Collection.md

Collection

Problem

By default, exporting a collection like List<Int> is not generating an easy-to-use object and is considered not exportable: Exported declaration uses non-exportable property type: List<Int>.

If you want to export the class anyway, the generated typescript looks like that:

class Example {
    constructor();
    readonly myList: kotlin.collections.List<number>;
}

As kotlin.collections.List<> is not exported to Typescript, you have to convert list to array and vice-versa. Even a simple forEach on this List will look complex enough, and may end up with duplicated tricks several times in the typescript source code.

Previously we were using this trick on the KMP side

@Suppress("NON_EXPORTABLE_TYPE")
@JsExport
public class CrossListHelper {
    @JsName("CreateListFromJSArray")
    public fun <T> CreateListFromJSArray(jsArray: Array<T>?): List<T>? {
        return if (jsArray == null || jsArray.isEmpty()) null else jsArray.toList()
    }
}

and using the helper on a lot of API points from Kotlin to Ts.

Solution

By annotating a class with KustomExport, we'll generate a wrapper for the class to provide a better API.

@KustomExport
class Example {
    val myList = listOf(1, 2, 3)
}

Generated typescript:

class Example {
    constructor();
    readonly myList: Array<number>;
}

Go back to README