kotlinlang #getting-started

This is a very difficult question to answer! Like most libraries the possibilities are almost limitless and any limitations may be irrelevant to you. The way I tend to work is just use something that helps me do whatever it is that I am trying to do... so if you can expand on your use case it would help figure out if it's a suitable technology....

Michał Kalinowski

12/30/2019, 3:28 PM

can I restrict somehow type of generics for example I would like implement `

class Angle<T>

where T can be Int or Float or Double and nothing else

kyleg

01/03/2020, 7:11 AM

@bjonnh I can’t tell the full context from what you posted (is this just the Boolean implementation? Or is the presence of

Boolean

in your code because the function must always deal with Boolean no matter which type of Term?) Assuming the pastebin contains the Output that only deals with Boolean, then why not

class Output<U: Term<V>, V>(val name: String) {
   private val callbacks: MutableList<suspend (U) -> V> = mutableListOf()
   // ...
}

and then have

class Term

class Term<V>

instead? I’m a relative neophyte with generics, though, so could be wrong. Plus I don’t have all your code, so maybe my suggestion doesn’t work anyway.

Will Nixon

01/03/2020, 2:49 PM

Hi all, is there any way to add a custom

Fling Listener

to a

RecyclerView

without creating a new RecyclerView class?

01/04/2020, 8:30 PM

hi ,i am a beginner in kotlin. I have been making android apps gor a long time , so should i start learning kotlin from scratch (like the way i learned java first) or should i focus on the Android part of kotlin?

bbaldino

01/06/2020, 5:23 PM

Is there any support for warning/erroring on an unused return value in kotlin? I found this thread https://discuss.kotlinlang.org/t/unused-result-warnings/602/5 but it's quite old, wondering if anything's changed since then. Everything I find when searching is related to unused arguments.

Imany

01/06/2020, 6:09 PM

What is main reason for having

with

and

apply

Ricjhill

01/10/2020, 1:20 PM

Is it recommended to mix Property-based Testing and Behavior Spec when using https://github.com/kotlintest

gabrielfv

01/10/2020, 8:37 PM

Hello, I have a result-pattern-like generic sealed class, I'd like to define objects that represent possible values that are independent of the type specified, is it possible?

sealed class State<out T : Any>
object Loading : State</* Type isn't relevant here */>()
data class Loaded<T : Any>(data: T) : State<T>()

There's no reason for

Loading

not to be an object in this context, neither is there any reason for it to specify a type. Changing the variance to contravariance and making it an

Any

is a design flaw in this scenario. Is there any convenient alternative to what I'm trying to accomplish here?

bbaldino

01/10/2020, 8:58 PM

Is the only way to get the KClass of a List type (say,

List<Int>

) to do

listOf<Int>().javaClass.kotlin

? I get complaints trying to do

List<Int>::class

oday

01/11/2020, 5:38 PM

how do I stick to keeping each class member immutable and still change the fields and modify them as I please?

oday

01/11/2020, 5:38 PM

every time I assign the object back to a copy of itself with the changed fields?

johnfn

01/11/2020, 11:44 PM

if (key in batches) {
        batches[key].add(entity)
      }

johnfn

01/11/2020, 11:50 PM

if (!batches.containsKey(key)) {
  batches[key] = emptyValue;
}

batches[key].add(entity);

Jérôme Gully

01/13/2020, 8:49 AM

if (message.fileDescriptor?.isImageType ?: false)

Is there a better way to write that ? because

fileDescriptor

can be null, i'm forced to write

?: false

, maybe kotlin as a sugar syntax to avoid the

?: false

like "if this is null, it's false"

oday

01/14/2020, 12:09 PM

hi, how can I refactor this with

indices

val n = arr.size
    for (i in 0 until n - 1) {
        for (j in 0 until n - i - 1) {

Mark

01/15/2020, 3:12 AM

Suppose I have a list of lambdas like:

List<(Int) -> Unit>

but I’d rather be more explicit so define an

interface MyFun: (Int) -> Unit

so that my list now looks like

List<MyFun>

. However, now, to create such a

MyFun

, I need to do something like

object: MyFun { override invoke(val: Int) { //some stuff } }

. Does this mean I’m creating an extra object compared to with not using the interface? If so, is there a better way?

Mark

01/16/2020, 2:45 AM

Destructuring: Suppose I have a function like this:

fun childVisible(left: Int, top: Int, right: Int, bottom: Int): Boolean

and I want to pass in the properties of an Android

Rect

. Is there a way to do the following more concisely?

val (childLeft, childTop, childRight, childBottom) = childRect
return childVisible(childLeft, childTop, childRight, childBottom)

Esa

01/16/2020, 11:47 AM

Hi, need a bit of help with where to start on refactoring my code. The code performs a list of tasks. The list itself is quite huge, so I’ve `.chunk()`’ed the list into smaller chunks. Each of these chunks I then start each task asynchronously, and await them all before continuing to the next chunk. I concider this a cheap hack by someone who doesn’t actually know how to implement parallellism fully.. If I instead want to convert this into a pool, that

amount of workers can pick tasks from, where do I start? Java has ThreadPool, what do we have when we use coroutines instead? The reason I want to convert it to a pool with fixed size of tasks to be run concurrently is because in my current

.awaitAll()

-implementation I rarely have all workers working simultaneously, but very often only half or less working because the other half is already completed, leading to a very inefficient implementation. The tasks themselves involve api-calls to the same destination, so some kind of throttling is very important. What I am looking for is someone to tell me what these concepts are called so I can do the googling more efficiently 🙂 Thanks in advance.

glade

01/16/2020, 7:13 PM

Hello All — Happy to be part of this community! We’re beginning to adopt Kotlin as our backend language and our intermediate language for datamodels/common configuration/constants. Maybe I can be redirected to the right channel. I’m trying to setup either a multiproject build or a composite build which allows me to transpile several of our datamodels into javascript and to the jvm. I’m currently blocked by the js project depending on a jvm project but disliking it. Finding documentation has been a tough because there’s so many outdated repositories and tutorials out there across gradle versions and kotlin versions. (The kotlin docs could use a version selector so we aren’t given so many caveats about crazy version matrices.) My current error is this

Could not determine the dependencies of task ':models-js:compileKotlinJs'.
> Could not resolve all task dependencies for configuration ':models-js:compileClasspath'.
   > Could not resolve project :models.
     Required by:
         project :models-js
      > Unable to find a matching variant of project :models:
          - Variant 'apiElements' capability com.gigwell.shared.models:models:1.0:

Can someone recommend a recently updated project (hopefully on 1.3.61+) and Gradle 5/6 that demonstrates this? The closest I found is kotlin-todomvc but its still using

"org.jetbrains.kotlin.frontend"

Cheers

glade

01/16/2020, 9:53 PM

This unable to find matching variant is the real error when models-js is trying to reference code from models. Models is jvm. If I change its type to js, the build completes. I need to use ‘models’ in both contexts.

Mark

01/19/2020, 2:23 PM

Is there a more concise way to specify this range

x..x+y

bum

01/20/2020, 6:14 PM

Hi, think its a stupid question but do we need to install

kotlin.test

from somewhere else? For what I understood the references says

kotlin.test

is a core library (https://kotlinlang.org/api/latest/kotlin.test/index.html) but when I try to use

@Test

annotation, Intellij tells me it is not defined What should I do to use kotlin.test library? Thanks in advance.

nfrankel

01/20/2020, 6:24 PM

kotlin.test
library provides annotations to mark test functions and a set of utility functions for performing assertions in tests, independently of the test framework being used.

emphasis on “library” it’s not part of kotlin per se so it should be used through your usual build tool cf. https://mvnrepository.com/artifact/org.jetbrains.kotlin/kotlin-test/1.3.61

👍 1

frogger

01/21/2020, 10:12 AM

what is the ideomatic way to get a copy of an Array without element

Wesley Acheson

01/21/2020, 3:01 PM

I don't know correct channel to post this question. I'll delete from getting started if it belongs only in spring. I'll delete from spring if it belongs only in getting started.

Nikola Milovic

01/21/2020, 3:31 PM

Trying to get into testing and start writing efficient and proper tests. Any links/ tutorials/ repos that can be helpful? Looking for good learning references.

MartinZaubitzer

01/21/2020, 10:59 PM

Hi, I try to generate documentation using Dokka. Worked out great, but there is no specific format for GitlabWiki docs. Can someone please explain a little more in depth how I can create my own format? I know about this: https://github.com/Kotlin/dokka/issues/279 But it is not really helping me. I am unsure where to start and what actual to do. Thanks.

Title

MartinZaubitzer

01/21/2020, 10:59 PM

Casey Brooks

01/21/2020, 11:05 PM

Custom formats for Dokka aren’t for the faint-of-heart, currently, but it can be done. I maintain a project that uses Dokka to create JSON-formatted output, and you’re welcome to browse the source and copy my setup for yourself, though it’s probably much more customized than you’d want it for Markdown output https://github.com/copper-leaf/kodiak

An alternative you might consider is using my other project, Orchid, to generate a full website, rather than just a wiki. It supports deploying to GitLab Pages, and renders nicer-looking Kotlin docs alongside your wiki docs. strikt.io is a good example of a project site documented with Orchid, and you can follow this tutorial to get started https://orchid.run/wiki/learn/tutorials/how-to-document-kotlin

MartinZaubitzer

01/21/2020, 11:27 PM

Ok thanks, I will try with Gitlab Pages. Does Orchid support Android? I have tried setting it up and got stuck with: "The java plugin has been applied, but it's not compatible with the android plugins"

Casey Brooks

01/22/2020, 12:00 AM

You’ll want to set the Orchid project up in a different subproject and point it to your Android modules

👍 1

View count: 2