kotlinlang #getting-started

Is there a fancy collections helper method that can help me do this sort of nested for loop when I need to consider each item in a list with the others?

for (firstIndex in (0..inputs.size - 2)) {
        for (secondIndex in (firstIndex + 1..inputs.size - 1)) {
            val firstInput = inputs[firstIndex]
            val secondInput = inputs[secondIndex]
            ...
        }
    }

gabin

12/02/2018, 12:26 PM

What is the difference between coroutine context and coroutine scope ?

febs

12/02/2018, 7:29 PM

I just discovered that you can explicitly use the word "constructor" when defining a class; and that is mandatory only when specifying a visibility modifier for the constructor, or when using an annotation. Hence, I am curious about what annotation one could use for a constructor and why. Many thanks.

Adam Hurwitz

12/04/2018, 5:03 AM

Hola Everyone, I'm looking for the best strategy to host a Kotlin app on AppEngine and have the main method run once deployed, similar to how a Jars main method runs. In the applications's main method is logic to retrieve content from an API request based on a Timer and save that information to a database. Jars take a long time to deploy to AppEngine (10 - 20 min) which slows down development and is why I would like to move away from this approach. I've deployed using Ktor, but the main method doesn't appear to be initialized without an endpoint being called. Any insight is appreciated! 🙂

CamilleBC

12/05/2018, 10:32 AM

... Sorry I should have posted in Android.

Nicolas Pittion-Rossillon

12/06/2018, 1:10 PM

Hey guys! I was wondering about a replacement for DataScience tools such as Pandas DataFrames in Python. Would anyone be able to suggest some reading materials, links or whatever about that? Even opinions are welcome! I’m used to DataFrames and i would love trying to improve what i do with Kotlin.

karelpeeters

12/07/2018, 12:49 AM

.asSequence()

👍 2

poohbar

12/07/2018, 2:15 AM

any easy way to increment a value of a key in map? even if the mapping does not exist yet?

Andreas Sinz

12/07/2018, 4:26 PM

@Steven McLaughlin what do you mean with obviously doesn't work?

febs

12/09/2018, 6:59 AM

Is it correct to say that the parameters in the default constuctors are not properties unless you don't define them as such? I. E. class Cippa ( a: Int, val b: String) b is a property but a is not. Also, when could it be useful to define parameters that are not properties? Hope the question's clear. Thanks everyone!

Slackbot

12/09/2018, 3:31 PM

This message was deleted.

febs

12/09/2018, 9:06 PM

...but why has that been removed? Looks useful to me.

Shan

12/09/2018, 9:09 PM

Hello all. I have a question I'm unsure how to google. Is it possible to have a function which takes as a parameter

anything that extends x

? For example I have a data class here (using tornadofx library, it provides the ViewModel class) which I would like for the lamda to take anything which extends a ViewModel.

data class CustomMenuItem (val name: String, val action: (E ? extends ViewModel) -> Unit)

febs

12/10/2018, 7:34 AM

I feel like this sentence from an article I'm reading is incorrect:

With Java, in-memory data “storage” comes in four shapes: variables, parameters, fields, and constants, in order of scope.

With Kotlin, parameters are similar with a few variations. They are final (so they cannot be assigned a new value), can have a default value (so we can omit > them when calling it) and their names matter (as we can use them when invoking).

Now, for the other three, things are more different. As in, they are all defined as properties.

I understood that properties are related to objects/classes (and they might have a backing field), but if I declare a val or var in a function then that is a variable Am I correct? Or wrong? Thank you 🙏

febs

12/10/2018, 8:19 AM

why the allByDefault declaration is marked as an error while the declaration of simple is not? This is the official documentation.

nestserau

12/10/2018, 10:25 AM

Is there a way to declare this Swift enum using sealed classes in Kotlin?

enum Optional<T> {
    case None
    case Some(T)
}

itnoles

12/10/2018, 9:10 PM

As for Electron, https://medium.com/@liran.tal/malicious-modules-what-you-need-to-know-when-installing-npm-packages-12b2f56d3685 very sad

Andreas Sinz

12/10/2018, 9:18 PM

@Robert you can try #tornadofx

Robert

12/10/2018, 9:24 PM

I have been trying to get the Java logger to work, but it keeps saying the reference to LoggerFactory is unresolved. Should I replace it with something else, or is it my project setup?

companion object { 
        private val log = LoggerFactory.getLogger(MyClass::class) // TODO

Robert

12/10/2018, 10:49 PM

One final question before I'm off to bed. My project doesn't seem to find any java related resources. For example when I try to import anything from the java namespace

java.etc

java turns red and is unresolved. I'm using gradle in IntelliJ IDEA CE. This is my multiplatform gradle file: https://gist.github.com/RdeWilde/eee5e77880971f77ee61518a5b447d7d Is there anything that i am missing?

dvlwj

12/11/2018, 3:30 AM

guys i just learning android mvp, but i need to have some

context

in the

presenter

, what i need to do? i need to make

http request

with the

data

shared preference

Robert

12/11/2018, 8:22 PM

I am looking for a tutorial or something on a workflow to modify external library that I use in my project. So fork it, change it, test it, pull request. Can I just change it somehow in my main project? Or do I have to clone it in a seperate project per library? (Using IntelliJ IDEA CE)

Olivier

12/12/2018, 8:59 AM

MVI ?

👍 2

dvlwj

12/13/2018, 2:23 AM

btw did anyone have a legit MVVM tutorial/page/article/whatever for newbie? i am trying it, but i think i am missing something, and well, i doesn't found one that is legit for newbie, most of them using RXthis RXthat, Dagger, etc which is i never use before. 😞

👍 1

oday

12/13/2018, 4:40 PM

this is how it turned out, but now I never get any results, although in the debugger the program is reaching the correct filter based on the correct toggle and knows when a toggle is active or not and oly checks against the appropriate predicate https://pastebin.com/mPuWzSGQ

oday

12/13/2018, 5:44 PM

the idea is there though @karelpeeters?

Mike

12/14/2018, 12:03 PM

And really, Java isn't oo in the way Alan Kay et al meant it to be. They meant oo more the way actors work. Objects that work independently and communicate via messages. And now I'm totally off topic...

blogscot

12/14/2018, 3:07 PM

Is there an nice way to generate a sequence like 0 1 2 3 2 1 0 …?

Giulio

12/15/2018, 5:50 PM

so this channel is really useless

poohbar

12/16/2018, 3:26 PM

ran into something a bit weird and was wondering if anyone could clear it up for me:

list.map {
  if (condition) {
    42
  }
  0 
}

I am used to not doing else branches in Java when not needed but it seems like here I get a list of zeros if I don't put the 0 into an else branch. 🤔 Has this bitten anyone before?

Title

poohbar

12/16/2018, 3:26 PM

ran into something a bit weird and was wondering if anyone could clear it up for me:

list.map {
  if (condition) {
    42
  }
  0 
}

I am used to not doing else branches in Java when not needed but it seems like here I get a list of zeros if I don't put the 0 into an else branch. 🤔 Has this bitten anyone before?

blogscot

12/16/2018, 3:35 PM

The last line within the map lambda is what you’re returning as the result. So your example will always result a list of zeros. `if`s in kotlin are expressions; in this example your throwing away the result.

Dominaezzz

12/16/2018, 3:36 PM

I struggled with this for days. Only the very last expression in the block is returned. So, with the else branch, the if expression is the last expression but without the else branch, 0 is the last expression.

poohbar

12/16/2018, 3:38 PM

i see.. thanks!

blogscot

12/16/2018, 3:38 PM

I tweaked your example @poohbar:

fun main() {
  val list = listOf(1,2,3,4,5)

  val result = list.map {
    if (it and 1 == 0) {
      42
    } else {
      0
    }
  }
  println(result)
}

Now it returns

[0, 42, 0, 42, 0]

poohbar

12/16/2018, 3:39 PM

yeah i figured it out, was just wondering about "why"

blogscot

12/16/2018, 3:43 PM

It’s a common practice in FP languages to use the last expression of a function as the return value. Saves typing, I guess

bjonnh

12/16/2018, 4:18 PM

almost any function has a return

so if you do:

if (condition) { log.somethingabout(it) } 0 log.somethingabout would return

which is not what you want here

Jukka Siivonen

12/16/2018, 7:00 PM

Yeah I was bitten by this, would be nice to get some warning at least. Also you can't put explicit return there so only way is to remember put else there

AngusMorton

12/17/2018, 1:09 AM

You can do a labelled return e.g.

return@map

(https://kotlinlang.org/docs/reference/returns.html#return-at-labels)

bjonnh

12/17/2018, 3:52 AM

Totally forgot about those. Thanks.

Hauke Radtki

12/17/2018, 9:12 AM

Watch the Kotlin Puzzlers from KotlinConf '17 & '18, helps a lot wrapping your head around the weirdnes that kotlin can offer 😉

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