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DevYeom/OneWay 0.5.0
A Swift library for state management with unidirectional data flow.
⭐️ 14
🕓 5 days ago
iOS macOS watchOS tvOS
.package(url: "https://github.com/DevYeom/OneWay.git", from: "0.5.0")


Swift release Platforms CI license

OneWay is a super simple and lightweight library for state management with unidirectional data flow. The original inspiration came from Flux, The Composable Architecture, ReactorKit and many state management libraries. It's easy to learn and use. There are no dependencies on third parties, so you can use OneWay purely. It can not only be used in the presentation layer (e.g. with View or ViewController), but can also be used to simplify complex business logic (e.g. while the app launches). The basic concept is to think of each way separately.

Data Flow



Implementing a Way

It is easy to think of a Way as a path through which data passes. You can inherit a Way and should implement as below. It is also freely customizable and encapsulatable, since Way is a class.

final class CounterWay: Way<CounterWay.Action, CounterWay.State> {

    enum Action {
        case increment
        case decrement
        case twice

    struct State: Equatable {
        var number: Int

    override func reduce(state: inout State, action: Action) -> SideWay<Action, Never> {
        switch action {
        case .increment:
            state.number += 1
            return .none
        case .decrement:
            state.number -= 1
            return .none
        case .twice:
            return .concat(

Sending Actions

Sending an action to a Way causes changes in the state via reduce().

let way = CounterWay(initialState: .init(number: 0))


print(way.currentState.number) // 2

Subscribing a Way

When a value changes, it can receive a new value. It guarantees that the same value does not come down consecutively. In general, you don't need to add removeDuplicates(). But if you want to receive all values when the way's state changes, use map operator to way's publisher.

// number <- 10, 10, 20 ,20

    .sink { number in
        print(number) // 10, 20
    .store(in: &cancellables)

    .sink { number in
        print(number) // 10, 10, 20, 20
    .store(in: &cancellables)

Global States

You can easily subscribe to global states by overriding bind().

let globalTextSubject = PassthroughSubject<String, Never>()
let globalNumberSubject = PassthroughSubject<Int, Never>()

final class CustomWay: Way<CustomWay.Action, CustomWay.State> {
// ...
    override func bind() -> SideWay<Action, Never> {
        return .merge(
                .map({ Action.saveText($0) })
                .map({ Action.saveNumber($0) })
// ...

Supporting NSObject

Way is a class, not a protocol. Therefore, multiple inheritance is not possible. There are often situations where you have to inherit NSObject. NSWay was added for this occasion. In this case, inherit and implement NSWay, and in other cases, inherit Way.

final class TestWay: NSWay<TestWay.Action, TestWay.State> {
    // ...

Thread Safe or Not

Way has a ThreadOption to consider the multithreaded environment. This option can be passed as an argument to the initializer. Once set, it cannot be changed. In a general environment, it is better to use the default option(current) for better performance. But, if it is initialized with the current option, all interactions (i.e. sending actions) with an instance of Way must be done on the same thread.

let way = TestWay(initialState: initialState, threadOption: .current)
let threadSafeWay = TestWay(initialState: initialState, threadOption: .threadSafe)


Compared to other libraries, OneWay shows very good performance. In particular, the usage is very similar to ReactorKit, so it is easy to use, but it is about 10 times faster.

For more details, 👉 OneWayBenchmark

Lower is better

Benchmark1 Benchmark2



Minimum Version
Swift 5.5
Xcode 13.0
iOS 13.0
macOS 10.15
tvOS 13.0
watchOS 6.0


OneWay is only supported by Swift Package Manager.

To integrate OneWay into your Xcode project using Swift Package Manager, add it to the dependencies value of your Package.swift:

dependencies: [
  .package(url: "https://github.com/DevYeom/OneWay", from: "0.1.0"),


This library is released under the MIT license. See LICENSE for details.


Stars: 14
Last commit: 6 days ago
jonrohan Something's broken? Yell at me @ptrpavlik. Praise and feedback (and money) is also welcome.

Release Notes

6 days ago


  • A reset() function
    • Reset some properties and subscriptions. This is useful when you need to call bind() again.
  • Benchmark and examples in README.md

Swiftpack is being maintained by Petr Pavlik | @ptrpavlik | @swiftpackco | API | Analytics