TCA Inputs Outputs

example.swift

struct SomeFeature: ReducerProtocol {
    struct State: Equatable {}
    enum Action: Equatable {
        case didAppear
        case refreshData
        case didComplete
    }
    
    struct Input {
        var shouldRefresh: () -> AsyncStream<Void>
    }
    
    struct Output {
        var didCompleteFlow: () -> Void
    }
    
    /// Allows plugging in events from the outside world
    /// that can trigger a certain behaviour within this feature.
    public let input: Input?
    
    /// Allows notifying the outside world of certain events
    /// that have happened within this feature
    public let output: Output?
    
    var body: some ReducerProtocol<State, Action> {
        Reduce { state, action in
            switch action {
            case .didAppear:
                guard let input else { return .none }
                return .run { send in
                    for await _ in input.shouldRefresh() {
                        // Forward outside world event into
                        // our current domain
                        await send(.refreshData)
                    }
                }
                
            case .refreshData:
                // do some work
                return .none
                
            case .didComplete:
                return .fireAndForget {
                    // let the outside world know the
                    // user did complete the flow
                    output?.didCompleteFlow()
                }
            }
        }
    }
}

// USAGE:
func createScreen(
    someImportantEventStream: AnyPublisher<Void, Never>,
    onFlowCompletion: @escaping () -> Void
) {
    let input = SomeFeature.Input {
        AsyncStream(someImportantEventStream.values)
    }
    let output = SomeFeature.Output(didCompleteFlow: onFlowCompletion)
    
    let store = Store(
        initialState: SomeFeature.State(),
        reducer: SomeFeature(
            input: input,
            output: output
        )
    )
    
    let view = ...
}