kotlinlang #stdlib

inline fun CharSequence.forEachCodePoint(
    start: Int = 0, end: Int = length,
    action: (index: Int, codePoint: Int) -> Unit
) {
    var i = start
    var codePoint: Int
    while (i < end) {
        codePoint = Character.codePointAt(this, i);
        action(i, codePoint)
        i += Character.charCount(codePoint)
    }
}

👍 2

LeoColman

06/07/2020, 9:01 PM

Is there a particular reason that Array isn't an IterablE?

bod

06/11/2020, 5:01 PM

Hello, World! What would be the easiest way to get an "inverted" version of a Map (by that I mean the values become the keys and vice versa)?

rrva

06/24/2020, 1:57 PM

Give me an elegant way to express “Is T1 more than 15 minutes ago” in Kotlin. Is anything happening at https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.time/ ? I am using ChronoUnit.MINUTES.between now, but thinking is there is something even more readable

rrva

06/24/2020, 2:56 PM

Is there something like https://api.dart.dev/stable/2.8.4/dart-core/Iterable/where.html which makes you express things better than with

filter

filterNot

rrva

06/25/2020, 7:11 AM

Can I create a ExperimentalTime TimeMark from an OffsetDateTime using something like this or is it completely wrong usage/thinking around TimeSources?

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@OptIn(ExperimentalTime::class)
class DateTimeSource(val time: OffsetDateTime) : AbstractLongTimeSource(unit = DurationUnit.MILLISECONDS), TimeSource {
    override fun read(): Long {
        return time.toInstant().toEpochMilli()
    }
}

Hullaballoonatic

07/05/2020, 9:33 PM

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fun <C : Comparable<C>> C.coerceAtMost(maxValue: C) = if (this > maxValue) maxValue else this
fun <C : Comparable<C>> C.coerceAtLeast(minValue: C) = if (this < minValue) minValue else this
fun <C : Comparable<C>> C.coerceIn(minValue: C, maxValue: C) = coerceAtLeast(minValue).coerceAtMost(maxValue)

Also

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fun <C : Comparable<C>> min(vararg elements: C): C
fun <C : Comparable<C>> max(vararg elements: C): C

I'm a bit surprised these methods aren't part of stdlib of any languages i know of. Is there a reason I haven't considered?

Jamy

07/06/2020, 11:55 PM

Hello ! Why is it useful that toString can return a “null” string if it is applied to null? I may sound silly to you, but I didn’t know. As a result, I just passed some time looking for why

val a = b?.c.toString()

where

b == null

results

a != null

since in this case

a == "null"

. So to get what I want, I have to write

val a = b?.c?.toString()

. It’s not a problem, I just don’t understand the purpose.

😐 3

louiscad

07/08/2020, 12:15 PM

Would you use such functions?

fun List<E>.subListAfterFirst(element: E): List<E>

fun List<E>.subListAfterLast(element: E): List<E>

They could also take a predicate instead of an element. Maybe there's already a good alternative that I didn't think of or found?

bbaldino

07/10/2020, 10:28 PM

Is it possible to generically create an enum from an instance of

KType

(of the enum) and a string (of the enum value) ?

diego-gomez-olvera

07/17/2020, 11:18 AM

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public fun <T> MutableList<T>.removeAll(predicate: (T) -> Boolean): Boolean = filterInPlace(predicate, true)

private fun <T> MutableList<T>.filterInPlace(predicate: (T) -> Boolean, predicateResultToRemove: Boolean): Boolean {
    if (this !is RandomAccess)
        return (this as MutableIterable<T>).filterInPlace(predicate, predicateResultToRemove)

    var writeIndex: Int = 0
    for (readIndex in 0..lastIndex) {
        val element = this[readIndex]
    ...
        if (writeIndex != readIndex)
            this[writeIndex] = element
     ...
}

It seems

CopyOnWriteArrayList.removeAll

does not copy on write but mutates in place instead

nkiesel

07/17/2020, 8:07 PM

Should there be standard support to sort lists of Strings locale-dependant? Something like

fun Iterable<String>.sortedWith(collator: Collator) = this.map { collator.getCollationKey(it) }.sorted().map { it.sourceString }

Daniele B

08/08/2020, 8:02 PM

what is the best way in the stdlib (without Java) to convert a number to a string with thousands separated by commas? e.g. “2029292” which becomes “2,029,292"

natpryce

08/09/2020, 8:40 AM

Q: Does the stdlib have an associate-like function that takes a function to merge elements with duplicate keys (similar to Collectors.toMap in Java Streams)?

Marc Knaup

08/09/2020, 1:49 PM

It’s confusing that

Flow.toList()

closes the Flow but

Stream.toList()

doesn’t close the Stream. Is that inconsistency intentional?

Daniele B

08/10/2020, 4:06 PM

I would like to format a Float to a String with 1 decimal, but I can’t find the way. If I write this:

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val myString = "%.1f".format(myFloat)

it tells me that the function

format

doesn’t exist?

Matteo Mirk

08/13/2020, 8:56 AM

Is there an equivalent of

java.text.NumberFormat

in Kotlin multi-platform stdlib? I can’t seem to find any…

🚫 3

Fleshgrinder

08/15/2020, 3:56 PM

Any particular reason why

buildList

and friends are still experimental in Kotlin 1.4?

rrva

08/17/2020, 8:36 AM

given a list [a, b, c, d], what is the idiomatic way to split it into two parts at a given index? Using subList feels clunky. I would like to write list.splitAt(2) to get [[a, b], [c, d]

Esa

08/20/2020, 11:36 AM

Hi there, I have a couple of extension functions for

Iterable<T>

that has been very useful to me personally, and I wish to make a contribution to the stdlib with those. 🙂 I read through this link and was suggested to make my plans known to #kontributors, however they sent me here. So here's what the functions are basically:

list.validatedFold

- this is a function that iterates through the elements of an ordered list, and verifies that elements

and

n+1

pass some validation function. returns true if all elements pass, or false on the first element that does not pass (early return). list.flatMapIndexedNotNull
- essentially what the name says, it was relevant for me in one case and I didn't find it in the stdlib. Do you think these are appropriate contributions?

Daniele B

09/03/2020, 11:00 AM

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fun main() {
    val number = 0.001 * 0.001
    println(number.toString())
    // prints 1.0E-6
}

How can I make it print “0.00001” ?

diego-gomez-olvera

09/15/2020, 10:40 AM

hello! I wonder why

Reader

extensions do not use

@JvmThrows

https://github.com/JetBrains/kotlin/blob/master/libraries/stdlib/jvm/src/kotlin/io/ReadWrite.kt#L120

elect

09/24/2020, 8:53 AM

String.getOrNul(index: Int): Char

where

nul

\u0000

Daniele B

10/07/2020, 6:32 PM

how to get the current unixtime in standard library?

rnett

10/15/2020, 3:40 AM

This may be more appropriate for #compiler, but I've noticed there's some quite nice utilities in

org.jetbrains.kotlin.utils.addToStdlib

in the compiler artifact. Are these things that will be added to the stdlib soon? Because several (especially

cast

and

safeAs

, for me) are quire nice

spand

10/22/2020, 6:54 AM

Is there a common stdlib function I am missing for converting a codepoint to a String ?

spand

10/23/2020, 11:28 AM

Is either the implementation or the documentation wrong for

Map<K, V>.getOrElse

? on ie.

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mapOf("1" to null).getOrElse("1") { error("missing") }

Will throw an error yet

containsKey("1")

return

true

. The docs says: ... or the result of the [defaultValue] function if there was no entry for the given key. There is an internal

getOrElseNullable

that would fix it but I assume it was not chosen for a reason

➕ 3

Mark

10/26/2020, 6:38 AM

I have a list of

() -> Item

lambdas and I want to map it like

map { it() }

. Is it possible to write this using a function reference? I was guessing something like

map((()->Item)::invoke)

mbonnin

10/30/2020, 2:12 PM

Reposting here as I just found out about this channel https://kotlinlang.slack.com/archives/C0922A726/p1604066165235100

MiSikora

11/01/2020, 1:53 PM

Would it be possible to have a non inline equivalent of enumValues()? Something along the lines of

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public fun <T : Enum<T>> enumValues(enumClass: KClass<T>): Array<T>