How to Build a Redux Pattern in SwiftUI

import SwiftUI

// MARK: - State

struct AppState {
    var count:     Int    = 0
    var isLoading: Bool   = false
    var message:   String = "Ready"
}

// MARK: - Actions

enum AppAction {
    case increment
    case decrement
    case reset
    case setMessage(String)
}

// MARK: - Reducer (pure function, no side-effects)

func appReducer(state: inout AppState, action: AppAction) {
    switch action {
    case .increment:
        state.count  += 1
        state.message = "Incremented to \(state.count)"

    case .decrement:
        state.count  -= 1
        state.message = "Decremented to \(state.count)"

    case .reset:
        state.count   = 0
        state.message = "Reset"

    case .setMessage(let msg):
        state.message = msg
    }
}

// MARK: - Store

@MainActor
final class Store<State, Action>: ObservableObject {
    @Published private(set) var state: State
    private let reducer: (inout State, Action) -> Void

    init(
        state: State,
        reducer: @escaping (inout State, Action) -> Void
    ) {
        self.state   = state
        self.reducer = reducer
    }

    func dispatch(_ action: Action) {
        reducer(&state, action)
    }
}

// MARK: - Root view — owns the store

struct ReduxRootView: View {
    @StateObject private var store = Store(
        state:   AppState(),
        reducer: appReducer
    )

    var body: some View {
        CounterView()
            .environmentObject(store)
    }
}

// MARK: - Child view — reads store from environment

struct CounterView: View {
    @EnvironmentObject private var store: Store<AppState, AppAction>

    var body: some View {
        VStack(spacing: 28) {
            Text(store.state.message)
                .font(.caption)
                .foregroundStyle(.secondary)
                .accessibilityLabel("Status: \(store.state.message)")

            Text("\(store.state.count)")
                .font(.system(size: 80, weight: .bold, design: .rounded))
                .contentTransition(.numericText())
                .accessibilityLabel("Count: \(store.state.count)")

            HStack(spacing: 24) {
                Button {
                    store.dispatch(.decrement)
                } label: {
                    Image(systemName: "minus.circle.fill")
                        .font(.largeTitle)
                }
                .accessibilityLabel("Decrement count")

                Button {
                    store.dispatch(.increment)
                } label: {
                    Image(systemName: "plus.circle.fill")
                        .font(.largeTitle)
                }
                .accessibilityLabel("Increment count")
            }
            .tint(.blue)

            Button("Reset") { store.dispatch(.reset) }
                .buttonStyle(.bordered)
                .accessibilityLabel("Reset count to zero")
        }
        .padding(32)
        .animation(.spring, value: store.state.count)
    }
}

#Preview {
    ReduxRootView()
}