Using Kotlin Flow in Swift

Working with asynchronous flows from Kotlin Multiplatform as Combine Publishers in Swift

Photo by the author.

My team recently started developing components for our mobile applications using Kotlin Multiplatform Mobile with Jetpack Compose on Android and SwiftUI on iOS.

If you’re already familiar with Kotlin, you may know about the concept of coroutines in Kotlin that greatly simplifies threading and asynchronous programming in general. One of the key components of coroutines in Kotlin is the Flow<T> type, which is the interface all asynchronous flows in Kotlin implement. While Flow<T> is straightforward to consume in Android (and JVM targets in general), representing interfaces in Objective-C/Swift brings with it the limitations of protocols, including a lack of generic type parameters.

While exploring the limits of code sharing between Android and iOS, we faced the challenge of having to consume these asynchronous flows from Kotlin in Swift without inhibiting the ease of use in Android. During the investigation of solutions to the problem, we went through a couple of options that I will cover in this article.

TL;DR: Accommodate usage in Swift by introducing overloads for methods returning Flow<T>, which invokes callbacks while collecting the asynchronous flow in a dedicated…