Simplifying State by partially introducing unidirectional data flow in your codebase

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47. /// Model struct Cinnamon { let value: Int = 0

    } enum Event { case increase } 45

48. /// Model struct Cinnamon { let value: Int = 0

    } enum Event { case increase } func reducer(state: Cinnamon, event: Event) -> Cinnamon { var newState = state if event == .increase { newState.value += 1 } return newState } /// UI let builder = Form(state: Cinnamon(), reducer: reducer) 46

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52. struct AddressBook { var contacts: [Person] var searchTerm: String var

    scrollPosition: Int } 50

53. struct AddressBookApp { struct Data { var contacts: [Person] }

    var data: Data struct UI { var searchTerm: String var scrollPosition: Int } var ui: UI } 51

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68. private var subscribers: [String: (State)->Void] = [:] public func subscribe(_

    subscriber: @escaping (State)->Void) -> String { let token = UUID().uuidString subscribers[token] = subscriber subscriber(state) return token } 66

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70. protocol FormComponent { associatedtype State func setup(with state: State) func

    update(state: State) -> Void } public func subscribe<Component: FormComponent> (_ subscriber: Component) -> String where Component.State == State {... 68

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72. func subscribe<Type: Equatable>( path: KeyPath<Data, Type>, action: @escaping (_ oldValue:

    Type, _ newValue: Type) -> Void ) -> String struct Person { let name: String } form.subscribe(path: \Person.name) { (old, new) in ... } 70

73. private var history: [State] = [] func apply(_ change: (inout

    State) -> Void) { states.append(state) change(&state) notifySubscribers() } func undo() { state = history.popLast() notifySubscribers() } 71

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