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kotlinlang

Is it a bug  ?
```
interface GeoJson{
    val type:String
    val coordinates:Array&lt;*&gt;
    
    fun asPoint() = Point(coordinates as Array&lt;Double&gt;)
}
data class Point(val coordinates:Array&lt;Double&gt;)   

fun main(args: Array&lt;String&gt;) {        
    val json = """{"type":"Point", "coordinates":[1.0, 2.0]}"""  
    val obj = JSON.parse&lt;GeoJson&gt;(json).asPoint()        
    println("${obj.coordinates}")
}
```
<https://try.kotlinlang.org/#/UserProjects/2fobglofrrpnr9b0pru299uu31/6d1saqhqrbndev90djqurmuiv0>

I ran into the same problem. For this stuff to work properly use <https://github.com/Kotlin/kotlinx.serialization>

<@U3T6LDWTD> Yes, I changed the code and it works when using an extension function on the interface. Not with the member function. I think it’s a bug.
<@U94S6A9MM> at first I planned to use it. But there is also some limitations on the current version.

<@U0C1JH0RF> so, how was it look originally, what is a bug?

actually, deserialization from json to Kotlin class already somehow covered by kotlinx.serialization since 0.3, see  <https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/runtime_usage.md#dynamic-object-parser-js-only>

<@U0BMF6PDJ> I put the code back to the version that is not working. 
<https://try.kotlinlang.org/#/UserProjects/2fobglofrrpnr9b0pru299uu31/6d1saqhqrbndev90djqurmuiv0>

The main problem is that there is no error during compilation but at runtime it raises this error:
```
Unhandled JavaScript exception: 
TypeError: JSON.parse(...).asPoint is not a function
```

I tried to use kotlinx.serialization but it does not cover my use for the moment.

<https://kotlinlang.slack.com/archives/C7A1U5PTM/p1517869896000477?thread_ts=1517832345.000229&amp;cid=C7A1U5PTM>

I didn’t find yet the solution for my use case: deserialization of GeoJSON files (<https://tools.ietf.org/html/rfc7946>). I would like to have a performant multiplatform solution (which mean sharing class/interface). When we are calling `JSON.parse` we must use `external interfaces` that can’t be  in a common module. I must test the performance of deserialization with external interfaces, followed by a copy inside common classes. The problem is the size of GeoJSON files which can be big.

<@U0C1JH0RF> got it, thank you. Could you please crate an issue with your example. Ideally we must write some custom checks for JSON.parse.

about GeoJSON — if kotlinx.serialization (with custom serializations) doesn’t work for you, probably simplest and fastest (?) way is to parse the data to Map&lt;String, Any&gt; and write convertor from this map to your DTOs

<@U0BMF6PDJ> Done <https://youtrack.jetbrains.com/issue/KT-22784>

Thank you! Also let me know result of your tests.

“is to parse the data to Map&lt;String, Any&gt;“. What do you mean? Map is not an external interface. I can’t parse the text to it.
:thinking_face: