Hello, does anyone know why Kotlin kept the convention of

alllowercasepackagenames

from Java? What was the rationale? I'm about to name a package in camelCase because it's much more readable that way, but I'm wondering why I should follow that specific convention. EDIT: Same question for underscores (

_

) in package names.

I’m trying to figure out a more elegant way to write:

if (intent.getStringExtra(SUGGESTION_KEY) != null) {
    suggestionButton.text = intent.getStringExtra(SUGGESTION_KEY)
    suggestionButton.visibility = View.VISIBLE
} else {
    suggestionButton.visibility = View.INVISIBLE
}

I can’t write the following, because one arm returns a

String

and the other

Unit

:

intent.getStringExtra(SUGGESTION_KEY)?.let { suggestion ->
    suggestionButton.text = suggestion
    suggestionButton.visibility = View.VISIBLE
} ?: suggestionButton.visibility = View.INVISIBLE

(I know there is a function

intent.hasStringExtra()

, but I’d like a general solution not specific to intents.) How should I rewrite the original block of code, or is it best as is?

Any reason why one is marked as a function and the other one is a method?

Hi, i have some class like

class Foo<T> (val helper1: Helper1<T>, helper2: Helper2<T>)

. here i want

Helper1

and

Helper2

work on the same type

T

but in fact

Foo

doesn't really care about what

T

actually is - they just must match. Is there a way not having to declare the

T

on

Foo

itself? I don't want to write something like

Foo<*>

everywhere i'm using

Foo

Or maybe the better question: i sense there is some design flaw here but i cannot really put the finger on. What approaches are there, to resolve this flaw?

Hi all! I was under the impression that

KClass::sealedSubclasses

is not only part of the API of Kotlin 1.3, but also of it’s implementation, but apparently this needs

kotlin-reflect

. Now I’m on a constrained device and would rather not add a 2.7MB lib just for that. Are there alternatives (beside going back to a good old

enum class

)?

::main

in line 4 gives a an overload resolution ambiguity. I understand why it happens, but how do i resolve it? (i'd like to know the solution to both scenarios)

is there anything out of the box to convert code that can throw an exception to

Result

?

I'm trying to figure out an issue I have with dagger + kotlin. I have a class

@Module
class NetworkModule constructor(@Inject public var url: String)

but when I look at the decompiled code in java I see:

public final class NetworkModule {
   @Inject
   @NotNull
   private String url;

This is the error I'm trying to figure out "error: Dagger does not support injection into private fields private java.lang.String url;" Not necessarily a dagger issue, but somehow creating a private field in java even though I specify it to be public in kotlin?

how do you folks add constraints to your data classes? say if parameter a is null then b cant be not null

Which do you prefer? 1.

for (value in map.values) { … }

2.

for ((_, value) in map) { … }

Hi, I’m creating a kotlin library and I’d need to create a lot of functions. Is there a way to get (programatically) all keywords used in kotlin? I’ll need to escape then with backticks `. One example is the

continue

keyword that should become ``continue`` when I escape.

listOf("banana").map { it to 42 }.toMap()

is there an easier way to do this ? basically i want to turn a list into a map by providing a lambda that associates each element from the list with a value to form a key-value pair

Can I pattern match a

Pair<T, T>

(or tuple in general), whose elements are case classes? (I need to pattern match the subtypes of the sealed class)

Hi. Is it not kinda weird that a Set in Kotlin allows duplicates when mapping over the set? https://pl.kotl.in/r9b-MCq8p 😮

How can we create a 

!

 operator in Kotlin? For example, if I have MyClass defined as:

MyClass() {
  run() {
    println("finished")
  }
}

I’d like to create a situation where doing something like this:

val myObject = MyClass()
myObject!

is equivalent to

myObject().run()

the methods will be more complex since this is for a special library that I’m doing, but the simple idea is like this. How can we define this operator? I think it is possible because we have the 

!!

  one.

I'm looking for projects to contribute, does anyone know some?

Anybody know if there’s some way to do

TimeMark.elapsedSince(other: TimeMark)

? or plans to add it?

Hi Folks, I saw this article by Roman, https://medium.com/@elizarov/kotlin-and-exceptions-8062f589d07 I had been a Java developer and started adopting Kotlin few weeks back. Most of my code is very similar in terms of what I would write in Java 11. I am quoting Roman here

*As a rule of thumb, you should not be catching exceptions in general Kotlin code.* That's a code smell.

. I see that I can make changes to my APIs to validate and return rather than throwing and catching an exception. However, I failed to come up with a better code for one scenario. I have a Kafka consumer, which makes a call to a web API. so I have

onListen(p: Person) -> orchestrator(p: Persons) -> makeRestCall(p: Person) -> API

the exception flow here as I would do in Java is to handle all non response codes 200s. If there is an error returned from the API, I throw and exception, the orchestrator catches it. Is this an anti pattern in Kotlin? I think I am not the first person to have this issue, it would be of great help if someone can give a direction here. Thank you.

Hi, I have a pretty basic question: What are the practical uses/ advantages of Boolean functions like

and(), or(), not()

over Boolean operations like

&&, ||, !

. Thank you in advance for your answers.

is there a way to do this less copy-pasty that isn't completely over-engineered ?

Hey guys, I have a value object which holds a string:

data class SystemName(val value: String) {
    init {
        require(value == value.toLowerCase().capitalize()) { "Name $value must be capitalized!" }
    }

Right now, when I create the Object I always check if its lowercase with the first letter being capital. I'd like to let the object take care of

.toLowercase().capitalize()

, so I don't have to do it on my own. Searching google gives me mixed results which don't look that clean tbh. What would be your take on this? Thanks ahead! My current take is the following:

data class SystemName(val value: String) {
    init {
        require(value == value.toLowerCase().capitalize()) { "Name $value must be capitalized!" }
    }

    /**
     * automatically converts string to required format
     */
    companion object {
        fun createInstance(name: String) = SystemName(name.toLowerCase().capitalize())
    }

Hi! 🙂 I have a Matrix class with a primary constructor that takes two integer arguments (rows and columns) and a supplier function that tells it how to get its next element based on its indices:

class Matrix<N : Number>(private val rows: Int, private val columns: Int, f: (Int, Int) -> N) : List<List<N>>
by List(rows, { i -> List(columns) { j -> f.invoke(i, j) } }) {

Now I want to add a secondary constructor that would take an iterable (list or array) of elements, like this:

constructor(rows: Int, columns: Int, values: Iterable<N>) {
    val iterator = values.iterator()
    Matrix(rows, columns) { _, _ -> iterator.next() }
}

This doesn't work, says "call to primary constructor expected" Any advice on how to address this problem, Kotlin-style?

Hey guys! I am working on Spring Reactive using Kotlin. I am trying to find the best solution to get the

id

property value of generic

T

this is my code.

class BaseRepository(val client: DatabaseClient, val dataAccessStrategy: ReactiveDataAccessStrategy) {

    suspend inline fun <reified T> save(entity: T): T {

        val id = // How to get the id of entity?
        try {

            return client.insert()
                         .into(T::class.java)
                         .using(entity)
                         .map(dataAccessStrategy.converter.populateIdIfNecessary(entity))
                         .awaitOne()

        } catch (exception: Exception) {

            throw exception
        }
    }
}

What is the best approach to get the id of entity here?

im trying to figure out the best way to write some code for a library. in Elixir I used to be able to do something like:

def is_ten(x) when x > 10, do: "Greater than ten"
def is_ten(x) when x < 10, do: "Less than ten"

I need to write a kotlin function that always takes a string, but the logic is completely different based on that string, is there a way to encapsulate logic into a function that is called based on the parameter value similar to elixir guard clauses?

Hey all. I’m wondering how this exception

java.lang.NullPointerException: Attempt to invoke virtual method 'float java.lang.Number.floatValue()' on a null object reference

can occur while iterating over a

MutableList<Float

. All

Float

values that are added to the list are

nonNull

; a

Float

value is returned from one function (where the return type is

Float

), used by a different function (where the parameter type is

Float

), and then added to the

MutableList<Float>

. Later I iterate over the list (

for (i in 0 until list.size) list[i]

) and it is here when the exception is thrown, when I’m getting the values from the list. I’ve only ever seen this happen once from crashlytics, but I cannot understand how it even happened once. Values are only added to the list at one point in my execution. After adding values to the list, and before iterating over the list, I may remove the last value in the list (

list.removeAt(list.size - 1)

). Looking at the decompiled code (

((Number)this.list.get(index)).floatValue()

) tells me that the value at that index is null. Am I misunderstanding the stack trace? Could someone please clear this up for me?

Hello everybody, I wanted some help on multi-platform project, on build.gradle.kts jvm target is set to 1.8 but when i run test errors keeps popping out: Cannot inline bytecode built with JVM target 1.8 into bytecode that is being built with JVM target 1.6. any ideas why im getting this?

message has been deleted

Hi all, can i know the plan for kotlin-eclipse plugin ? I see that there is no recent activities on the plugin repo.