@Max Deineko Folding without an initial value is called reduce: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/reduce.html

so its not getting started totally but can u recommend any sources to master kotlin for android development, i know some advanced topics of kotlin - to not write java style - but find it hard to apply in everyday coding. Thanks in advance

i want to use when expression in this kind of situation

when(string){
   null -> ...
   this.length>1 -> ...
   else ->
}

i resorted to this:

when{
   this==null -> ...
   this.length>1 -> ...
   else ->
}

is this idiomatic solution?

e.g.

map.getOrPut(key, { mutableSetOf() }).plusAssign(value)

@Fuyang what do you think?

hello, can someone help me with this error? https://pastebin.com/C5bHMaTq

hello - I have a question - can I use a Map with generics simmilar to that in kotlin?

val objects = FXCollections.observableHashMap<KClass<A: BasicModel>, ObservableList<A: BasicModel>>()

inline fun <reified T: BasicModel> get(): ObservableList<T> {
    return objects[T::class]
}

Hi guys! Is there any way of to implement

invoke

operator to initialize an

enum class

? I tried as an extension function, but the Intellij doesn't seem to see the constructor...

Can anyone suggest few vidoes for getting started?

Either that or

(A.firstOrNull() ?: B.first()).field

. Or just split it into two lines:

val first = A.firstOrNull() ?: B.first()
val field = first.field

lol glad you clarified the spelling 😛

variable?.run{ }

== run this block if this thing is not null? correct?

can Delegates be used to observe changes like RxJava, or Googles LiveData?

Hello 🙂 Pretty new to Kotlin here. I have defined an interface in Kotlin that has a method with a

Long

return type. I am implementing the interface in a Java class, and I would like the return type to be

Long

, but it says it has to be

long

. How can I accomplish this? 🤔

Hullo! I'm trying to make use of the

javax.script

support that was introduced in Kotlin 1.1, however the first line always throws a

NullPointerException

.

val engine = ScriptEngineManager().getEngineByExtension("kts")!!
engine.eval("val x = 3")
println(engine.eval("x + 2"))  // Prints out 5

I'm extremely new to this language and its tooling, is there something obvious I'm missing? I was under the impression that it would sort of just "come with" the language but I wouldn't be surprised at all if I need to install a dependency or two. My google skills have been failing me unfortunately.

the only way of having backing properties is doing something like this?

class C {
    private val _elementList = mutableListOf<Element>()

    val elementList: List<Element>
         get() = _elementList
}

what would be the use case of apply here? (actually curious)

hey, can someone clarify this line on @antonioleiva’s site: "First thing to clarify is that MVP is not an architectural pattern" enerywhere i have seen it's called an architectural pattern...

Hi All. Do any of you know of some good resources to get up and running with Kotlin? My last experience with the JVM was at University, that was Java 6. Now we are at Java 10 o.o. I am a Web guy, I use mostly Python, PHP and Go at work so I am spoilt when it comes to the simplicity of creating HTTP/JSON/RESTish apis. My understanding is that the 'Spring' framework is used for web dev? But it seems to be a 6000 pound gorilla for a hello world api...is there something like the equivilent of golangs net/http library for Kotlin/Java? any help would be much appreciated.

This forks the heavy stuff into another thread allowing the UI to update... The only trouble it the CommonPool can't access the UI or update/change it...

Hey guys, which testibg framework would you choose right now? Im familiar with junit but heard about spek lately - is it as straight forward as junit 5 is? Maybe something else is worth a shot?

fun getStringLength(obj: Any): Int? { //

obj

is automatically cast to

String

on the right-hand side of

&&

if (obj is String && obj.length > 0) { return obj.length } return null } Why is it Int here?

If I don't do the flatmapelements method it performs as the java code. Only the flatmapelements produce errors.

Android: I am attaching the same

textChangedListener

to multiple input fields. Currently I have this:

withdraw_input.textChangedListener {
    afterTextChanged {
        validateInput()
    }
}

reg_number.textChangedListener {
    afterTextChanged {
        validateInput()
    }
}

I cannot figure out how to extract the listener to a variable and then re-use it, instead of defining the same listener multiple times. I guess it’s just a syntax issue 🤔 Any hints? 🙂

any recommended xml parsing library for kotlin?

such as

if(isNull(someString)) { someString.length } else { someString.length }

, the first

someString.length

would give an error or something

Makes sense, the interfaces really are defined in common, but the classes are all

expect

.

@bjonnh I'm on a JVM project and I can only import interfaces from that package.

#SWIFT
enum NumberCategory {
   case Small
   case Medium
   case Big
   case Huge
   init(number n: Int) {
    if n < 10000 { self = .Small }
    else if n < 1000000 { self = .Medium }
    else if n < 100000000 { self = .Big }
    else { self = .Huge }
   }
}

How I can achieve something like this in kotlin? Just to illustrate my problem I have a bunch of business logic conditionals that I want to convert to a type and send it to my view, I’m not even sure if this is the best solution or I stick with boolean methods

Create a normal enum, in the companion object put a function

fromNumber

or something like that.