gist.swift

import ComposableArchitecture

struct Environment {}

// Account

struct AccountState: Equatable {
  var username: String?
}

enum AccountAction: Equatable {
  case login(username: String, password: String)
  case logout
}

let accountReducer = Reducer<AccountState, AccountAction, Environment> { state, action, environment in
  return .none
}

// Counter

struct CounterState: Equatable {
  var count = 0
}

enum CounterAction: Equatable {
  case increase
  case decrease
}

let counterReducer = Reducer<CounterState, CounterAction, Environment> { state, action, environment in
  return .none
}

// App

struct AppState: Equatable {
  var accountState = AccountState()
  var counterState = CounterState()
  // imagine there are many other substates here as well, one for every feature of the app
}

enum AppAction: Equatable {
  case accountAction(AccountAction)
  case counterAction(CounterAction)
}

let appReducer = Reducer<AppState, AppAction, Environment>.combine(
  accountReducer.pullback(
    state: \.accountState,
    action: /AppAction.accountAction,
    environment: { $0 }
  ),
  counterReducer.pullback(
    state: \.counterState,
    action: /AppAction.counterAction,
    environment: { $0 }
  )
)

// ViewController

class MyFeatureViewController {
  private let accountViewStore: ViewStore<AccountState, AccountAction>
  private let counterViewStore: ViewStore<CounterState, CounterAction>

  init(accountViewStore: ViewStore<AccountState, AccountAction>, counterViewStore: ViewStore<CounterState, CounterAction>) {
    self.accountViewStore = accountViewStore
    self.counterViewStore = counterViewStore
  }
}