kotlinlang #announcements

I'm having an issue with Kotlin generics and generic java classes. I'm trying to write a function for a DI lib that will takes two Class instances, one of interface and one of class implementing the interface (akin to Dagger's

@Binds

). So far, I can make it work with Kotlin types and even Java ones but it fails for generic Java types (like List<*> and ArrayList<*>). Is this limitation of generics system or am I doing something wrong? function:

fun <C : I, I: Any> bind(clazz: Class<C>, iface: Class<I>)

usage:

bind(ArrayList::class.java, List::class.java) //kotlin types, works fine
bind(java.util.ArrayList::class.java, java.util.List::class.java) // error: inferred type ArrayList<*> is not a subtype of List<*>

Felipe Álvarez

10/12/2019, 8:52 PM

Hey, I have a question related to data classes and Jackson deserialization. Let's suppose I have a

data class

as the class to be deserialized and I need to transform a JSON value into a custom object. For instance, a

String

value from JSON gets transformed into an

enum

value in my app, or color

String

into an

Int

. In Java, what I did was doing the transformation in the setter of the field. In Kotlin, it seems like Jackson uses the generated constructor for deserializing instead of getters and setters, so I end up having a

InvalidFormatException

because it cannot construct an instance of T type from some R type. BTW, I'm using

KotlinModule

in my

ObjectParser

Is there an elegant solution to this? Or this is not a good use case for data classes? A not so elegant solution I found was defining in my constructor a

var

of my "transformed" type and then a function

set<jsonFieldName>

that Jackson uses because it JSON field name and constructor field name don't match

groostav

10/12/2019, 9:46 PM

I've run into this kind of thing several times and it has often been the worst part of kotlin for me: the problem is when two types have the same short-name, eg:

kotlin.Pair

javafx.util.Pair

. Can these inspections be updated to detect error messages like "expected List<ASDF> but was List<ASDF>"... oh, expected == actual, => fully qualify them => "expected List<com.yourcompany.ASDF> but was List<somebody.else.ASDF>" Maybe this can should be my first PR against the kotlin plugin repo?

👍 1

pavi2410

10/12/2019, 10:55 PM

Why doesn't the vararg type checking work here? https://pl.kotl.in/opTRtUiQ7 (See

mix

variable)

LastExceed

10/13/2019, 7:39 AM

i have a function that takes 5 boolean parameters. i'd like to call it with all 10 possible value combinations where 3 of them are true and 2 are false. is there any fancy way to do this or do i just put 10 consecutive function calls ?

karelpeeters

10/13/2019, 6:34 PM

Is it possible to access the outer class instance for another instance of the current inner class? For example, I want to access

other@Outer.x

here but I can't figure out the syntax:

class Outer(val x: Int) {
    inner class Inner {
        fun foo(other: Inner): Int = this@Outer.x + other@Outer.x
    }
}

Paul Dhaliwal

10/13/2019, 9:06 PM

Is it possible to restrict creation of inner class objects to the outer class, so that other classes can’t do new innerObject = OuterClass.InnerClass()

Ifvwm

10/14/2019, 5:53 AM

sealed class Fix<F>
data class MkFix<F> (val x: F<Fix<F>>): Fix<F>()

this is possible?

Andreas Unterweger

10/14/2019, 11:18 AM

hello, i have a question related to pojos and how to create them in kotlin with data classes. we have a bean which gets successively filled with data in different methods. this bean has other beans nested. if i use val in data classes this seems to become an issue since i cannot reassign vals. on the other hand i want to avoid nullability. so i want to set a default value and later overwrite it. is there a pattern in kotlin for that?

bitkid

10/14/2019, 12:35 PM

is there a ready to use library for reading kdocs from my code?

jmfayard

10/14/2019, 4:53 PM

Here is a simple Kotlin question for which I don't have a simple answer Where should I put my extension functions?

Ashutosh Panda

10/14/2019, 5:13 PM

var nullTest:Int?=null
if(nullTest!=null)
    nullTest=1
else
    nullTest=0
println(nullTest)

Ashutosh Panda

10/14/2019, 5:16 PM

var nullTest:Int?=null
nullTest?println("1"):println("0")

standinga

10/14/2019, 8:42 PM

hey! what would be the best way to implement NaN with Long? I'm currently using Double.NaN to indicate invalid timestamps, but I'm leaning towards using milliseconds instead of seconds and using Long instead of Double. But I really like using NaN to indicate not set timestamp.

nkiesel

10/14/2019, 11:01 PM

Is there a way to force the compiler to call an object method before this object is passed as a parameter to another method or returned to the caller? The concrete use case is a Builder for which

applyBindings()

(a normal method of that builder) must be called before it's passed on. We currently do that manually, but this of course leads to bugs where this call was forgotten.

jojo.lichtenberger

10/15/2019, 7:32 AM

Hi all, maybe someone is eager to help to build a versioned data store (currently for XML and JSON in a binary format, whereas the storage engine has been written from scratch). SirixDB shares unchanged database pages between snapshots and even versions data pages... https://sirix.io the core has been written in Java but the REST-API is built with Vert.x and Kotlin (Coroutines) and I'd love to add Kotlin to other modules as it's so much more fun to write and read Kotlin code. I'd also love to provide a Kotlin DSL...

Prateek Grover

10/15/2019, 7:39 AM

which channel is dedicated for Q&A?

Maxim Kizub

10/15/2019, 7:49 AM

Hello everyone. I've created a feature request to add logical programming paradigm to Kotling. https://youtrack.jetbrains.com/issue/KT-34350?project=kt , can you comment on this proposal?

Slackbot

10/15/2019, 8:13 AM

This message was deleted.

thana

10/15/2019, 9:28 AM

when i have a property and method with the same name decalred on a class how can i get a reference to the property?

::propertyName

resolves to the method, not the property

Stephan Schroeder

10/15/2019, 11:01 AM

Does any body know when/if a video of the SpringOne Platform 2019 talk “The State of Kotlin Support in Spring” will come online? https://springoneplatform.io/2019/sessions/the-state-of-kotlin-support-in-spring

aballano

10/15/2019, 12:42 PM

Hi there, I'm trying to port some usages of AtomicInteger/Boolean/Reference to use github.com/Kotlin/kotlinx.atomicfu instead but apparently this is failing due to

factory kotlinx.atomicfu.AtomicFU::atomic is used outside of constructor or class initialisation

I'm just using them in local functions mainly, is this not permitted? if so, is there an alternative usage to do so? Thanks in advance! cc @elizarov

Stephan Schroeder

10/15/2019, 1:19 PM

What is the point of the immutable collections lib (https://github.com/Kotlin/kotlinx.collections.immutable) given the the Kotlin collections are already read only? Just to make sure that other devs can’t cast it back to MutableCollection??

Czar

10/15/2019, 2:19 PM

When implementing a Command and a Handler in Kotlin, e.g. in CQS or CQRS architecture, what's your preferred approach and why? 1️⃣

class DoSomethingCommand : Command

in DoSomethingCommand.kt and

class DoSomethingCommandHandler : CommandHandler<DoSomethingCommand, R>

in DoSomethingCommandHandler.kt 2️⃣ same as above but in one file, e.g. DoSomething.kt 3️⃣ Command handler is an inner class of the command:

class DoSomethingCommand : Command { class DoSomethingCommandHandler : CommandHandler<DoSomethingCommand, R> }

If that matters, command dispatcher is used, so handlers are only addressed directly in tests, otherwise it's

commandInstance.execute()

where

fun Command.execute() = /* get command dispatcher from static context and dispatch the command */

veesus mikel heir

10/15/2019, 4:33 PM

shorthand for calling a super version of an overriden function

trevjones

10/15/2019, 6:42 PM

you might give the android lint tool a look. they analyze the uast, not sure if they parse it manually or grab it from the compiler impl though.

👍 1

Mani

10/15/2019, 8:20 PM

Folks, I have a few queries on how to do this in Kotlin. 1. I have a bunch of urls as input. Need to iterate over them and download PDF's 2. Merge all these PDF's into one single PDF what are the relevant libraries for both downloading and merging? and is it advisable to do the merge on server? Worst case there can be 300, 400 urls at once. Also, since it is IO bound to download, will coroutines help in performance?

:stackoverflow: 2

taer

10/15/2019, 9:20 PM

Any best practices with inline classes and stringTemplates? I've making a pass through and ran into an interesting conversion gotcha. I have a String today, let's call it

version

I convert that into a wonderful inline class. I get all sorts of wonderful compile errors which I fix. However, this didn't pop up on the radar

val versionTag = "ver-$version"

As a String, this worked wonderfully. As an inline class, this ends up with the type name in the rendered String. I overrode

toString()

to handle this. I could have used the

val

from the inline class in the template as well. Either are valid solutions. I'm more worried about accidental usages in the future. Any thoughts as to making inline classes use in string templates a potential compile warning? Or something similar?

➕ 1

Robert Jaros

10/15/2019, 9:58 PM

A few months ago I've heard somewhere (kotlin forum? slack?) about a new tool for kotlin code generation (Kotlin Poet alternative). But I can't find the link. Anyone has an idea what project could it be?