Hi I m trying to make the last line work ```fun lt T gt gena

Question

Hi I m trying to make the last line work ```fun lt T gt genattrs vararg args T ArrayList lt T gt val arrays = ArrayList lt T gt arrays addAll args return arrays val f = lt Int gt genattrs invalid syntax ```

enleur · Answer

Shawn · Answer

< robinchew> try `val f Array lt out Int gt gt ArrayList lt Int gt = genattrs`

robinchew · Answer

Thanks < enleur> Hey again < Shawn> looks like a simillar issue I had before

Shawn · Answer

those pesky function types lol

robinchew · Answer

Hmmmm why Array instead of ArrayList

Shawn · Answer

that s what `vararg params T` is sugar for `Array lt out T gt `

Shawn · Answer

having a function type like ` vararg Int gt ` isn t supported

Shawn · Answer

not sure if it ever will but ツ

robinchew · Answer

man I would never have figured that

robinchew · Answer

You work at jetbrains designing kotlin or something

Shawn · Answer

nah I m just partial to reading the docs stuck out tongue <https kotlinlang org docs reference functions html variable number of arguments varargs>

robinchew · Answer

I guess I don t read docs

Shawn · Answer

lol I m just ribbing you it s no biggie

robinchew · Answer

google copy paste programming

Shawn · Answer

docs aren t always that helpful until you ve got a bit of familiarity with the thing documented anyhow

robinchew · Answer

Hmm i think im still getting issues

Shawn · Answer

story of my life lol

robinchew · Answer

The following ``` val attrs Array lt out Int gt gt ArrayList lt Int gt = genattrs ``` Is not the same as ``` fun attrs vararg args Int ArrayList lt Int gt val arrays = ArrayList lt Int gt arrays addAll args return arrays ```

robinchew · Answer

I will get the red squiggly underline when trying to use `attrs 1 2 3 `

Shawn · Answer

well I m a little unclear as to what the error is exactly but I feel like oughta point out that if the function needs to take one type and return another the signature needs more than one type parameter

Shawn · Answer

so if you re trying to go from `Virtual ` to `Int` you need a function like

Shawn · Answer

``` fun lt T R gt genAttrs vararg args T ArrayList lt R gt ```

robinchew · Answer

sorry i keep making mistakes

robinchew · Answer

I meant to replace Virtual with Int

Shawn · Answer

gotcha

Shawn · Answer

I see what you mean

Shawn · Answer

yeah unfortunately you can t really have vararg lambda params confused

Shawn · Answer

I d bet money there s a youtrack to vote for that concerns it

robinchew · Answer

Even this has issues ``` fun attrs vararg args Int ArrayList lt Int gt val arrays = ArrayList lt Int gt arrays addAll args return arrays ``` apparently `varargs args Int` is a `collection lt Int gt ` type which is not the same as `ArrayList lt Int gt `

robinchew · Answer

So I gotta do ``` fun attrs vararg args Int ArrayList lt Int gt val arrays = ArrayList lt Int gt arrays addAll args as ArrayList lt Int gt return arrays ```

Shawn · Answer

ah so this is another Kotlin gotcha unfortunately

Shawn · Answer

there are optimized arrays for primitive types or maybe just the primitive numeric types I oughta read up on that

Shawn · Answer

so instead of args presenting in the function as `Array lt Int gt ` it s `IntArray` which has a different inheritance hierarchy

robinchew · Answer

right so back to the ` genAttrs` problem I guess this doesn t work

Shawn · Answer

if your goal is to take save a reference to a varargs fun such that you can use the reference to call it using varargs then no I don t think it ll work

robinchew · Answer

Oh well Is there an equivalent of ```arrayListOf 1 2 3 ``` but expecting 1 array argument instead something like ``` NewArrayList arrayListOf 1 2 3 ```

Shawn · Answer

Oh are you just trying to make a deep copy of an existing arraylist

Shawn · Answer

or rather not a deep copy but just a copy of an arraylist instead of just another reference

robinchew · Answer

Actually I basically want to give `arrayListOf` an alternate name so I can just do `a 1 2 3 ` instead of `arrayListOf 1 2 3 `

Shawn · Answer

oh

robinchew · Answer

Doing `a = arrayListOf` dont work

Shawn · Answer

for that you re just gonna have to define a new function I guess

Shawn · Answer

``` fun lt T gt a vararg args T ArrayList lt T gt = arrayListOf args ```

Shawn · Answer

I d also suggest using a type higher up the chain than `ArrayList` if you can help it

Shawn · Answer

`List` if you can do with a read only interface `MutableList` if you need those add remove methods

robinchew · Answer

I thought ` ` wasn t supported which is like ` ` right

Shawn · Answer

well ` ` means a couple different things depending on the language lol but ` ` is definitely supported as the array spread operator

Shawn · Answer

lets you pass in arrays where you need varargs

robinchew · Answer

Damn the syntax is weird a function declaration with `=` instead of ` `

Shawn · Answer

lol you don t need the expression body syntax here but I like it for one liners

robinchew · Answer

foreign but good to know

Shawn · Answer

cribbed from scala iirc

Shawn · Answer

you can even omit the return type when you use expression bodies but that s bad juju for public API methods and instances where the return type is ambiguous or unintuitive

robinchew · Answer

Now what about a short function for a data class

Shawn · Answer

going to need to be a bit more specific lol

robinchew · Answer

Say I got ``` data class GlobalState val age Int = 0 val count Int = 0 val selectedIndex String = invalid key ``` When instantiating that I just want to do ```GS 1 1 key ```

robinchew · Answer

Just renaming GlobalState is an obvious answer

Shawn · Answer

I don t really get your proclivity towards shortening names but in this case you can just use a `typealias`

Shawn · Answer

``` typealias GS = GlobalState elsewhere val gs = GS 1 1 key ```

robinchew · Answer

Just providing choices

robinchew · Answer

If you must know I m building an equivalent of this <https mithril js org dom elements>

Shawn · Answer

didn t you say you were coming from a Python background aren t you folks all about following the BDFL and there being only one way to do something stuck out tongue

Shawn · Answer

granted Guido did abdicate a little while back so I m not sure where everyone stands on that one lol

robinchew · Answer

Oh I got a JavaScript background too I m out of control

Shawn · Answer

wild lol

robinchew · Answer

``` m LinearLayout attrs size 400 WRAP backgroundColorHex 009999 elevation 1f margin 50 children m TextView arrayListOf onCrup movingView gt value animation setView movingView parent as LinearLayout size WRAP MATCH weight 1f layoutGravity CENTER VERTICAL padding 5 text $ value name $ selectedTop $ value checked backgroundColorHex 000066 onTouch v motionEvent gt val view = v parent as LinearLayout ```

Shawn · Answer

oof

Shawn · Answer

this looks like something much better expressed using a DSL

robinchew · Answer

No need to learn another language

Shawn · Answer

no I mean like you can use Kotlin to mimic a DSL

Shawn · Answer

see kotlin gradle build scripts or < C0BRKJ9K9|kobalt> for example

Shawn · Answer

or even the kotlinx html example

Shawn · Answer

you could build something that maybe more resembles this

Shawn · Answer

``` m LinearLayout attrs size 400 WRAP backgroundColorHex = 009999 elevation = 1f margin = 50 children +TextView onCrup movingView gt value animation setView movingView parent as LinearLayout size WRAP MATCH weight = 1f layoutGravity = CENTER VERTICAL padding = 5 text = $ value name $ selectedTop $ value checked backgroundColorHex = 000066 onTouch v motionEvent gt view = v parent as LinearLayout ```

robinchew · Answer

Thanks for that At this point though it s not worth adding more code just to get rid of those commas and brackets