kotlinlang #announcements

I think I've found a compiler bug wrt inline classes, could someone confirm that my suspicion is correct? I'm trying to convert an existing units library that I use to use inline classes rather than boxing every entity. Once I'd completed, some of the tests for this project were failing with ClassCastException errors. I looked into it with a decompiler, and found that in one of the cases where I'd used the inline class, the decompiler shows a cast to Double from Length, and I assume that's what's causing the exception.

https://0x0.st/zj-H.png▾

The source version of that is this:

operator fun contains(p: Translation2d) = p.x in x..(x + w) && p.y in y..(y + h)

where all of the fields in use are Length, the inline class wrapping Double

Tuan Kiet

06/15/2019, 1:27 AM

e.g.

() -> Unit

Function0<Unit>

Jacques Smuts

06/15/2019, 9:00 AM

Is there a high quality version of the :coroutine: icon somewhere I can use? Google has not been much help thus far.

pindab0ter

06/15/2019, 4:17 PM

Are there conventions for where to put extension functions and properties? I have a lot of calculated properties and functions for classes I can’t change because they’re part of a framework and such, spread over multiple sub-packages. Currently I have one big “Utilities.kt” file where they are all bunched together, separated into categories with only comments. This is file is starting to feel too big and bloated, but I can’t immediately think of a decent alternative. I don’t like the idea of cluttering my packages with lots and lots of tiny files with just a few extensions in htem. How do others deal with this?

farzad

06/15/2019, 7:19 PM

https://stackoverflow.com/questions/56613415/a-pure-kotlin-way-of-implementing-publish-subscribe-pattern-which-is-type-aware

Sergio C.

06/16/2019, 12:14 PM

I'm trying to use the invoke function with objects that should be singletons, basically for having retrofit accept different base urls. If I call invoke("some url") in different places of the app how does that affect the singleton creation? Do I get the same object with the changed parameter , or is it creating a new object every time I call invoke?

Shawn

06/16/2019, 4:12 PM

val http200Status = object { val statusCode = 200; val description = "OK" }

println("The status code is ${http200Status.statusCode}")

👆 1

👍 1

Hullaballoonatic

06/16/2019, 5:15 PM

I don't suppose an abstract class has any way to define constructors or invoke operators of its inheritors?

Slackbot

06/16/2019, 8:44 PM

This message was deleted.

Slackbot

06/17/2019, 7:53 AM

This message was deleted.

pepe

06/17/2019, 11:49 AM

hey! I don't know if this makes much sense, but here it goes, imagine I have test utility method that among other things needs to check the type contained in an Either.Left, how would this be? is it even possible? is it just plain stupid trying to do so?

fun testStuff([...], type: ?????) {
  [...]
  assert((foo as Either.Left).a is type)
  [...]
}

Should

type

KClass

KType

?? I'm a bit lost

Yan Pujante

06/17/2019, 1:16 PM

does anybody know if the reference section on the kotlinlang website (https://kotlinlang.org/api/latest/jvm/stdlib/index.html) can be generated locally? Or another way to put it, is, is the code that generates these pages part of the kotlin project on github? Another project?

robstoll

06/17/2019, 1:40 PM

Is it possible to define a function which expects a type which has implemented

componentN()

=> https://kotlinlang.org/docs/reference/multi-declarations.html

🤔 1

rrader

06/17/2019, 3:00 PM

interface Some {
  fun calculate(str: String? = null)
}
class SomeImpl : Some {
  fun calculate(str: String? = null)
}

An overriding function is not allowed to specify default values for its parameters Why?

Toddobryan

06/17/2019, 3:30 PM

I'm trying my hand at writing an annotation processor and, ideally, would like access to the parameters and default values in a class's constructor. However, I'm not sure this is possible, since annotation processors use Java models for the elements they're operating on and Java doesn't have a concept of default values. Is this possible? Are there Kotlin models that annotation processors can use that know more than the Java ones?

Slackbot

06/17/2019, 4:30 PM

This message was deleted.

robstoll

06/17/2019, 4:47 PM

shouldn't

inline fun <reified T> foo() = T::class.qualifiedName

be disallowed if

inline fun <reified T> foo() = T::class

is?

streetsofboston

06/17/2019, 7:12 PM

I’m curious, Is there a difference between:

class Container<T>(val value: T)

and

class Container<T>(val value: T?)

? (note the extra

after the

Robert

06/17/2019, 7:43 PM

I get this error from Gradle when building:

Could not find org.jetbrains.kotlin:kotlin-stdlib-common:1.3.40-eap-107.

while I use

1.3.31-release-197

. There's no such version in one of my build files as for

1.3.40-eap-107

, there's no version specified. It says it is from a dependency, but I don't see it and I don't understand how it makes sense.

Required by:
    project :
    project : > project :KotlinBigInteger:bignum
    project : > project :KotlinBigInteger:bignum > org.jetbrains.kotlin:kotlin-test-common:1.3.31

Any clue? Even stranger, when I build the main project (composite build) it produces this error. When I build the dependency only, it seems to work fine 😕

Nezteb

06/17/2019, 8:15 PM

Anyone used any of these tools? https://github.com/google/error-prone https://github.com/typetools/checker-framework/ https://github.com/facebook/infer I’m looking to use them for some combined Java/Kotlin projects. The Kotlin code is pretty safe, but our Java code not so much 😕

sanmi

06/18/2019, 1:43 AM

Does anyone here know how to work with I/O(file) in Kotlin native. It appears I can't import java objects.

Ifvwm

06/18/2019, 4:08 AM

what's the difference between class and type?

:stackoverflow: 3

egek

06/18/2019, 2:50 PM

Enum.values.random()?

Rômero Ricardo

06/18/2019, 4:12 PM

Hi everyone, would you guys point me to the best source of information on Coroutines?

Ruckus

06/18/2019, 5:05 PM

Is it a known bug that this terminates at

UInt.MAX_VALUE

instead of

UByte.MAX_VALUE

fun main() {
    for (x in UByte.MIN_VALUE..UByte.MAX_VALUE) {
        println(x)
    }
}

ArtemHevorhian

06/18/2019, 7:06 PM

Thought about it too, but, from their website, "Kotlin/Native supports interoperability to use existing libraries directly from Kotlin/Native: C, Swift, and Objective-C frameworks", what I need instead is to use a C++ library, and I don't quite understand how to use Kotlin Native in this case, any suggestions?

zak.taccardi

06/18/2019, 7:53 PM

where are

typealias

stored in Kotlin metadata?

Andrew Gazelka

06/18/2019, 11:47 PM

is there a reason why multiple

fun main

functions are allowed in the same package but not multiple

fun main() = runBlocking { ... }

Andrew Gazelka

06/19/2019, 12:07 AM

https://kotlinlang.org/docs/reference/operator-overloading.html any reason

componentX()

functions are not on this page?

Ifvwm

06/19/2019, 1:52 AM

interface Source<out T> { fun nextT(): T }

Title

Ifvwm

06/19/2019, 1:52 AM

interface Source<out T> { fun nextT(): T }

Shawn

06/19/2019, 1:56 AM

have you read the docs on variance?

Ifvwm

06/19/2019, 2:25 AM

https://kotlinlang.org/docs/reference/generics.html

yeah

I don't understand why there're two concepts called " Consumers." and "Producers,"

it doesn't make sense to me

treatmaster

06/19/2019, 2:52 AM

as I understand, it is a solution in Kotlin to solve generics issue in Java although Java has its own solution

Ifvwm

06/19/2019, 5:36 AM

<? extends E> which means ? is a subclass of E

<? super E> which means ? is a superclass of E

this is simple, but the annotate <in E> and <out E> are not easy to understand

SiebelsTim

06/19/2019, 6:09 AM

I think it's easier. If E is coming out of the class (ie return types only), it can be an out type. If it's coming into the class (ie parameters) its an in type

Ifvwm

06/19/2019, 6:32 AM

but they're related with the type inheritance

now return or pass in

not

SiebelsTim

06/19/2019, 7:28 AM

They are related. I think you should read the section "Declaration-site variance" in the above link. The names in and out are chosen to reflect what I said above.

Mike

06/19/2019, 12:02 PM

It's more about simplifying the implications of defining a generic as

extends

super

. When writing in Java, unless you're very familiar with typing constraints, and what it means to allow variance of types, you REALLY have to think/read about when to use

extends

super

. Kotlin is trying to make it easier as one can easily determine if the generic is being used as an

in

or an

out

by reading the definition class, and can use the appropriate modifier. Make sense?

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