# Kotlin Multiplatform iOS Data types mappings

**URL:** <https://discuss.kotlinlang.org/t/kotlin-multiplatform-ios-data-types-mappings/18609>\
**Category:** Multiplatform\
**Created:** [July 28, 2020, 3:18pm UTC](https://discuss.kotlinlang.org/t/kotlin-multiplatform-ios-data-types-mappings/18609 "2020-07-28T15:18:50Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![someKotlinuser](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@someKotlinuser](https://discuss.kotlinlang.org/u/someKotlinuser)\
**Post date:** [July 28, 2020, 3:18pm UTC](https://discuss.kotlinlang.org/t/kotlin-multiplatform-ios-data-types-mappings/18609/1 "2020-07-28T15:18:50Z")

</div>

I struggle to understand how does the mapping between Kotlin and iOS works in practice. According to the table available under [kotlin lang](https://kotlinlang.org/docs/tutorials/native/apple-framework.html) a Kotlin List maps to Swift Array.  
A Kotlin function which takes Double as an argument can be directly called from Swift with a Double value. But a Kotlin function which takes List cannot be called with Double array [Double] but requires a KotlinDouble array [KotlinDouble]. Why is it like this ? It it possible to somehow pass a Double array directly ?