kotlinlang #announcements

Hey guys 🙂 I want to design a fluent interface but it seems as if the variance of Kotlin/JVM is not good enough for creating actual DRY code; or maybe I'm missing something?

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sealed class A {
    fun a() = apply { /* doSomething */ }
}

class B : A() {
    fun b() = apply { /* doSomething */ }
}

class C : A() {
    fun c() = apply { /* doSomething */ }
}

B().a().b() // cannot call b() now :(
C().a().c() // cannot call c() now :(

fusdahl

04/20/2018, 10:33 AM

When using the operator overloaded

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to divide big decimals the outcome is kind of unexpected:

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40.toBigDecimal() / 100.toBigDecimal()
0
40.toBigDecimal().divide(100.toBigDecimal())
0.4

This seems to be a result of

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using the half even rounding mode. Does anyone know why this rounding mode was chosen?

Sergio Crespo Toubes

04/20/2018, 10:49 AM

Can i migrate a groovy android project to kotlin class by class? or i have to migrate all project to kotlin for compile? I am getting this error "Unresolved reference" trying to use a groovy class.

adam-mcneilly

04/20/2018, 1:05 PM

Sidebar, let's discuss in 🧵: If I'm initializing an empty list, is there a performance difference between

emptyList()

and

ArrayList()

Michael

04/20/2018, 4:18 PM

Is there a kotlin way to do a string to regex and have it be “Un-greedy” or “lazy”?

Andreas Sinz

04/20/2018, 4:27 PM

@Michael Regex in kotlin is the same as in java and sadly there is no non-greedy modifier in java, you need to use reluctant modifiers https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html

ribesg

04/20/2018, 10:07 PM

Why does this creates TONS of objects, and what should I do to prevent it?

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cache.entries.removeAll {
            val res = now - it.value.first > duration
            if (res) <http://log.info|log.info>("Removing value in cache $name for key ${it.key}")
            res
        }

Fuyang

04/20/2018, 10:09 PM

question: when using lambda on list such as

list.map { process(it) }

, how can I print out the progress? Using onEach and a counter outside?

Dexter

04/21/2018, 1:07 AM

Got it. Also what are the semantics if you trigger an exception in one of the deferred lambdas? I hope you would absorb the exception and execute all the lambdas. Also I would expect the deferred lambdas to be executed in LIFO order.

Andreas Sinz

04/21/2018, 1:16 PM

what library are you using?

lielran

04/22/2018, 1:46 PM

I tried to use

com.github.johnrengelman.shadow

but failed to provide the main-class via

application

block

Juan

04/22/2018, 7:35 PM

What's wrong with

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if (list is ObservableList<Course>)

? it's displaying this error "Cannot check for instace of erased type: ObservableList<Course>"

sujin

04/23/2018, 9:50 AM

How to print query in

Room

? Not the query written in dao but the query generated by room itself.

stackoverflow 6

pankajrai

04/23/2018, 12:02 PM

Do creation of Singleton has been changed now? object MySingleton { val num:Int = 10 } No longer create a private constructor

davidarteaga

04/23/2018, 5:14 PM

Hey guys. I am using coroutines to run several long tasks in parallel, and I would like to time each of the tasks, but considering only the time that the coroutine has actually been executed (that is, excluding the time it was suspended). I haven’t been able to find any info on this yet. Anyone have a suggestion?

warriorprincess

04/23/2018, 5:55 PM

https://codeshare.io/2EbP7O

pavel

04/23/2018, 7:52 PM

I would read

foo.if { bar() }

as return

foo

bar()

is true

gabrielfv

04/23/2018, 7:57 PM

My use case is taking a long stream of functional-like calls. Instead of wrapping everything around an

if

or assigning it all to a variable, I just call it like that:

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data
    .filter { it.hasErrors }
    .map { it.error }
    .any { it is MyException }
    .then { /*Treat that exception*/ }

zpearce

04/23/2018, 8:06 PM

Not as pretty:

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data
    .filter { it.hasErrors }
    .map { it.error }
    .takeIf { it is MyException }
    ?.let { dealWith(it) }

👍 2

John

04/23/2018, 8:11 PM

Just joined the group although still a beginner in kotlin

kschlesselmann

04/24/2018, 6:02 AM

Can I use `data class`es for JPA Entities having equals only on

id

and the other using

val

somehow? In order to generate

equals()

only of

id

it has to be the only argument in the primary constructor.

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@Entity
data class Term(
        @Id
        val id: UUID,

        val name: String
) {

    val definition: Definition = Definition.DEFAULT

    constructor(id: UUID, name: String, definition: Definition) : this(id, name) {
        this.definition = definition
    }
}

I think I'd like to do someting like this …

v79

04/24/2018, 8:44 AM

Can I use a typealias to get around multiple constructors having the same parameter types? e.g.

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typealias Prefix = String; class Form(request: Request, prefix: String) { constructor(request: Request, postfix: String) : this(request, "") }

(class abbreviated!)

🚫 3

😢 1

Yuriy Kulikov

04/24/2018, 8:53 AM

Hello everyone, our team is new to Kotlin (we are used to Java) and since we have to started to write new stuff in Kotlin, we cannot seem to agree on some best practices. Small stuff, mostly: 1. Where to put higher order functions and data classes - is it ok to write them directly in the same file or they have to be moved to a new file? Pro/contra? 2. Extension functions - is it ok to declare member extension functions in classes (i.e. extension functions which have access to class properties)? Or should be prefer higher end extension functions? Example: // declared in the class, access a class property private fun String.toTypeElement(): TypeElement { return processingEnv.elementUtils.getTypeElement(this) } -vs- // declared outside, class property must be passed as a parameter fun String.toTypeElement(processingEnv: ProcessingEnvironment): TypeElement { return processingEnv.elementUtils.getTypeElement(this) } Thanks a lot:-)

edwardwongtl

04/24/2018, 9:29 AM

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data class Response<T>(
  ...
  val data: List<T>
}

Has anyone using moshi to deal with this kind of object? I don't quite seems to find example for doing so..

anli

04/24/2018, 9:39 AM

Hi! Home made (but not by me) annotation results in

lateinit modifier is not allowed on extension properties

error. How to resolve?

chirag

04/24/2018, 10:12 AM

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data
                .mapNotNull {
                    val type = it.asJsonObjectOrNull()?.get("type")?.asStringOrNull()
                    val events = it.asJsonObjectOrNull()?.get("events")?.asJsonArrayOrNull()

                    if (type != null && events != null)
                        type to events
                    else
                        null

                }.toMap()

chirag

04/24/2018, 10:13 AM

due to if else statements

elect

04/24/2018, 10:13 AM

can you confirm me that an

Array<Float>

corresponds to

Float[]

on Java?

karelpeeters

04/24/2018, 10:26 AM

If you're calling it polymorphically it won't be inlined.