kotlinx-html are just a dozen of people, i hope here anybody knows this stuff

3 replies · 2 participants

Toddobryan

06/21/2020, 6:58 PM

And to confuse things even more, when I add the same version of the project itself to my Gradle build instead of depending on the jar, everything builds fine.

3 replies · 2 participants

Slackbot

06/22/2020, 2:44 AM

This message was deleted.

1 reply · 2 participants

LoganDark

06/22/2020, 7:17 AM

Does anyone know what's going on here?

83 replies · 4 participants

Animesh Sahu

06/22/2020, 11:54 AM

Somebody uses Kotlin Scripts? It seems a simple hello world program takes 3800ms compared to python taking around 60ms. Is it supposed to be that slow or?

1 reply · 2 participants

LoganDark

06/22/2020, 12:03 PM

I don't think Kotlin is interpreted, doesn't it need to be compiled to a Java program before running? And then that incurs JVM startup costs and all that...

6 replies · 3 participants

kenkyee

06/22/2020, 12:22 PM

First run is slow because it gets compiled...

4 replies · 3 participants

Slackbot

06/22/2020, 1:38 PM

This message was deleted.

1 reply · 2 participants

darkmoon_uk

06/23/2020, 3:41 AM

Itching to know when 1.4 is going to be released - @Dominaezzz what's the latest from your crystal ball?

👆 1

5 replies · 6 participants

Animesh Sahu

06/23/2020, 10:33 AM

Did sb read it? https://kotlinlang.slack.com/archives/C0922A726/p1592805872467900

1 reply · 2 participants

Xuc Xiem

06/23/2020, 11:21 AM

Hi All, I have a

Iterable<A>

and want to create a

Map<A, Int>

with a function

f: A -> Int?

. The values in the map cannot be null. So I write something like this:

iterable
  .map { Pair(it, f(it)) }      // Iterable<Pair<A, Int?>>
  .filter { it.second != null } // still Iterable<Pair<A, Int?>> but we can be sure the Int is not null
  .map { Pair(it.first, it.second!!) } // now it is Iterable<Pair<A, Int>>
  .toMap()

Is there any better way?

9 replies · 4 participants

Title

Xuc Xiem

06/23/2020, 11:21 AM

Hi All, I have a

Iterable<A>

and want to create a

Map<A, Int>

with a function

f: A -> Int?

. The values in the map cannot be null. So I write something like this:

iterable
  .map { Pair(it, f(it)) }      // Iterable<Pair<A, Int?>>
  .filter { it.second != null } // still Iterable<Pair<A, Int?>> but we can be sure the Int is not null
  .map { Pair(it.first, it.second!!) } // now it is Iterable<Pair<A, Int>>
  .toMap()

Is there any better way?

Chantry Cargill

06/23/2020, 11:23 AM

iterable.mapNotNull { thing ->
  f(thing)?.let { thing to it }
}

❤️ 1

➕ 4

👍 3

James Fagan

06/23/2020, 11:26 AM

iterable
  .associateWith { f(it) }
  .filterValues { it != null }

diesieben07

06/23/2020, 11:26 AM

James that still produces a

Map<A, Int?>

instead of

Map<A, Int>

James Fagan

06/23/2020, 11:29 AM

True, in this case I think its fine to then cast it to

Map<A, Int>

Or something like:

iterable
  .associateWith { f(it) }
  .filterValues { it != null }
  .mapValues { it ?: 0 }

diesieben07

06/23/2020, 11:29 AM

Unchecked casts should be avoided if you can...

James Fagan

06/23/2020, 11:31 AM

IMO the cast is fine when it's guaranteed to be safe 🤷‍♂️

Xuc Xiem

06/23/2020, 11:54 AM

The cast is fine, however IntelliJ will give a warning, right? Then I don't know which warnings are good, which are bad. The

iterable.mapNotNull { thing -> f(thing)?.let { thing to it } }

is excellent. I always wonder what's the equivalent of Scala's

.collect

in Kotlin.

mapNotNull ?.let

might not be that powerful but good enough.

diesieben07

06/23/2020, 11:55 AM

I think

mapNotNull

is the closest equivalent

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