Dear All, I want to build an instagram like stories feature. Any help / resources will be helpful. 🙏 TIA

I'm playing around with kotlin

contracts

and have run into a problem I need some expert help with. I'm trying to validate user input from a method that takes a couple of nullable parameters and would like to use

contracts

and the below

checkParamIsNotNullOrBlank

-function to avoid null checks at the end of my expression. Here's a simplified example of what I'm trying to achieve:

@ExperimentalContracts
    override fun validateInput(
        firstParam: String?,
        secondParam: String?,
        thirdParam: String?,
        listener: ValidationListener?) {
        var error: Boolean
        error = isParamNullOrBlank(firstParam) { view?.firstParamEmptyError() }
        if (secondParam.isNullOrBlank()) {
            view?.secondParamEmptyError()
            error = true
        }
        if (thirdParam.isNullOrBlank()) {
            view?.thirdParamEmptyError()
            error = true
        }
        if (error == false) {
            val validObject = Object.Builder()
                .withFirstParam(firstParam)
                .withSecondAndThirdParam("$secondParam^$thirdParam")
                .create

            listener?.onValidated(validObject)
        }
    }

Here's my "contracts"-method:

@ExperimentalContracts
fun isParamNullOrBlank(param: String?, onInvalid: (() -> Unit)? = null) : Boolean {
    contract {
        returns(false) implies (param != null)
    }
    val result = param.isNullOrBlank()
    onError?.invoke()
    return result
}

This doesn't compile because the compiler can't infer that

firstParam

is not null. Also every

if

expression should be evaluated as the view can display multiple errors.

I don't understand why kotlin is so different to others

Is 1.3.40 released ? Looking at https://github.com/JetBrains/kotlin it seems to be the case but I can't find any announcement ?

Using jdk proxies and Kotlin kinda sucks since all checked exceptions are wrapped in

UndeclaredThrowableException

. What are people doing instead ?

Is the new NPM integration also integrated with

ts2kt

?

I mean, I understand why this interaction works this way, but it still makes me sad ☹️ https://pl.kotl.in/_g7Nag0rP in my particular use case, it'd be nice if the

Bar1

was also added to

foos

, but I imagine in other cases, that would be horrendous

Using MVP - I have a call that returns for instance a number between 1-43, then I need to do something like if it's between 1 and 5 show this image, if it's between 6 and 29 another one, so since in Presenter I can't put anything about R and Android context, how do I let the view know which icon has to show? Because as far as I understand view doesn't have to do any logic. Or for instance, I get a Boolean from API and then from VIEW I want to show an image or another one, I thought about create showWhiteBackground() and showBlackBackground() and then call the correct one, this is ok if the value is between 2, but when it's between 1-43 I can not do something like this 😕

So am I right in thinking that sequences built via yielding are necessarily unbuffered, and that if I want some buffering I'll need to use channels?

is there a more clever way to accomplish this? maybe a way to generalize the behavior (delegation or annotation?), or does such a generalization already exist? https://pl.kotl.in/Z2joV2hL3

class MyClass(foo: Int, bar: Int) {
    private var fooLock = false
    var foo = foo
    	set(v) {
            fooLock = true
            
            if (!barLock) bar += (v - field)
            field = v
            
            fooLock = false
        }
    
    private var barLock = false
    var bar = bar
    	set(v) {
            barLock = true
            
            if (!fooLock) foo += (v - field)
            field = v
            
            barLock = false
        }
}

I'm a bit confused by "new inference is only enabled in IDE" statement. Doesn't new inference produce less compile errors? That would mean that IDE now warns about LESS errors before running compilation which could now still fail since compiler uses old inference. Or am I interpreting this statement wrongly?

In the latest 1.3.40 change log, I saw

String.encodeToByteArray

experimental API introduced there. And I have been using

String.toByteArray

since always. I want to know why there is such redundancy? What's the difference between them? (I don't think there is much or any difference at all)

"Starting from Kotlin 1.3-RC2, serialization plugin is shipped with the rest of Kotlin compiler distribution, and the IDEA plugin is bundled into the Kotlin plugin." — https://github.com/Kotlin/kotlinx.serialization

So if I'm not using Gradle I need to add the library explicitly?

hey anyone know how to specify the json key for a field on an object in serialization? i.e. seriesUUID in the app but the api sends as series_uuid? am i stuck with the object having series_uuid?

I had to change like half my code base for using typeOf

how I can create a type, that tpe contain String and Int?

Why isn't it possible to pass a charset to

ByteArray.decodeToString

with kotlin 1.3.40?

I'm seeing a weird new intention in 1.3.40, that I think has something to do with the new type inference. Is this a known bug?

what’s the preferred library to do POST GET stuff? RESTFul API

I updated to 1.3.40 and now intellij stopped to work (tons of

KotlinIdeaResolutionException: Kotlin resolution encountered a problem while analyzing KtNameReferenceExpression

) how can I downgrade the kotlin plugin?

Is it bad to put helper functions on a data class? For example say I have data classes that hold configuration/setting data for different kinds of actions. There can be lots of different types so it has a type field. Eventually I need to map it to the actual action class with business logic that uses the configuration/setting data. I could do a when(type) and instantiate respective action class and pass in the config data class. Or could I add something like: fun toActionClass(): SpecificActionClass = SpecificActionClass(this)

Is there a good way to declare that a function returns a nonnull type, where the generic used is nullable? For instance:

interface Call<T> {
    suspend fun call(): T
}

suspend fun <T> Call<T>.callNotNull(): T = call() ?: throw RuntimeException("Example")

val nonnullCall = object : Call<String> {
    override suspend fun call(): String = "notnull"
}

val nullCall = object : Call<String?> {
    override suspend fun call(): String? = null
}

suspend fun t() {
    val r: String = nonnullCall.callNotNull()
    val s: String = nullCall.callNotNull()
}

At its current state, I will get an error for

nullCall

since

s

is

String?

Type

T

may or may not be nullable, but the returning type is definitely not null. I can’t use contracts because this is a suspended function I can’t make the extension to

Call<T?>

or it won’t work for

nonnullCall

Do I have to make two extension functions for this to work? Is there something like

T!

that would indicate a type with nullability removed?

I think I found another issue with the new type inference:

fun fred(map: Map<String, Any?>) {
    ...
}

fun test() {
    fred(mapOf("a" to { x: Color -> x.grayValue() }, "b" to Color.BLUE))
}

The

{ x: Color -> x.grayValue()}

is marked as an error due to

Type mismatch

Required: Color

Found: (Color) -> UByte

But it compiles and runs fine

And another:

fun getResult(value: Any?) {
    val result = (value as? Map<*, *>)?.get("result")
    ....
}

The

get

call is marked as an error due to

Type inference failed. The value of the type parameter K should be mentioned in input types (argument types, receiver type or expected type). Try to specify it

But again it compiles and runs fine

I'm writing a simple app in vim + gradle:

class App {
  val listA = listOf(1, 8, 12, 17, 26, 31)
}

fun main(args: Array<String>) {
  val app = App()
  while (app.listA.hasNext()) {
    println(app.listA.next())
  }
}

But get this on

gradle run

Unresolved reference: hasNext
Unresolved reference: next

Have I forgot something? Something in Gradle?

Another obscure thing for me, why is this kind of mapping not possible?

fun main() {
    val a = listOf(listOf(32,53,23), listOf(13), listOf(34))
    val its = a.map(it.iterator())
    println(its)
}

map(it.iterator())

I have case where i need to find all duplicates in list by code and finally get values from duplicateList with lower dateTime. Any ideas?

fun main() {
      val fileList = listOf<FileName>()
}

data class FileName(val code: String, val uid: String, val dateTime: LocalDateTime)

Hi, is there a way to write anonymous suspend function? ``` val func = { // <- here I cannot call suspend functions } ``