what is the best way to force the initialization of the fields on an object, ex

object Config {
    val port = System.getenv("PORT") ?: 8080
}

How can I make

MutableList.map{ ... }

to return

MutableList

instead of

List

Is there no overhead calling

toMutableList()

again after mapping?

is there such a thing as diffing two objects?

Hello everyone. Is there any lib / framework similar to Microsoft Blazor?

I'd like to implement a queue of functions where a function can be added, called after x seconds, then removed. I don't want to have to specify what arguments are provided at call-time, but rather when they are being added to the queue... I believe I can define the queue like

val queue: Queue<() -> Unit> = LinkedList()

, but I don't think the Queue type will do what I need as I described above. Any recommendations?

Where can I learn more about annotations? I'm reading through the docs on the Kotlin website but not finding much that's useful to me. Here's what I'm trying to do: I want to annotate functions that belong to a class. Those annotated functions when called should, instead of being executed right away, be added to a BlockingQueue that belongs to the containing class. So far I've figured out that I can make a

annotation class Queueable

with a Target of

AnnotationTarget.FUNCTION

. I'm not finding any documentation anywhere on how I can accomplish the rest of what I'd like to do though... In Python, for example, I can annotate a function and access it's arguments and other properties about it since the annotation wraps the function. Am I thinking about annotations incorrectly in Kotlin?

open class SuperClass {
    override operator fun equals(other: Any?): Boolean {
        return super.equals(other)
    }
}

class ExtendedClass : SuperClass() {
    override operator fun equals(other: Any?): Boolean {
        return super.equals(other)
    }
}

Error:(9, 14) Kotlin: 'operator' modifier is inapplicable on this function: must override ''equals()'' in Any

so apparently this doesn't compile unless I remove the

operator

keyword from `ExtendedClass`' implementation is this intended behavior? this seems... a bit weird and unintuitive to me

Say I have an operation that may return a list of things or a null (interop with a library). What would be idomatic in kotlin to do something if the result is null or do another thing (map) if the result is not null (and contains elements). I'm thinking "either-or", as in either do a "default" operation if the result is null or the "or" operation if the result is not null and the list contains elements?

what if said function is an extension? e.g.

fun OtherType.myFunc(...)

, what's the syntax to choose the right super extension function for my override?

Suppose I have:

abstract class AbstractClass (
  val a : String? = null,
  val b : String? = null,
  val c : String? = null,
  val d : String? = null,
  val e : String? = null,
  val f : String? = null,
  val g : String? = null
)

class MyClass (
  a, b, c, d, e, f, g,
  val h : String? = null,
  val i : String? = null
) : AbstractClass(
  a, b, c, d, e, f, g
)

Is there any kind of shorthand to avoid having to repeat a,b,c,d,e,f,g twice when defining the class?

Please help.

is there any built in construct to deal with something like this?

var initialized = false
if (!initialized) {
    ...
    initialized = true
}

Anyone have articles/docs/samples of using OkHTTP/other network requests with coroutines? I'm trying to make a simple application that calls out to HTTPBin as a producer and sends the UUID responses back through a channel.

fun doSomething() {
  // return instance of whatever is between the angle brackets below
}

val x = <MyType>doSomething()
val y = <MyOtherType>doSomething()

How should the signature of doSomething look?

Or is there some other clever way to solve this?

Hi, anyone know why I am getting this as an error in kotlin but not in java? It is not allowing project to build either

How would I do something like “I have a superclass (which has some logic in a lifecycle method that I want to trickle down to fragments), and I have an interface. I don’t want(?) the superclass to implement the methods in the interface, but everything that inherits from the superclass should implement the interface”.

Can I pass an overloaded function as a parameter to another? Eg.,

class Foo {
    fun bar(p1: Int)
    fun bar(p2: String)
}

Is it possible to reference one of the

bar()

overloads as a function argument?

Hi all! I'm really new with compilers / kotlin compiler plugin / JVM bytecode then probably this is a very newbie question: is it possible with kotlin compiler plugin generate a function bytecode changing its name? Example I have this function:

@TestAnnotation("bar") fun foo() {}

And my plugin would change its bytecode to something like:

fun foo_bar() {}

And by doing that, compiler would support many functions with the same name? like:

@TestAnnotation("bar") fun foo() {}
@TestAnnotation("bar2") fun foo() {}
@TestAnnotation("bar3") fun foo() {}

quick question, do you people (especially those working with IntelliJ): - always specify types explicitly, - never specify them when IntelliJ can infer them (since it will show them as hint text instead, at least with the IDE's default options) - something in-between? (like, only for interface/abstract/open methods' return types since they define a contract) i suppose it's mostly a matter of preference in some cases, but i find myself hesitating a bit when writing super simple/closed methods that return a boolean, or when using things such as

List#toMutableList()

(it seems a bit overkill to mark the resulting variable as a

MutableList

then), so i ended up going for the 3rd approach (aka, only for overridable stuff), but i was curious if there was some kind of consensus on this

Is there a way to not have to say !! here?

Hello, IntelliJ doesn't allow me to run

fun main() {}

without the args array (works with it), why is that?

can you use when in a string template like if else

Hi, I would like to ignore a warning the compiler is throwing:

Type mismatch: inferred type is Cursor? but Cursor was expected

I can ignore it safely but de IDE does not provide me any suggestion to add a

@SupressWarning`

Hi, is ktlint the go-to formatter (the 'prettier' or gofmt) of kotlin? My team is starting to use kotlin, and such a tool would help a lot to keep things tidy 🙂

This message was deleted.

So my understanding of extension functions is that you can add a function to an existing library as a static function. I've made this:

fun System.currentTimeSeconds(): Long {
    return System.currentTimeMillis()/1000
 }

and yet I can't do System.currentTimeSeconds(). Am I missing a concept or can you not do extension functions on System?

hi guys, one thing that i curious about

and

&&

for example:

val a = 3
        val b = 4
        val c = 5
        val d = 3

        val result1 = b == c && a == d

        val result2 = (b == c) and (a == d)

1) the result2 if we write

val result2 = b == c and a == d

will not work. not sure why 2) For result1 because the b==c is false. so will not run a==d case. but result2 will get false false so finally will be false. which means result1 only perform one time check and result2 perform 2 times check. Is my understanding correct?

Is there a way to get the class of an object that extends another object? For example,

class Car: Vehicle()
...
getObjectChildClass(Car())
...
fun getObjectChildClass(obj: Vehicle) {
     // From here I want the to know if it's a Car or some other class that extends vehicle, like Truck.
}