I was under the impression that

const val

can not be assigned any function calls, but as I found out from this SO question it's actually possible for some functions: https://stackoverflow.com/questions/44921746/what-can-be-expressed-in-a-compile-time-constant-const-val From the given answers, it's not completely clear to me what is the reason for that. Is it because these function calls are not actually translated to function calls by the compiler, but replaced for operators?

I don't have much experience in Kotlin, but doesn't the exception

laneinit

throws defeat the purpose of null safety?

Why is it necessary to have a

Observer

prefix in the second line below in order for SAM conversion to work, but not in the first line? The last parameter has identical declarations in these two cases.

MutableLiveData<String>().observeForever({  })        // No 'Observer' prefix necessary
    MutableLiveData<String>().observe(this, Observer {  })        // 'Observer' prefix necessary!

    // Java declarations
    public void observeForever(@NonNull Observer<? super T> observer) {
    public void observe(@NonNull LifecycleOwner owner, @NonNull Observer<? super T> observer) {

a clarification: file-level variables are not referred to as "global variables", right? They are properties

can anything else be assigned to a

const val

besides literals and other `const val`s?

Is there any one who know how to append text file. I m making access log file. My code only write once to a file, how to append text?

class AccessLog: Serializable {
    companion object {
        var LOG = "/usr/local/logs/access_log"
        @Synchronized
        fun write(domain: String, remoteIp: String, userId: Int) {
            File(LOG).bufferedWriter().use { out ->
                out.write("""domain: $domain    remote_ip: $remoteIp    user_id: $userId    """)
            }
        }
    }

A

const val

1) optimizes the generated bytecode 2) can be used in annotations. My question: are there any other benefits over just using

val

that I am missing?

This message was deleted.

Why does

Foo : Bar<Quax>

require

Quax

to be public, i.e. internal not allowed?

Foo is final, I dont get it

😀 Hello everyone am victor and am new to kotlin, a new resources or Tutorial to help a novice like me grow🤗

FAILURE: Build failed with an exception. * What went wrong: Execution failed for task ':compileKotlin'.

Kotlin could not find the required JDK tools in the Java installation '/usr/lib/jvm/java-8-openjdk-amd64/jre' used by Gradle. Make sure Gradle is running on a JDK, not JRE.

* Try: Run with --stacktrace option to get the stack trace. Run with --debug option to get more log output. Run with --scan to get full insights. * Get more help at https://help.gradle.org Deprecated Gradle features were used in this build, making it incompatible with Gradle 6.0. Use '--warning-mode all' to show the individual deprecation warnings. See https://docs.gradle.org/5.5/userguide/command_line_interface.html#sec:command_line_warnings

Hey, I'm relatively new to kotlin, for now its very smooth experience for me, but one thing that bothers me is that there is no package-private modifier, so does it mean that kotlin doesn't need it or its one of the downsides that should be fixed?

I'm confused by this sentence in the docs:

If a Kotlin file contains a single class (potentially with related top-level declarations), its name should be the same as the name of the class, with the .kt extension appended.

Because IntelliJ/AS removes the

.kt

if the file contains only 1 class

Hi folks, I’m working on a pretty standard spring boot / kotlin app, where we’ve an api written in kotlin and a frontend in react. We just did our first coroutines here, and I’ve some questions about it. The usecase was to optimize a very slow function, and we did that by adding 3

CoroutineScope(EmptyCoroutineContext).async {}

calls on the 3 slowest components of that function, and awaiting the results at the end, as well as optimizing the order of the calls. However, this means that function and every function up to the controller /endpoint now has a

suspend

qualifier, as well as the controller having a

runBlocking {}

wrapped around the function (it doesn’t seem like a major issue to me, that endpoint has about a 3.5s runtime now).. And as this is my first foray into coroutines, I’m sort of anxious there’s some drawbacks to this I’m missing.

Is there a way to check if lambda val bodies are the same? I've tried checking by hashCodes, but those are still different for identical lambdas

wouldnt it be better if defult access-modifier was internal rather than public? I think it would make our code more encapsulated

I have below method in a companion object, which should extract a specific implementation class Wrapper depending on the Kotlin primitive type.

fun extractRealClass(valueClass: Class<*>): Class<out PrimitiveWrapper<*>>? {

    return when (valueClass) {
        
        Boolean::class.java -> BooleanWrapper::class.java
        
        Int::class.java -> IntWrapper::class.java

        String::class.java -> StringWrapper::class.java

        else -> null
        
    }

}

// where PrimitiveWrapper is defined as:

open class PrimitiveWrapper<T>(val value: T) {... Above func lives in this class companion}

class BooleanWrapper(value: Boolean) : PrimitiveWrapper<Boolean>(value) { ... }

class IntWrapper(value: Int) : PrimitiveWrapper<Int>(value) { ... }

on another class

Entry

I have this:

Entry<T: Any?>(
    private val key: String,
    private val clazz: Class<T>
) {

override fun getInstance(): T? {

    // It always return null when calling above mentioned func.
    val primitiveClass: Class<out PrimitiveWrapper<*>>?
                = PrimitiveWrapper.extractRealClass(clazz)

}

}

Whenever I call the

PrimitiveWrapper.extractClass(clazz)

with the save class info it always return null. I tried many things and no matter what in the

when

block the coming class always print like

int

or

<http://kotlin.Int|kotlin.Int>

but never

java.lang.Integer

. Could some body shed some light?

Hey guys! Wondering how does Kotlin allows access to members of private anonymous object in a class?

I don't have to initialize a property right away if I use

lateinit

or override the

getter

. Any other ways to get around immediate initialization? (It's a theoretical question)

Kotlin has a

Map/MutableMap

which is a

LinkedHashMap

which preserves the insertion order unlike

HashMap

. In Java/Android, if one is used to using

HashMap

then I would think I can continue using

Map/MutableMap

in Kotlin. Is that correct?

Can delegating to an interface in a class override some of the functions and members that the actual base class of my class inherits

i cant pass this out of the constructor

Where’s a good place for me to learn about

Flow

? I have not used React so lack that background, although I am familiar with streams from functional programming and have experience with asynchronous callbacks.

do you consider the "class header" = name +

class

keyword + primary constructor or only the primary constructor? The Kotlin Docs use the latter definition (+ type parameters) but that's not what I have in mind

I created a Kotlin project with the template "Mobile Shared Library | Gradle", but I don't have the (expected?) gradle-wrapper.jar file in the gradle/wrapper folder. Is it only a question of project configuration? Thanks in advance.

hey can anyone tell me why when I try declare List of enums I get error

No type arguments expected for class List

I'm using ktor.io library. I want to know how to setup ping sending in websocket from client side to the server every interval defined in the server side. I tried to find docs but there weren't any examples of ping-pong. Somebody can help?

when I put an

init

block under a property I can initialize it there. This doesn't seem to work anymore if this property has a setter. Is that correct?

How can I get rid of

!!

in below code without getting compilation errors and without getting ugly code? Edit: And without recursion

class Node(val child: Node?)

fun Node.getLeaf(): Node {
    var candidate: Node = this
    while (candidate.child != null) {
        candidate = candidate.child!!
    }
    return candidate
}