kotlinlang #announcements

Not sure if this is the right place to ask, as it involves a third party... But it's also related with the lang. I have a problem with Gson lib, that the api can send empty string as a date. I declared this adapter to tell Gson how to deserialize a date:

registerTypeAdapter(Date::class.java, DateDeserializer())

So when the object has a non optional

Date

, it's clear that I should throw an exception if it gets an empty string. But when

Date

is optional, I'd like to map the empty string to

null

, i.e. the date will just be assigned

null

. Not sure how to do that. It relates with lang, in that the deserializer is defined like this: `JsonDeserializer<Date>`but I need it to work with

Date?

basically. I can of course create a getter in my object that deserializes the date if present, but I'd like to do this directly with the parser, not "outside".

Sam Schilling

01/21/2020, 4:58 PM

Is using an upper-bound generic any different from just using that super type directly? E.g.,

open class Animal { ... }

// Using upper bound generic
fun <T: Animal> print(animal: T) { ... }

// Using type directly
fun print(animal: Animal) { ... }

It seems in both cases any subclasses of

Animal

will work with the function call. In which case the second option seems more readable and condensed if they function identically.

Sandy

01/21/2020, 5:32 PM

I would like to like to write a regex to replace unicode characters in string. Was trying something like str.replace("\\\\u\\d{4}", "")

Wesley Acheson

01/21/2020, 5:44 PM

Okay I know you can have sealed classes for a when check to verify that you are covering all branches. is the reverse possible say given a string input I output all sealed classes under a hirachy? I'm guessing no the type checker can't verify

LeoColman

01/21/2020, 7:41 PM

Hey guys! Is Kotlin JS deprecated? Or are people using it actively?

luke

01/22/2020, 4:07 AM

Anyone any good with Regex? Struggling with this.

1914   1    5.9     0.9    ---     48.3    ---

What I have so far:

([\d]+)\.*([\s]+)

I just want to extract all the non-whitespace values into an Array.

AnnoymousGiraf

01/22/2020, 4:15 AM

Hi, as any one encounter this type of class def and can explain the pattern

Class A cosntructor(...) : (String) -> B {

}

user

01/22/2020, 12:33 PM

Kotlin Census 2019: Call for Respondents You can read this blog post in other languages: The new edition of Kotlin Census is here! By the end of 2019, more than 4 million people had used Kotlin. This is a great number of people, and of course, … Continue reading →

iex

01/22/2020, 3:02 PM

Hi folks! Is there a functional way to write this?

for (handler in handlers) {
    if (handler.handle(uri)) break
}

René

01/22/2020, 7:04 PM

Has someone an working example of a mocked class where you want to verify that one given method was called once? I tried

verify(sut).someMethod("example")

, but that throws always 3 invocations (two other where on other methods). I have right now no idea how to fix that test

David Glasser

01/22/2020, 7:35 PM

I'm trying to understand why it's legal to call a function whose generic type is reified from another function whose generic type is not reified. Something like

inline fun <T : Any> foo(X<T>): List<T> {
  return objectMapper.readValue(xxx)
}
inline fun <reified T> ObjectMapper.readValue(content: String): T = ... # from jackson kotlin

How does the compiler create the reification of the T in the nested function if it's not reified in the outer function?

Ellen Spertus

01/22/2020, 7:59 PM

Is there a more elegant way to write this (besides writing a helper method):

var method: String? = null
try {
    method = jsonResponse.getString("method")
} catch (exception: JSONException) {
    Log.i(TAG, "No method provide by server.")
}

Michael Friend

01/22/2020, 10:20 PM

When making a safe cast on an object that might be null, is there a difference between

val casted = nullable as? String

and

val casted = nullable as String?

? They both smart cast to

String?

but do they both give null if

nullable

is null and

nullable

casted to a string (assuming the cast is possible)? I know using

as?

returns null if the cast fails and i assume option 2 would throw an exception, is that the only difference?

trathschlag

01/23/2020, 8:42 AM

Is there an ergonomic way to make constructors file-visible only?

ribesg

01/23/2020, 10:29 AM

var result: Result<T>? = null
// ...
return result!!.getOrThrow() // Expression of type kotlin.Result cannot be used as a left operand of '!!'

What is that supposed to mean? Why do I have to write

(result as Result<T>).getOrThrow()

for it to compile?

Marcin Wiśniewski

01/23/2020, 10:30 AM

Hi, during project compilation (maven 3.6.3, kotlin 1.3.61) I received following error:

[INFO] Possible cache corruption. Rebuilding. <http://com.intellij.util.io|com.intellij.util.io>.PersistentEnumeratorBase$CorruptedException: PersistentEnumerator storage corrupted /builds/swb/api/api/target/kotlin-ic/compile/caches-jvm/inputs/source-snapshot.tab
<http://com.intellij.util.io|com.intellij.util.io>.PersistentEnumeratorBase$CorruptedException: PersistentEnumerator storage corrupted /builds/swb/api/api/target/kotlin-ic/compile/caches-jvm/inputs/source-snapshot.tab
    at <http://com.intellij.util.io|com.intellij.util.io>.PersistentEnumeratorBase.<init>(PersistentEnumeratorBase.java:221)
    at <http://com.intellij.util.io|com.intellij.util.io>.PersistentBTreeEnumerator.<init>(PersistentBTreeEnumerator.java:73)
    at <http://com.intellij.util.io|com.intellij.util.io>.PersistentEnumeratorDelegate.<init>(PersistentEnumeratorDelegate.java:47)
    at <http://com.intellij.util.io|com.intellij.util.io>.PersistentHashMap.<init>(PersistentHashMap.java:163)
    at <http://com.intellij.util.io|com.intellij.util.io>.PersistentHashMap.<init>(PersistentHashMap.java:152)
    at <http://com.intellij.util.io|com.intellij.util.io>.PersistentHashMap.<init>(PersistentHashMap.java:143)
    at <http://com.intellij.util.io|com.intellij.util.io>.PersistentHashMap.<init>(PersistentHashMap.java:135)
    at <http://com.intellij.util.io|com.intellij.util.io>.PersistentHashMap.<init>(PersistentHashMap.java:128)

Problem occurs only on Gitlab-CI pipeline. Compilation on local machine works well. Can anybody help me to fix it?

👀 1

ribesg

01/23/2020, 11:13 AM

Found a bug, curly braces are required here. Autofix removes the label

Michael de Kaste

01/23/2020, 1:56 PM

play and try kotlinlang.org is down?

Ianmedeiros

01/23/2020, 5:46 PM

How do you guys handle object serialization in the context of Sealed classes? This is a behaviour that we get for “free” with enums.

sealed.txt

tipsy

01/23/2020, 8:45 PM

i have a colleague who makes typealias for everything, like:

typealias Address = String
typealias Age = Int

when i see these typealiases used in signatures, i always assumed they're classes is there a guideline on this? i personally find it very confusing, but it might just be because it's unfamiliar

🤔 4

voben

01/24/2020, 8:44 AM

Can I catch 2 exceptions at once in kotlin like we do in java?

// Java code
try {
    return doDangerousThing();
} catch (ExceptionA | ExceptionB e) {
    e.printStackTrace();
}

GarouDan

01/24/2020, 9:57 AM

Hi, In order to configure my build I need to expose some private methods from a 3rd party plugin. Can I do that using Kotlin extensions? The plugin in question is the

xcode-compat

, and the method that I’d like to expose is

setupTask

(which is available here: https://github.com/Kotlin/xcode-compat/blob/6633fe0696c38c9eee2f789164b8b945910fdc13/xcode-compat/src/main/kotlin/org/jetbrains/kotlin/xcodecompat/XcodeCompatPlugin.kt#L27) Please also note that this method will depend on other private ones. I tested copying and pasting the plugin locally and then applying it, it works after that, but I don’t know if I can do that without forking the plugin. Can we?

redenergy

01/24/2020, 11:44 AM

How to debug and fix issues with Database class initialization like this? I have included exposed-jdbc dependency but the exception is still here. Quick googling yielded only one issue on github without a proper solution. I suspect it has something to do with different classloaders but I am not sure where to start

java.lang.NoClassDefFoundError: Could not initialize class org.jetbrains.exposed.sql.Database
	at gloomyfolken.bundle.common.mysql.MysqlContext.<init>(MysqlContext.kt:33)
	at gloomyfolken.bundle.common.mysql.MysqlWorkerThread.openConnection(MysqlWorkerThread.kt:98)
	at gloomyfolken.bundle.common.mysql.MysqlWorkerThread.run(MysqlWorkerThread.kt:109)
Caused by: java.lang.IllegalStateException: Can't load implementation for DatabaseConnectionAutoRegistration
	at org.jetbrains.exposed.sql.Database.<clinit>(Database.kt:64)
	... 3 more

ylemoigne

01/24/2020, 12:25 PM

Edited question : Is there any syntax that allow for a premature return in when case block ? If a such thing is possible, what it look like ? (Original question : Hello, I have difficulties to find the right syntax (jump label ?) to return from a
when
clause) Eg :

fun main() {
    val myShortCutCondition = true
    val s = when(2){
        1 -> {
            if(myShortCutCondition){
                // return "shortcut" // for `s` value
            }
            
            // longCode
            
            "1"
        }
        2 -> "2"
        else -> ""
    }
}

natpryce

01/24/2020, 2:56 PM

Jackson can parse YAML to a tree of JsonNode objects.

😮 1

Georgi Naumov

01/25/2020, 3:22 PM

Would you suggest how to make that code better: https://gist.github.com/gonaumov/567f756fba95ad6b30bbab575b2f2fba

Nick Halase

01/25/2020, 8:32 PM

Does Jetbrains have a place for us to discuss the Space EAP? I'm in the middle of setting up Space for my workplace and I have general questions about best-practice that I can't find answers to in the documentation (yes I realize this is EAP access).

poohbar

01/26/2020, 2:27 AM

Is there any built-in for

String

to ensure that a string ends with a certain character? Also called "append if missing" in some libraries. e.g.

foo("word", ".")

word.

foo("word.", ".")

word.

otakusenpai

01/26/2020, 8:32 AM

Hi, Just created a mpp prohect using gradle in IDEA. How do i add another module named "common" module?

otakusenpai

01/26/2020, 1:57 PM

I was reading someone's code for some thing and found this strange class definition

class Usage(from: List<UsageArgument> = listOf(), val runsAt: List<RunAt> = listOf()) : List<UsageArgument> by from {
    override fun toString(): String {
        val result = joinToString(" ") { it.format() }

        return if (result.isBlank()) "none" else result
    }
}

can anyone explain this to me? especially the parameters of the class def and the ending "by from". what does it mean? the use case is like a list or something i suppose?

Title

otakusenpai

01/26/2020, 1:57 PM

I was reading someone's code for some thing and found this strange class definition

class Usage(from: List<UsageArgument> = listOf(), val runsAt: List<RunAt> = listOf()) : List<UsageArgument> by from {
    override fun toString(): String {
        val result = joinToString(" ") { it.format() }

        return if (result.isBlank()) "none" else result
    }
}

can anyone explain this to me? especially the parameters of the class def and the ending "by from". what does it mean? the use case is like a list or something i suppose?

Chills

01/26/2020, 2:00 PM

strange?

Foso

01/26/2020, 2:01 PM

"by" is a keyword for Delegation https://kotlinlang.org/docs/reference/delegation.html

Chills

01/26/2020, 2:11 PM

delegation is a hard topic

to wrap your head around it , look at delegation pattern before hand.

Ray Eldath

01/26/2020, 6:49 PM

off-topic: i remembered KotlinConf 2018 Closing Panel someone pointed delegation as their most hateful feature. and in ktconf 2019 Andrej says delegation is what he want to redesign most, IIRC.

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