Kontinuity

Effortless use of Kotlin Multiplatform coroutines in Swift, including suspend functions and Flow<T> returning members.

Installation

Kontinuity includes both a core Kotlin library, a Kotlin Symbol Processor, and various Swift Package Manager packages, depending on how you want to consume the generated code. Please make sure to use the same versions of each individual part.

Kotlin (Gradle)

In your Kotlin Multiplatform module, add the following to your build.gradle.kts file:

plugins {
    id("com.google.devtools.ksp")
}

kotlin {
    sourceSets {
        val commonMain by getting {
            dependencies {
                implementation("io.mockative:kontinuity-core:1.0.0-SNAPSHOT")
            }
        }
    }
}

dependencies {
    add("kspIos", "io.mockative:kontinuity-processor:1.0.0-SNAPSHOT")
}

Swift (Swift Package Manager)

The Swift libraries are available using Swift Package Manager (SPM), by adding the following to your Package.swift file, or in your Xcode Project's Package Dependencies.

dependencies: [
    .package(url: "https://github.com/mockative/Kontinuity.git", from: "<version>")
]

Usage

For each Kotlin class or interface annotated with @Kontinuity, a wrapper class is generated, referred to as the "Kontinuity Wrapper".

Given a Kotlin interface like the following:

package com.app.sample.tasks

@Kontinuity
interface TaskService {
    val tasks: StateFlow<List<Task>>

    suspend fun createTask(task: Task)

    fun close()
}

A Kontinuity Wrapper will be generated:

package com.app.sample.tasks

// The Kontinuity Wrapper class takes the prefix 'K' by default
open class KTaskService(private val wrapped: TaskService) {
    // Coroutine members have their names transformed with the 'K' suffix by default
    val tasksK: KontinuityStateFlow<Task>
        get() = wrapped.toKontinuityStateFlow()

    fun refreshK(): KontinuitySuspend<Unit> =
        kontinuitySuspend { wrapped.refresh() }

    // Simple members don't require a name transformation 
    fun close() =
        wrapped.close()
}

Swift

The generated Kontinuity Wrapper can be used in Swift through KontinuityCore and KontinuityCombine.

import KontinuityCore
import KontinuityCombine

val kotlinTaskService: TaskService
val taskService = KTaskService(wrapped: kotlinTaskService)

// Accessing the current value of a StateFlow
val tasks = getValue(of: taskService.tasksK)

// Subscribing to a Flow
val subscription = createPublisher(for: taskService.tasksK)
    .sink { completion in } receiveValue: { tasks in
        print("tasks: \(tasks)")
    } 

// Calling a suspend function
val subscription = createFuture(for: taskService.refreshK())
    .sink { completion in
        print("refresh: \(completion)")
    } receiveValue: { unit in }

Name Transformations

Kontinuity Wrapper classes have their names transformed from the type they're wrapping, by prefixing the class with K. Coroutine members of Kontinuity Wrapper classes also have their names transformed, in order to prevent the Kotlin compiler from suffixing it with _ when compiling for iOS/Darwin, which it does to prevent member signature clashes when interfaces are used.

See Configuration - Name Transformations for more information in how to configure Kontinuity.

Coroutine Scope

By default, Kontinuity launches all coroutines in a scope using Dispatchers.Main.immediate. You can override this behaviour by annotating a top-level property with @KontinuityScope. This annotation can both be applied to the entire source set (by specifying default = true), or to the @Kontinuity annotated types within a single source file:

// Specifies the coroutine scope used to launch Kontinuity coroutines of types within this source 
// set(s), unless otherwise overwritten by a file-level @KontinuityScope.
@SharedImmutable
@KontinuityScope(default = true)
internal val defaultKontinuityScope = CoroutineScope(Dispatchers.Default + SuperviserJob())

// Specifies the coroutine scope used to launch Kontinuity coroutines of types within this file.
@SharedImmutable
@KontinuityScope
internal val taskServiceScope = CoroutineScope(Dispatchers.Unconfined + SuperviserJob())

interface TaskService {
    // Coroutines launches within this type (and other types in this file) are launched in the 
    // `taskServiceScope`.
}

Roadmap

Add Swift mock library and generator
Add global @KontinuityScope annotation to control the default scope through a @SharedImmutable global variable.
Add type-local @KontinuityScope annotation to control the default scope on a per-type basis.
~~Consider rewriting SharedFlow<T> wrapper generation to generating 2 properties, one for the flow, one for the value %MValue.~~
- Implementing this breaks usage of suspend functions returning StateFlow<T>.

Credits

Kontinuity is heavily inspired by rickclephas/KMP-NativeCoroutines, and is essentially a Kotlin Symbol Processor version of that Kotlin Compiler Plugin, born out of a desire to have similar features while maintaining compatibility with KSP.

mockative / Kontinuity