Which Implementation is Better?

[DeokHo98]

@Reducer
struct Feature1 {
    @ObservableState
    struct State: Equatable {
        var currentMonth: Date = Date()
        var selectedDate: Date?

        var navigationTitle: String {
            let formatter = DateFormatter()
            formatter.dateFormat = "yyyy년 MM월"
            return formatter.string(from: currentMonth)
        }

        var addButtonIsHidden: Bool {
            selectedDate == nil ? true : false
        }
    }

    enum Action {
        case todayButtonTap
        case changeMonth(Date)
        case dateButtonTap(Date)
    }

    var body: some ReducerOf<Self> {
        Reduce { state, action in
            switch action {
            case .todayButtonTap:
                state.currentMonth = Date()
                state.selectedDate = nil
            case .changeMonth(let date):
                state.currentMonth = date
                state.selectedDate = nil
            case .dateButtonTap(let date):
                state.selectedDate = date
            }
            return .none
        }
    }
}

Feature1 calculates navigationTitle and addButtonIsHidden dynamically using computed properties in the State struct.

@Reducer
struct Feature2 {
    @ObservableState
    struct State: Equatable {
        var currentMonth: Date = Date()
        var selectedDate: Date?
        var navigationTitle: String = ""
        var addButtonIsHidden: Bool = ""
    }

    enum Action {
        case todayButtonTap
        case changeMonth(Date)
        case dateButtonTap(Date)
    }

    var body: some ReducerOf<Self> {
        Reduce { state, action in
            switch action {
            case .todayButtonTap:
                state.currentMonth = Date()
                state.selectedDate = nil
                state.navigationTitle = self.navigationTitle(currentMonth: state.currentMonth)
                state.addButtonIsHidden = self.addButtonIsHidden(selectedDate: state.selectedDate)
            case .changeMonth(let date):
                state.currentMonth = date
                state.selectedDate = nil
                state.navigationTitle = self.navigationTitle(currentMonth: state.currentMonth)
                state.addButtonIsHidden = self.addButtonIsHidden(selectedDate: state.selectedDate)
            case .dateButtonTap(let date):
                state.selectedDate = date
                state.addButtonIsHidden = self.addButtonIsHidden(selectedDate: state.selectedDate)
            }
            return .none
        }
    }

    private func navigationTitle(currentMonth: Date) -> String {
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy년 MM월"
        return formatter.string(from: currentMonth)
    }

    private func addButtonIsHidden(selectedDate: Date?) -> Bool {
        selectedDate == nil ? true : false
    }
}

Feature2 updates these properties explicitly within the reducer actions.
Which approach is more efficient and maintainable, and what are the potential benefits and drawbacks of each?

[Alex293]

You can reduce your example to simply properties vs computed properties. Computed properties have obvious advantages for maintainability, you have a single place where you have the logic but if it's quite expensive to read, often read and rarely written it might be more efficient to use the second approach. I'd say default to the first one.

[DeokHo98]

Thank you!