kotlinlang #language-proposals

) type before 1.3 release? I think it can be improved and you might want it to be improved for the future of language, I’m writing a KEEP but it takes a long time so I wanted to reach out so you know it’s coming

holgerbrandl

09/24/2018, 8:08 AM

Hi there, is there a ticket/KEPP about supporting local enums, that is enums which are defined in a function body? I think this would be pretty handy e.g. when writing api examples (like with dokka).

Fleshgrinder

09/24/2018, 5:33 PM

I would love to see these extension function in the core for Kotlin JVM. Not sure how to go about that. Should one create a KEEP for discussion, even if it something simple like this, or simply go ahead and create a PR?

Serializable.kt

adam-mcneilly

09/25/2018, 6:18 PM

I'm sure it's a pretty common request to have

when

statement support multiple conditions for the else block, does anyone know if there's an official feature request or discussion around this?

when (x) {
  1, 2 -> println ("one or two")
  3, else -> printlnt("doesn't compile")
}

➕ 2

voddan

09/26/2018, 5:00 AM

🔔 We have formed a new KEEP on class delegation and we are looking for feedback (and a sheppard)! @Dico is the author: https://github.com/Kotlin/KEEP/pull/154

👍🏻 1

😁 1

LeoColman

09/27/2018, 6:52 PM

Hey guys! Would it be valit for STDLib to contain an extension function such as

Int.length

, that counts how many numbers are in an Integer?

jkbbwr

10/05/2018, 11:50 PM

I wonder about

data class

is that basically designed as a compiler plugin? if so would there be a way to extend this in the future to add user defined (with compiler plugin)

Marc Knaup

10/08/2018, 2:32 PM

Is there any news on whether we'll get default arguments for generic parameters? 🙂 à la

class Something<Context = DefaultContext>

val something: Something

🤔 1

➕ 3

natpryce

10/10/2018, 7:50 AM

I’ve found an unusual edge case:

object foo {
    operator fun invoke() {
        println("an object")
    }
}

fun foo() {
    println("a function")
}


fun main(args: Array<String>) {
    foo() // prints "a function"
}

Ruckus

10/12/2018, 5:19 PM

Now that

main

can be suspended in 1.3, I propose an all-suspend plugin that would make all functions

suspend

functions (along the same lines of the all-open plugin), allowing a Go style of programming without having to mark each function as suspended. (Note: I know next to nothing about Go, so I could be way off in my comparison. I'm also not sure of the implications of this idea, so I haven't even decided if I like it myself, but I figured I'd throw it out there.)

👍🏼 1

👎 4

cbruegg

10/12/2018, 5:25 PM

I suppose this would not work well with Java-interop and stdlib functions that don't accept suspending functions as parameters.

elect

10/15/2018, 4:17 PM

I'd be very interested into some sort of solution to automatically infeer a field order for reflection

🤔 1

elect

10/24/2018, 8:18 AM

small feature requests, no more commas on multiline primary constructor parameters: https://youtrack.jetbrains.com/issue/KT-27785

👍 1

Vladyslav Sitalo

10/24/2018, 1:35 PM

is there somewhere a write up/discussion about the decision to make the

dynamic

type available only on the js platform? From what I’m reading for now it seems to be that it was not supposed to be like that initially (i.e. here: https://discuss.kotlinlang.org/t/dynamic-type/1145)

:trollface: 3

🚫 2

😱 1

👨‍💻 1

🙈 2

louiscad

10/25/2018, 10:17 AM

Hi, I think I actually found a use case for the

dynamic

behavior during prototyping/development: allow unresolved symbols after

TODO(…)

calls. I created an issue: https://youtrack.jetbrains.com/issue/KT-27818

👍 2

addamsson

10/26/2018, 11:56 AM

@orangy I'm not a language designer yet 😞

:thread-please: 1

natpryce

10/30/2018, 8:34 AM

I was wondering… is there a reason that Kotlin doesn’t support reified generic parameters on classes? I frequently find myself wanting it.

elect

10/30/2018, 1:01 PM

what about changing the

in order to allow calling function with inline classes from java? https://kotlinlang.org/docs/reference/inline-classes.html#mangling

karelpeeters

10/30/2018, 1:25 PM

Huh? They are mangled? Than what's the point of restricting inline classes to not have constructors? I thought the argument was that Java interop could always work around them.

karelpeeters

11/02/2018, 10:25 AM

for (i in 0 until 10 step 2) {
    println(i)
}

This code is only partially optimized, there is still an allocation of both an

IntRange

and an

IntProgression

. This get worse when this loop is part of another loop, that means two useless allocations per iteration of the outer loop. Are there plans to optimize all of that away?

Dominaezzz

11/02/2018, 11:44 AM

I have a vague idea, macro functions (and maybe classes). Where a function is marked with a keyword

macro

and like inline functions, will support "reified" generics and cannot be called outside of Kotlin (i.e Java), but instead of being inlined at the call site, they are generated and called. (Like templates in C++). Any reflection done in the function is inlined. This allows for IDE friendly templates(C++), easy code generation and maybe something similar to LINQ to SQL.

Dico

11/02/2018, 4:10 PM

@louiscad https://github.com/Kotlin/KEEP/issues/155 Try getting the keep a shepherd

louiscad

11/03/2018, 1:17 AM

You could be able to access this, but all the fields not defined as constructor parameters would be non accessible (marked as not initialized yet), unless it's from a lambda (like the one in

lazy { … }

)

addamsson

11/06/2018, 3:33 PM

What !? 😄

aarjav

11/12/2018, 9:38 PM

when to comment on an issue vs pull request in KEEP repo?

sksk

11/13/2018, 11:09 AM

Proposal: Generics new constraint

data class CPosition(var x: Int, var y: Int)

fun main(args: Array<String>)
{
    addComponent<CPosition>().apply {
        x = 5
        y = 5
    }
}


fun <T : new> addComponent(): T
{
    // create an instance of T
    val c = T()
    
    // do stuff with c
    
    return c
}

pablisco

11/20/2018, 11:48 AM

Just so I don't create duplicates, has there been discussions about having different type exposed by a getter? Example:

val items = mutableListOf<Item>()
  get() : List<Items>

zak.taccardi

11/24/2018, 8:40 PM

has there been a proposal to allow us to use a

typealias

as a namespace?

typealias MainViewModel = ViewModel<State>

Then I’d like to have classes defined as:

MainViewModel.State

➕ 2

marcusfs

11/28/2018, 3:10 PM

i don't know if this has been discussed in the past, but it'd be really nice if there was an enum-style shorthand for sealed data classes. basically so you can do something like this:

sealed data class Foo {
    First,
    Second(val x: Int),
    Third(val s: String)
}

instead of this:

sealed class Foo {
    object First : Foo()
    data class Second(val x: Int) : Foo()
    data class Third(val s: String) : Foo()
}

it's not a huge difference but it feels unnecessarily messy to do it the current way (especially when you mix in "no argument" data classes and have to use object/class instead) , and I imagine this is a pretty common use-case for sealed classes. what do you think?

👍 3

👎 6

Title

marcusfs

11/28/2018, 3:10 PM

i don't know if this has been discussed in the past, but it'd be really nice if there was an enum-style shorthand for sealed data classes. basically so you can do something like this:

sealed data class Foo {
    First,
    Second(val x: Int),
    Third(val s: String)
}

instead of this:

sealed class Foo {
    object First : Foo()
    data class Second(val x: Int) : Foo()
    data class Third(val s: String) : Foo()
}

👍 3

👎 6

orangy

11/28/2018, 3:14 PM

It cannot be

enum

, all enum values are singletons.

marcusfs

11/28/2018, 3:20 PM

well yes it can't be a java enum, but it can be inner classes with a hidden constructor (so like sealed classes). or did you mean there is something conceptually in the language, or practical in the compiler that prevents the keyword from being used?

orangy

11/28/2018, 3:21 PM

enum is enum 🙂 it has

values

valueOf

, etc, that assumes all variants are singletons. Using same word for something that is significantly different is very confusing.

marcusfs

11/28/2018, 3:23 PM

fair enough 🙂 either way i think it'd be useful with a shorthand for algebraic data types like this

orangy

11/28/2018, 3:23 PM

enum

comes from the fact that all values are

enumerable

, after all.

marcusfs

11/28/2018, 3:24 PM

that's true - in this case you would only be able to enumerate the constructors

orangy

11/28/2018, 3:24 PM

so what’s wrong with sealed classes as they are?

having to write some

:Foo()

and

data class

marcusfs

11/28/2018, 3:25 PM

it's not that it's wrong, it just seems like a common use-case is unnecessarily messy

yes, and sometimes

object

if you don't have any arguments to a case

(or

class

i guess)

orangy

11/28/2018, 3:25 PM

It may be wordy, but I don’t think it’s messy. It states pretty explicitly what is what

marcusfs

11/28/2018, 3:29 PM

i guess it's a matter of taste to some extent, but especially that you have to jump between using object and data class makes the code align really poorly which doesn't help readability

and it can get quite noisy as well. here's a more practical example from an android app:

sealed class AddEditTaskEvent {
    data class DefinitionCompleted(val title: String, val description: String) : AddEditTaskEvent()
    object CreatedSuccessfully : AddEditTaskEvent()
    data class CreationFailed(val reason: String) : AddEditTaskEvent()
    object UpdatedSuccessfully : AddEditTaskEvent()
    data class UpdateFailed(val reason: String) : AddEditTaskEvent()
}

versus

enum data class AddEditTaskEvent {
    DefinitionCompleted(val title: String, val description: String),
    CreatedSuccessfully,
    CreationFailed(val reason: String),
    UpdatedSuccessfully,
    UpdateFailed(val reason: String)
}

orangy

11/28/2018, 3:38 PM

I agree with an idea that it could look better in specific cases. I don’t think

enum

is appropriate shortcut here.

As a side note you’d probably have a kdoc before each of the variants, no? 😉

marcusfs

11/28/2018, 3:39 PM

i'm not so attached to the name, it's really the shorthand i care about

it really depends tbh but i hear what you're saying 🙂 with functional patterns types can work quite well as documentation though, and documentation that type-checks has better longevity than comments 😉

karelpeeters

11/28/2018, 11:30 PM

(FYI: this exact concept is called

enum

in rust, which misses the JVM concept of enum entirely)

gildor

11/29/2018, 3:12 AM

One more problem with this approach, that now you have choice: use nested classes or don’t, for example your code snippet can looks as:

sealed class AddEditTaskEvent
data class DefinitionCompleted(val title: String, val description: String) : AddEditTaskEvent()
object CreatedSuccessfully : AddEditTaskEvent()
data class CreationFailed(val reason: String) : AddEditTaskEvent()
object UpdatedSuccessfully : AddEditTaskEvent()
data class UpdateFailed(val reason: String) : AddEditTaskEvent()

And used as:

CreationFailed("reason)

instead of

AddEditTaskEvent.CreationFailed

But with implicit sealed class you don’t have such choice.

marcusfs

11/29/2018, 9:17 AM

well, you can always import them explicitly - this isn't different from how enums work

gildor

11/29/2018, 9:20 AM

you can import explicitly, sure, but it’s all about naming. By default will be used full name, because sometimes it makes a lot of sense for naming. Like

Event.Success

SuccessEvent

, you don’t want to have

Event.SuccessEvent

, I just pointed that this proposal doesn’t work well with non-nested classes

marcusfs

11/29/2018, 9:20 AM

btw for the record swifts

enum

(or enum-with-associated-data as they refer to it) works like rust too. one really frustrating thing about their enum though is that the cases aren't subtypes of the enum type - in fact they are not even types at all and you can only access them using pattern matching.

@gildor ah, yes that's true. i don't think this would be useful for every use-case though, just the case where you are using sealed data classes as an algebraic data type. for example the equivalent in other languages would be: Swift

enum Foo {
    case First
    case Second(Int)
    case Third(String)
}

Rust

enum Foo {
    First,
    Second(int),
    Third(String)
}

Haskell

data Foo = First | Second Int | Third String

sealed data classes already have the right semantics for this, it's just that i think the syntax when declaring it is a bit verbose, as i stated above

gildor

11/29/2018, 9:35 AM

See, version of Haskell is exactly what I’m talking about. It’s

First

, not

Foo.First

. i don’t think this would be useful for every use-case

That’s the problem, you suggest new language feature and new syntax, which is big change itself, so should work for so many cases as it possible Maybe there are some other ways to avoid additional verbosity, but now it’s pretty limited, for example you also want to have constructor properties for parent sealed class, but this syntax doesn’t allow that

marcusfs

11/29/2018, 9:44 AM

honestly i would like this to be more of an extension/shorthand to existing language features rather than a completely new one. isn't there already precedent where language features work as shorthand for other features but don't support every possible scenario? i'm thinking of things like interface delegation being shorthand for implementing interfaces yourself (delegation is less verbose but also a strictly less powerful way to do it)

gildor

11/29/2018, 9:46 AM

class delegation is definitely a bad example of well designed feature and Kotlin team and Andrey Breslav many times mentioned this

marcusfs

11/29/2018, 9:47 AM

fair enough, it was just the first thing that came to mind

gildor

11/29/2018, 9:47 AM

but even in case of delegation it’s potentianlly removes much more boilerplate than this proposal (which is very limited)

marcusfs

11/29/2018, 9:48 AM

but do you think the idea of having a shorthand for this is a fundamentally flawed idea for kotlin, or is it more about my specific proposal?

gildor

11/29/2018, 9:49 AM

I would like to write less code for sealed classes, but I don’t have any good solutions which are flexible enough and play nicely with existing code.

and I think proposed solution is too limited to be a part of the language: enum keyword is misused, what about not nested classes, how to share properties

if use case is only for simplest cases (like Foo above), than I don’t see big advantages, it actually creates a new syntax for one particular use case of existing feature

marcusfs

11/29/2018, 9:57 AM

if it is a common use-case i don't see why it would be a bad idea to provide shorthand? just like

data class

is shorthand for a specific kind of

class

(namely a product type), i'd really like to see something like a

sealed data class

as a complement for supporting sum types.

gildor

11/29/2018, 10:00 AM

because data class saves a lot of typing

this one saves one constructor call without arguments

also has completely new semantics about classes, data classes and object

marcusfs

11/29/2018, 10:01 AM

plus mixed `object`/`data class` prefixes

gildor

11/29/2018, 10:01 AM

yes, and this is what I mean about new semantics, sorry bad word for this probably

what if you need just a class?

, i’d really like to see something like a
sealed data class

this actually interesting addition, maybe this makes more sense, because doesn’t clash with existing implementation

marcusfs

11/29/2018, 10:06 AM

that is the concept i'm trying to describe 🙂

gildor

11/29/2018, 10:06 AM

original proposal was about

enum

marcusfs

11/29/2018, 10:06 AM

it was in my original message but i updated the code now to also reflect it

sorry about that

orangy

11/29/2018, 10:08 AM

sealed data class

clashes with existing meaning. E.g. if you have

inner class

and you make it

inner data class

it doesn’t change syntax that radically

(again, I’m not against the idea itself, I just discard some syntactic ideas based on experience in this language design)

👍 2

marcusfs

11/29/2018, 10:09 AM

i really appreciate the feedback!

orangy

11/29/2018, 10:13 AM

Also note, that since each item is still a class, it can have a body (with functions, overrides, etc). So syntax should either accomodate for it (and make it non-ambiguous to parse), or disallow it in the short form.

marcusfs

11/29/2018, 10:13 AM

yes, that is true

even enums allow bodies after all

gildor

11/29/2018, 10:24 AM

even enums allow bodies after all

But the same body for each item, which may be too restrictive for sealed class (because each item has own types in constructor, so probably want to have own methods)

marcusfs

11/29/2018, 10:25 AM

yes, i agree

Dico

11/29/2018, 10:26 AM

So the thing he's proposing is enum-like syntax for a concept dubbed

sealed data class

. Body of the parent class can follow the

just like in enum class (even if I'm not personally a fan of that syntax)

The only thing that remains is how the parent constructor is called - in

enum class

you call the parent constructor instead of declaring a new one

Very interesting idea but it definitely needs to be approached critically. Come up with a design that has answers to points of critique.

marcusfs

11/29/2018, 10:35 AM

absolutely - this kind of feedback is precisely what i was looking for when bringing it up

louiscad

11/29/2018, 9:20 PM

Enum cases can have different classes as each case can have a body, so they're not so different from one level hierarchy nested sealed classes.

gildor

11/30/2018, 1:05 AM

Ah, yes, sure

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