kotlinlang #getting-started

I want to write an extension method for a list that returns a new list with any null items replaced by a default value. I'm having trouble with the generics. There is one generic for the list and there is another generic for the replacement item. How can I specify this relationship between the two generics? I think this is close:

fun <C: Any, T: C?> List<T>.nonNull(sub: C) = map { it ?: sub }

. However, the compiler can't infer the type of C if there is a null in the list. For example, this doesn't compile:

val x = listOf("x", null).nonNull("y")

. You have to explicitly specify the types:

val x = listOf("x", null).nonNull<String, String?>("y")

. Is there something wrong with my method signature that prevents the compiler from inferring the types?

henrik

11/22/2018, 8:56 AM

fun toMap(): Map<String, Double> = mapOf("key" to nullableDouble1, "key2" to nullableDouble2).filterValues { it != null }

complains that "expected

Map<String, Double>

but found `Map<String, Double?>`". Is there an easy way around this other than appending

as Map<String, Double>

Sartori

11/22/2018, 4:44 PM

Hi guys, anyone know if is possible access that variable like this? I try to see the auto complete but the variable does not appear 😞

-.kt

🙅‍♂️ 1

jojo.lichtenberger

11/24/2018, 1:50 PM

It's from Vert.x with their Kotlin API

dewildte

11/24/2018, 7:57 PM

let {}

is kinda cryptic.

jschneider

11/24/2018, 7:59 PM

Why is there not "it" in when?

liminal

11/25/2018, 6:27 PM

what are some good examples of

takeIf {}

elye

11/26/2018, 6:37 AM

Hi What’s the different between the two below?

(origin as? Implementor)?.someFunction()

(origin as Implementor?)?.someFunction()

febs

11/26/2018, 12:50 PM

Normally you can't declare a var without assigning it a value; unless you state that it is a "lateinit" var. You can't declare a val withoutu assigning it a value too; but you can use "by lazy" to achieve that. BUT THEN Why in a { catch (e: Exception) } block I am allowed to define a val or a var and then assign it afterwards, without the need of "lateinit" nor "by lazy"?

11/26/2018, 3:36 PM

foo(first : SomeObj = validSomeObj()) : Bar = foo(first.toString())
foo(first : String = validSomeObj().toString())  : Bar = Bar(first)

looks like this

serebit

11/26/2018, 6:07 PM

@dG I’ve seen that as well. Making one of the functions into a block body fixes it, for some reason.

Quy D X Nguyen

11/27/2018, 4:18 AM

What's the right way to deserialize JSon into Kotlin data classes, accounting for nonnullability?

elect

11/27/2018, 8:46 AM

the whole

buildscript

section?

liminal

11/28/2018, 3:39 AM

how would i check if a float number has any non-zero decimal places 1f vs 1.2f

claudiug

11/28/2018, 11:21 AM

generate class is MainKt

Slackbot

11/28/2018, 11:31 AM

This message was deleted.

Narayan Iyer

11/28/2018, 4:44 PM

So, what's the problem here? I am used to head/tail in Scala, so I am writing my own head/tail:

fun <T> head(ls: List<T>): List<T> = ls.get(0)

error: type mismatch: inferred type is T but List<T> was expected
fun <T> head(ls: List<T>): List<T> = ls.get(0)
                                     ^

stephan_marshay

11/28/2018, 4:49 PM

val<T> List<T>.head: T 
   get()= this[0]

👍 2

Narayan Iyer

11/28/2018, 4:49 PM

So, when I write my tail function like so:

fun <T> tail(ls: List<T>): List<T> {
   return ls.drop(1)
}

why is it insisting on the

return

statement?!

stephan_marshay

11/28/2018, 4:50 PM

because you're declaring a return type (

List<T>

)

hudsonb

11/28/2018, 5:18 PM

run

needed there?

nekomatic

11/29/2018, 10:44 AM

Hi All, does any of you know of an elegant way to check for functions equality in Kotlin? I’m looking for a way to check if a function created with certain set of captured values can be verified as equal to same function created with a different but structurally equal set of captured values. Any Ideas?

tipsy

11/29/2018, 6:19 PM

currently i have

Pair(str.split(Regex(" "), 2)[0], str.split(Regex(" "), 2)[1])

, i could also use indeces.. is there a more elegant way?

dMusicb

11/29/2018, 6:40 PM

Does Kotlin have a way of letting you do something like:

for (i in (1..10)) {
    // do stuff
    someFunc() // inside someFunc call continue to skip below part
    // do other stuff
}

ursus

11/30/2018, 2:06 AM

what I meant is wether is there a way to alias it to void, i.e. no return value when that kotlin function is used in java

Slackbot

11/30/2018, 12:26 PM

This message was deleted.

febs

12/01/2018, 6:32 PM

About function literals. Both lambdas and anonymous functions are function literals according to the documentation https://kotlinlang.org/docs/reference/lambdas.html#instantiating-a-function-type I am wondering when anonymous functions should be used. I have seen plenty of uses of lambdas in code samples and tutorials but I still have to find some usage for an anonymous function. Where should I use one in place of a lambda, or simply, where should I just use one? Thanks ❤️

Title

febs

12/01/2018, 6:32 PM

hudsonb

12/01/2018, 6:45 PM

I think the only difference is in the

return

behavior

✔️ 1

karelpeeters

12/02/2018, 12:16 PM

I personally haven't found a use case for anonymous functions yet.

✔️ 1

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