OneWay

OneWay is a simple and lightweight library for state management with unidirectional data flow. It is fully supported for using anywhere that uses Swift. You can use it on any platform and with any framework. There are no dependencies on third parties, so you can use OneWay purely. It can not only be used in the presentation layer, but can also be used to simplify complex business logic. It will be useful whenever you want to design logic in unidirection.

Data Flow

Usage

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(
                .just(.increment),
                .just(.increment)
            )
        }
    }

}

Sending Actions

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

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

way.send(.increment)
way.send(.decrement)
way.send(.twice)

print(way.state.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

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

way.publisher.map(\.number)
    .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 CounterWay: Way<CounterWay.Action, CounterWay.State> {
// ...
    override func bind() -> SideWay<Action, Never> {
        return .merge(
            globalTextSubject
                .map({ Action.saveText($0) })
                .eraseToSideWay(),
            globalNumberSubject
                .map({ Action.saveNumber($0) })
                .eraseToSideWay()
        )
    }
// ...
}

Catching Errors

There are several functions that handle errors. It is a little easier to understand if you refer to unit tests.

override func reduce(state: inout State, action: Action) -> SideWay<Action, Never> {
    switch action {
    // ...
    case .fetchDataWithError:
        return fetchData()
            .map({ Action.dataDidLoad($0) })
            .catch({ Action.handleError($0) })
            .eraseToSideWay()
    case .fetchDataWithJustReturn:
        return fetchData()
            .map({ Action.dataDidLoad($0) })
            .catchToReturn(Action.failToLoad)
            .eraseToSideWay()
    case .fetchDataWithIgnoringErrors:
        return fetchData()
            .map({ Action.dataDidLoad($0) })
            .catchToNever()
            .eraseToSideWay()
    // ...
    }
}

Swift Concurrency

async/await can also be used with Way.

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

    enum Action {
        case fetchNumber
        case setNumber(Int)
    }

    struct State: Equatable {
        var number: Int
    }

    override func reduce(state: inout State, action: Action) -> SideWay<Action, Never> {
        switch action {
        case .fetchNumber:
            return .async {
                let number = await fetchNumber()
                return Action.setNumber(number)
            }
        case .setNumber(let number):
            state.number = number
            return .none
        }
    }

}

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 CounterWay: NSWay<CounterWay.Action, CounterWay.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 = CounterWay(initialState: initialState, threadOption: .current)
let threadSafeWay = CounterWay(initialState: initialState, threadOption: .threadSafe)

Documentation

Learn how to use OneWay by going through the documentation created using DocC.

Benchmark

Compared to other libraries, OneWay shows very good performance.

For more details, 👉 OneWayBenchmark

Lower is better

Examples

OneWayExample
- UIKit
- SwiftUI

Requirements

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

Installation

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: "1.0.0"),
]

Next Step

Testing queue for asynchronous test case.
Debugging tool that can log all actions and states.

References

These are the references that inspired OneWay a lot.

License

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

1.3.0

What's New