kotlinlang #announcements

Hi folks, my name is Igbani Izuchukwu a software developer (web and mobile), am so happy to be here. Seeing vibrant devs like you all, is increasing my vibe for Kotlin. And it tells me that am not lost.

👋 23

krtko

05/11/2019, 8:17 PM

Makes me wish we had full value types support on the jvm

🙏 2

hhariri

05/12/2019, 6:35 AM

If folks want to discuss Jetpack compose, there's now a new channel for it, #compose with quite a few of the team members on there.

👍 7

karelpeeters

05/12/2019, 8:39 AM

~~fun <T> box(value: T) = value~~
actually no, that doesn't seem to work, it just immediately unboxes it at the callsite.

karelpeeters

05/12/2019, 8:45 AM

java.lang.Integer(6)

works.

👍 1

santiago

05/12/2019, 9:03 AM

I’ve been getting a bunch of errors when I compile that are difficult to understand. enum classes in Kotlin will get errors that say “invalid method declaration; return type required” and then point to the constructor of the enum. What I’m having trouble understanding is that the errors appear to be on a java file generated of the kotlin enum, or decompiled from it. I can’t quite figure out what’s going on here.

santiago

05/12/2019, 9:13 AM

Actually, this is exactly what I’m seeing, only I’m already using Java 8. 😞 https://stackoverflow.com/questions/53289265/invalid-method-declaration-in-kotlin-enum-class-building-with-gradle-wrapper

nikospamp

05/12/2019, 8:18 PM

Hello everyone! 🙂 I am trying to copy the data from some PDFs (n=150) which are created with a certain template in mind to an other pdf with different layout. I could copy-paste the info for all the 150 of them but I was wondering if any you have done something similar in kotlin or you know how I can achieve such a thing. Thanks a lot!

Pep Mendez

05/13/2019, 8:29 AM

Finally I got here, thanks

david-wg2

05/13/2019, 2:38 PM

does anyone have any experience with kotlin, intellij and bazel ?

Guru

05/14/2019, 5:58 AM

How can I destructure this Javascript code in kotlin?

Guru

05/14/2019, 5:59 AM

any idea? I need only a property of the specific object while de-structuring?

iex

05/14/2019, 11:38 PM

is there a more elegant way to initialize an object if a series of variables are non

null

, than:

Copy code

fun Foo.foo(): MyObj? {
    val var1 = var1 ?: return null
    val var2 = var2 ?: return null
    return MyObj (var1, var2)
}

iex

05/14/2019, 11:39 PM

oh I can put the

return null

directly in the initialization of

MyObj

🤔

iex

05/15/2019, 3:18 PM

got a null pointer because I'm accessing a (non null)

val

of another class in

init

🤔 I thought this would be impossible

nickk

05/15/2019, 4:10 PM

Is there a better way to write this? I need a reference to the object I am constructing, to be captured by the closure.

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class Action(val field1: String, val field2: String, var closure: () -> Unit = {} )  { }

val myAction = Action("value1", "value2")

myAction.closure = {            
    callAnotherFunction(myAction)
}

collection.add(myAction)

Is there a way to avoid defining the temp variable and do it all at once?

karelpeeters

05/15/2019, 4:26 PM

val closure

should probably be a function instead, used as in

myAction::closure

, but I'm trying to mimic your code as close as possible here.

Hullaballoonatic

05/16/2019, 5:06 AM

Is there a reason why one would want to limit the number of interfaces an object extends?

karelpeeters

05/16/2019, 5:08 AM

If you implement a lot of interfaces your object is probably a god object that does way too much.

➕ 5

iex

05/16/2019, 6:30 PM

variance problems:

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sealed class Result<out T, out E> {
    data class Ok<out T>(val value: T) : Result<T, Nothing>()
    data class Err<out E>(val error: E) : Result<Nothing, E>()

    fun <V> map(f: (T) -> V): Result<V, E> = when (this) {
        is Ok -> Ok(f(value))
        is Err -> this
    }

    fun <F> mapError(f: (E) -> F): Result<T, F> = when (this) {
        is Ok -> this
        is Err -> Err(f(error))
    }

    fun <V> flatMap(f: (T) -> Result<V, E>): Result<V, E> = when (this) { // <-- declared as "out" but it occurs in "in"
        is Ok -> f(value)
        is Err -> this
    }
}

iex

05/16/2019, 6:30 PM

if I remove the

out

from

I get other errors

iex

05/16/2019, 6:32 PM

ok was able to fix

iex

05/16/2019, 6:32 PM

Copy code

sealed class Result<out T, E> {
    data class Ok<out T, E>(val value: T) : Result<T, E>()
    data class Err<out T, E>(val error: E) : Result<T, E>()

    fun <V> map(f: (T) -> V): Result<V, E> = when (this) {
        is Ok -> Ok(f(value))
        is Err -> Err(error)
    }

    fun <F> mapError(f: (E) -> F): Result<T, F> = when (this) {
        is Ok -> Ok(value)
        is Err -> Err(f(error))
    }

    fun <V> flatMap(f: (T) -> Result<V, E>): Result<V, E> = when (this) {
        is Ok -> f(value)
        is Err -> Err(error)
    }
}

streetsofboston

05/16/2019, 6:46 PM

@iex Shouldn’t both <T> and <E> be out?, since the (sub)types only produces either a T or an E? Try this to make it work:

Copy code

sealed class Result<out T, out E> {
    data class Ok<out T>(val value: T) : Result<T, Nothing>()
    data class Err<out E>(val error: E) : Result<Nothing, E>()
}

fun <T,V,E> Result<T,E>.map(f: (T) -> V): Result<V, E> = when (this) {
    is Result.Ok -> Result.Ok(f(value))
    is Result.Err -> this
}

fun <T,E,F> Result<T,E>.mapError(f: (E) -> F): Result<T, F> = when (this) {
    is Result.Ok -> this
    is Result.Err -> Result.Err(f(error))
}

fun <T,V,E> Result<T,E>.flatMap(f: (T) -> Result<V, E>): Result<V, E> = when (this) {
    is Result.Ok -> f(value)
    is Result.Err -> this
}

Robert

05/16/2019, 7:56 PM

Any clue why Byte (https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-byte/index.html) does implement compareTo for datatypes like

Int

, but does not implement it on thru

equals

(except for Native)? At least, not thru

==

comparison operator

Florian

05/18/2019, 11:38 AM

what exactly is "KotlinJavaRuntime"

Florian

05/18/2019, 12:29 PM

is it the standard lib?

👌 2