kotlinlang #announcements

i think this extension function should be part of Kotlin fun <T> List<T>.exists(predicate: (T) -> Boolean): Boolean { return this.firstOrNull(predicate) != null } to do things like this someList.filterNot { p -> anotherList.exists { e -> e.anotherId == t.someId } }

gildor

11/02/2018, 9:22 AM

anywhere where I don’t have params or I have the same same set of params for all items and do not expect that this set will be changed Also if I want to iterate all available values of Enum

👍 1

ckchen

11/02/2018, 9:37 AM

“Each enum constant is an object.” I use this to decide if I need an Enum or sealed class.

👍 2

Fredrik Larsen

11/02/2018, 9:38 AM

Any news on multi catch in kotlin?

Barend

11/02/2018, 9:40 AM

Why does

GlobalScope.launch(Dispatchers.Main)

throw a

Fatal Exception: android.os.NetworkOnMainThreadException

and

GlobalScope.async

doesn't?

Nikky

11/02/2018, 9:58 AM

has anybody tried inine classes with enums yet ? seems to me that would fix

Each Enum constant is an object

Jakub

11/02/2018, 10:41 AM

Cool, how do you organize these functions @karelpeeters? Are they functions kept in data classes, extensions or they are separated Translators or something?

samir

11/02/2018, 11:07 AM

Should the second snippet not give a compiler error?

val imap = mapOf("a" to "a")
// val mmap = imap as MutableMap

    imap["b"] = "b" //compiler error

val imap = mapOf("a" to "a")
    val mmap = imap as MutableMap

    imap["b"] = "b" //runtime error java.lang.UnsupportedOperationException

orestisfou

11/02/2018, 12:01 PM

hello, is it possible to wrap on a sealed class classes of external libs?

yen

11/02/2018, 12:27 PM

What’s the best JVM memory profiler out there?

bod

11/02/2018, 1:53 PM

I've removed Kotlin dependencies from my project (so I transitively depend from the plugin sdk one) and I no longer have the issue . . . . .

spand

11/02/2018, 2:54 PM

In Gradle I can add java-library plugin and get access to the

api

method for the dependencies block. Is there a kotlin verion of this ? (do I need one ?)

Paul Woitaschek

11/02/2018, 3:44 PM

I am using kotlin for several years now and my programming style is evolving and becoming more functional. I write way more top level functions that I did one year ago. What I ask myself is: What do I do when my functions need more dependencies? Lets say I have a file with one public top level function and it calls private functions which themselfes call other functions too. When I now need the class X and Y in

fun d(x : X, y : Y)

it's painful to change all that code just for passing them through from

fun a(x : X, y : Y)

fun b(x : X, y : Y)

fun c(x : X, y : Y)

fun d(x : X, y : Y)

. Are there any common approaches / patterns to solve this?

Paul Woitaschek

11/02/2018, 3:56 PM

So a realistic example:

purchaseCardContents

calls

purchaseCardContents

which calls

toPurchaseCardContent

several times. Now I need a class

FormatSavings

in the last function

toPurchaseCardContent

. How do I get it there? When using a class for the whole logic, I just inject it through the constructor. The issue here is that

toPurchaseCardContent

doesn't know anything about

purchaseCardContents

so I would need to pass-through that class and everything else it needs. Maybe the better question is: How do I get / pass dependencies I don't want the caller to bother about in functional programming?

Untitled.kt

marcelo

11/02/2018, 4:29 PM

Clearly, I am new to

coroutines

. Don't know why this code

experienceTimer.tagVal("/sdsd/login").time {
  Thread.sleep(2)
}

unless I have

suspend {
  experienceTimer.tagVal("/sdsd/login").time {
    Thread.sleep(2)
  }
}

Don't think I am doing this right. I feel like the show Pimp My Ride,

Yo dawg, I heard you like
suspend
so I am adding a
suspend
and a block of
suspend
within the method that I want to
suspend
.

Timer.kt

nickheitz

11/03/2018, 9:28 AM

I'm hoping someone here can/will help, as my experience at discuss.kotlinlang.org had been one of unresponsiveness. I believe there is a bug in coroutines when combined with a class using @JvmSuppressWilcards. The description and example is here: https://discuss.kotlinlang.org/t/kotlin-1-3-and-coroutines/10084/4 This had only appears since Kotlin 1.3 and coroutines 1.0.0. should I just be raising this directly as a bug?

hudsonb

11/03/2018, 12:19 PM

In the following code, inspections warn about the redundant

->

in the

else

of the `when`:

internal fun hue(a: Double, b: Double): (Double) -> Double {
    val d = b - a
    return when {
        d.isTruthy() -> linear(a, if (d > 180 || d < -180) d - 360.0 * Math.round(d / 360.0) else d)
        else -> { _ -> if(a.isNaN()) b else a } // Redundant lambda arrow
    }
}

Removing it changes the type from

(Double) -> Double

Double

. Is there a better approach?

Hunter Breathat

11/03/2018, 4:15 PM

Hey so I'm having issues with setting up kotlin native via Intellij Ultimate

kingsley

11/03/2018, 4:35 PM

Following an earlier comment on this channel, using this Gradle Kotlin DSL to enable language flags seem to be working fine. However, there’s no documentation or a mention of it anywhere, regarding whether/not it’s a stable API that should/not be used. I’m curious if this is indeed a recommended solution

subprojects {
    afterEvaluate {
        the<KotlinProjectExtension>().sourceSets.all {
            languageSettings(closureOf<LanguageSettingsBuilder> {
                progressiveMode = true
                enableLanguageFeature("NewInference")
                enableLanguageFeature("InlineClasses")
                ...

                useExperimentalAnnotation("kotlin.ExperimentalUnsignedTypes")
            })
        }
    }
}

edwinRNDR

11/03/2018, 6:05 PM

I have recently been running into some (nitpicky?) problems with the typesafe builder pattern. It is the problem where functions inside the builder and outside the builder have similar names but different signatures (but it also happens for functions that have similar names) and users are easily tricked into the wrong function. I have been playing with shadowing those functions inside the builder to prevent users from using the wrong functions, but I can't say it is elegant: https://gist.github.com/edwinRNDR/18bacaf0fc51b44349c748eecbe76dde . What are nicer ways to deal with this problem?

Tolriq

11/03/2018, 7:03 PM

Got a quick question about using a Java API from Kotlin. The API in question is the Cast API from Google that is defined in a strange way.

public final class Cast {
public static final Cast.CastApi CastApi;

    private Cast() {
    }

    public interface CastApi {
   }
}

Accessing the static final field from Kotlin seems impossible AS always think I'm referring to the interface and not the field, is there any trick for that?

Benoit Duffez

11/03/2018, 9:15 PM

fun foo(bar: Long) { ... }
//elsewhere:
fun whatever(baz: Long?) = return when {
  baz ?: 0 > 0 -> foo(baz) // here
  else -> null
}

why is there no smart cast for baz being non null here?

APXEOLOG

11/03/2018, 10:04 PM

return behaviors
                .map { it to it.getFullUpdate() }
                .filter { it.second != null }
                .map { it.second.doSmth(it.first) } // Still nullable

getFullUpdate()

can return null, any way i can smart cast

it.second

to non-null?

karelpeeters

11/03/2018, 10:53 PM

.mapNotNull { it.second }.map{ it.doSmth(it.first) }

Hexa

11/04/2018, 11:08 AM

does anyone know why would this result to

undefine

when I'm expecting it should be either

true

false

obj shouldBe instanceOf(SomeClass::class)

Mahdi Javaheri

11/04/2018, 1:29 PM

can anyone explain this snippet to me? im confused what exactly happens

-.kt

Mahdi Javaheri

11/04/2018, 2:13 PM

can i use extension functions in polymorphic world? as i tested they are being resolved statically (at compile time)

open class AquariumPlant(val color: String)
class GreenLeafyPlant(size: Int): AquariumPlant("Green")

fun AquariumPlant.print() = println("AquariumPlant")
fun GreenLeafyPlant.print() = println("GreenLeafyPlant")

fun staticExample() {
    val plant = GreenLeafyPlant(size = 50)
    plant.print() // this print's GreenLeafyPlant

    val aquariumPlant: AquariumPlant = plant
    aquariumPlant.print() // this print's AquariumPlant !! but in polymorphism should be GreenLeafyPlant
}

is there a way to bypass this and benefit from Polymorphism

Nikky

11/04/2018, 2:16 PM

i do tis by making the class generic

Plant<PlantType>

Hexa

11/04/2018, 3:45 PM

does it make sense to mark a function/method as

internal

so that it can be unit tested? or is there a better way to do it without marking it as internal or public?

mzgreen

11/05/2018, 7:50 AM

What is a cleaner way to do this:

var foo: String = "foo" // set is not invoked during initialization
    set(value) {
        print("SET $value")
        field = value
    }

init {
    foo = "foo" // have to do this in order to invoke set function
}

property with custom setter can’t be

lateinit

Title

mzgreen

11/05/2018, 7:50 AM

What is a cleaner way to do this:

var foo: String = "foo" // set is not invoked during initialization
    set(value) {
        print("SET $value")
        field = value
    }

init {
    foo = "foo" // have to do this in order to invoke set function
}

property with custom setter can’t be

lateinit

Hamza

11/05/2018, 7:52 AM

var foo: String by Delegates.observable("foo") {
        prop, old, new ->
        println("$old -> $new")
    }
}

👍 3

u can also create your own delegation, as i dont think that runs on init

mzgreen

11/05/2018, 7:55 AM

Didn’t think about property delegates, thanks!

View count: 2