RxFeedback

The simplest architecture for RxSwift

    typealias Feedback<State, Event> = (Observable<State>) -> Observable<Event>

    public static func system<State, Event>(
        initialState: State,
        reduce: @escaping (State, Event) -> State,
        feedback: Feedback<State, Event>...
    ) -> Observable<State>

Why

• Straightforward

  • If it did happen -> Event
  • If it should happen -> Request
  • To fulfill Request -> Feedback loop

• Declarative

  • System behavior is first declaratively specified and effects begin after subscribe is called => Compile time proof there are no “unhandled states”

• Debugging is easier

  • A lot of logic is just normal pure function that can be debugged using Xcode debugger, or just printing the commands.

• Can be applied on any level

  • Entire system
  • application (state is stored inside a database, CoreData, Firebase, Realm)
  • view controller (state is stored inside system operator)
  • inside feedback loop (another system operator inside feedback loop)

• Works awesome with dependency injection

• Testing

  • Reducer is a pure function, just call it and assert results
  • In case effects are being tested -> TestScheduler

• Can model circular dependencies

• Completely separates business logic from effects (Rx).

  • Business logic can be transpiled between platforms (ShiftJS, C++, J2ObjC)

Examples

Simple UI Feedback loop

Complete example

 Observable.system(
    initialState: 0,
    reduce: { (state, event) -> State in
        switch event {
        case .increment:
            return state + 1
        case .decrement:
            return state - 1
        }
    },
    scheduler: MainScheduler.instance,
    feedback:
        // UI is user feedback
        bind(self) { me, state -> Bindings<Event> in
            let subscriptions = [
                state.map(String.init).bind(to: me.label.rx.text)
            ]

            let events = [
                me.plus.rx.tap.map { Event.increment },
                me.minus.rx.tap.map { Event.decrement }
            ]

            return Bindings(
                subscriptions: subscriptions,
                events: events
            )
        }
)

Play Catch

Simple automatic feedback loop.

Complete example

Observable.system(
    initialState: State.humanHasIt,
    reduce: { (state: State, event: Event) -> State in
        switch event {
        case .throwToMachine:
            return .machineHasIt
        case .throwToHuman:
            return .humanHasIt
        }
    },
    scheduler: MainScheduler.instance,
    feedback:
        // UI is human feedback
        bindUI,
        // NoUI, machine feedback
        react(request: { $0.machinePitching }, effects: { (_) -> Observable<Event> in
            return Observable<Int>
                .timer(1.0, scheduler: MainScheduler.instance)
                .map { _ in Event.throwToHuman }
        })
)

Paging

Complete example

Driver.system(
    initialState: State.empty,
    reduce: State.reduce,
    feedback:
        // UI, user feedback
        bindUI,
        // NoUI, automatic feedback
        react(request: { $0.loadNextPage }, effects: { resource in
            return URLSession.shared.loadRepositories(resource: resource)
                .asSignal(onErrorJustReturn: .failure(.offline))
                .map(Event.response)
        })
)

Run RxFeedback.xcodeproj > Example to find out more.

Installation

CocoaPods

CocoaPods is a dependency manager for Cocoa projects. You can install it with the following command:

$ gem install cocoapods

To integrate RxFeedback into your Xcode project using CocoaPods, specify it in your Podfile:

pod 'RxFeedback', '~> 3.0'

Then, run the following command:

$ pod install

Carthage

Carthage is a decentralized dependency manager that builds your dependencies and provides you with binary frameworks.

You can install Carthage with Homebrew using the following command:

$ brew update
$ brew install carthage

To integrate RxFeedback into your Xcode project using Carthage, specify it in your Cartfile:

github "NoTests/RxFeedback" ~> 3.0

Run carthage update to build the framework and drag the built RxFeedback.framework into your Xcode project. As RxFeedback depends on RxSwift and RxCocoa you need to drag the RxSwift.framework and RxCocoa.framework into your Xcode project as well.

Swift Package Manager

The Swift Package Manager is a tool for automating the distribution of Swift code and is integrated into the swift compiler.

Once you have your Swift package set up, adding RxFeedback as a dependency is as easy as adding it to the dependencies value of your Package.swift.

dependencies: [
    .package(url: "https://github.com/NoTests/RxFeedback.swift.git", majorVersion: 1)
]

Difference from other architectures

• Elm - pretty close, feedback loops for effects instead of Cmd, which effects to perform are encoded into state and queried by feedback loops
• Redux - kind of like this, but feedback loops instead of middleware
• Redux-Observable - observables observe state vs. being inside middleware between view and state
• Cycle.js - no simple explanation 😃, ask @andrestaltz
• MVVM - separates state from effects and doesn’t require a view