kotlinlang #announcements

reified generics looks interesting indeed, haven't needed it yet, but looking forward to using it in abstract classes. no more getTClass methods that needs to be implemented for every class that extends the abstract class

jan.rabe

12/20/2016, 2:14 PM

can you return concrete subclass objects using

() -> T

dalexander

12/20/2016, 2:16 PM

You should be able to, ie.

Copy code

fun <T> example(input: String, factory: (String) -> T) {
  return factory(input)
}

works.

👍 3

dalexander

12/20/2016, 2:17 PM

Oh, you may need to use <out T> depending on your needs.

jan.rabe

12/20/2016, 2:17 PM

the more you know thanks, going to look into it

nitrog42

12/20/2016, 3:44 PM

hey guys, I have a weird question, in java I can do that :

nitrog42

12/20/2016, 3:45 PM

@User uploaded a file: Untitled

Untitled.java

nitrog42

12/20/2016, 3:45 PM

which is valid (well it doesn't for me but it is working)

nitrog42

12/20/2016, 3:46 PM

in kotlin, the same code will give me a " Type RxBleDeviceMock! is inaccessible in this context due to: RxBleDeviceMock!", because RxBleDeviceMock is package visible

nitrog42

12/20/2016, 3:47 PM

is there any way to avoid this error in Kotlin (I'm using a lib and don't want to modify it if I can) ?

kirillrakhman

12/20/2016, 3:47 PM

the public java method is returning a package private type?

nitrog42

12/20/2016, 3:47 PM

yes

nitrog42

12/20/2016, 3:47 PM

https://github.com/Polidea/RxAndroidBle/blob/master/mockrxandroidble/src/main/java/com/polidea/rxandroidble/mockrxandroidble/RxBleDeviceMock.java

nitrog42

12/20/2016, 3:48 PM

Never saw that before but the sample java project I'm using don't have any issue

kirillrakhman

12/20/2016, 3:48 PM

that's really unfortunate

kirillrakhman

12/20/2016, 3:48 PM

you should send a PR to return the interface type instead

kirillrakhman

12/20/2016, 3:48 PM

as a workaround, you can write a java class that delegates the call and returns the interface type

nitrog42

12/20/2016, 3:48 PM

oh yeah not bad

kirillrakhman

12/20/2016, 3:49 PM

Copy code

public class Helper {
    public RxBleDevice ReturnMock(DeviceBuilder builder) {
        return builder.build();
    }
}

nitrog42

12/20/2016, 3:51 PM

this is a really cool hack actually 😄

kirillrakhman

12/20/2016, 3:52 PM

you can use this technique for a couple of issues with kotlin

kirillrakhman

12/20/2016, 3:52 PM

or to break the type system

kirillrakhman

12/20/2016, 3:53 PM

nevertheless, this should be fixed on kotlin's side. I'll create an issue

kirillrakhman

12/20/2016, 3:57 PM

https://youtrack.jetbrains.com/issue/KT-15347

Dalinar

12/20/2016, 7:04 PM

how can I implement array access for my class? for instance I use

parameters["expiry"]

on a

HashMap<String,String>

java object. I replaced this

HashMap

with my own

Parameters

class... now what should I do? Implement the

Map

Interface ? is that how I can achieve array access for the

Parameters

class ?

dalexander

12/20/2016, 7:05 PM

https://kotlinlang.org/docs/reference/operator-overloading.html overriding

get()

and

set()

should let you do that.

Dalinar

12/20/2016, 7:05 PM

thanks I'll read up on it

12/20/2016, 7:40 PM

Has anyone written a tensor contraction before? I'm trying to think of the best way to do it in Kotlin.

12/20/2016, 7:41 PM

I need to iterate over all the values of all the indices of the outer tensor (less the last), and all the values of all the indices of the inner tensor (less the first).

12/20/2016, 7:41 PM

I can do it the "stupid way".