Is there a way to store Set<Calendar.Component>?

Question

I have a pretty old project on Swift that still uses NSCalendar.Unit, and it's pretty convenient because its rawValue is a UInt that can be stored in my Core Data database. I want to move to newer Swift APIs, so I have to use Set<Calendar.Component>, but it seems like Calendar.Component is just a Swift enum without a rawValue. I have found that it has a hashValue, but Apple does not recommend to save it, and also Calendar.Component does not conform to Encodable. So is there any way to store Set<Calendar.Component> in Core Data or am I stuck with old NSCalendar.Unit?

Answer 1

You can make Calendar.Component conform to RawRepresentable and hence have a rawValue and then store it as the RawValue. Or you can also make it conform to Codable and then store it as Data.

extension Calendar.Component: RawRepresentable {
    public var rawValue: Int {
        switch self {
        case .calendar:
            return 0
        case .day:
            return 1
        case .era:
            return 2
        case .hour:
            return 3
        case .minute:
            return 4
        case .month:
            return 5
        case .nanosecond:
            return 6
        case .quarter:
            return 7
        case .second:
            return 8
        case .timeZone:
            return 9
        case .weekday:
            return 10
        case .weekdayOrdinal:
            return 11
        case .weekOfMonth:
            return 12
        case .weekOfYear:
            return 13
        case .year:
            return 14
        case .yearForWeekOfYear:
            return 15
        }
    }

    public init?(rawValue: Int) {
        switch rawValue {
        case 0:
            self = .calendar
        case 1:
            self = .day
        case 2:
            self = .era
        case 3:
            self = .hour
        case 4:
            self = .minute
        case 5:
            self = .month
        case 6:
            self = .nanosecond
        case 7:
            self = .quarter
        case 8:
            self = .second
        case 9:
            self = .timeZone
        case 10:
            self = .weekday
        case 11:
            self = .weekdayOrdinal
        case 12:
            self = .weekOfMonth
        case 13:
            self = .weekOfYear
        case 14:
            self = .year
        case 15:
            self = .yearForWeekOfYear
        default:
            return nil
        }
    }
}

Codable conformance isn't necessary, RawRepresentable should be enough, but leaving it here as a reference.

extension Calendar.Component: Codable {
    enum DecodingError: Error {
        case unknownRawValue
    }

    /// Throwable initialiser that throws when an unknown `RawValue` is passed to it
    /// Necessary for `init(from decoder:)` to be able to delegate to a non-failable init
    init(value: Int) throws {
        guard let component = Calendar.Component(rawValue: value) else {
            throw DecodingError.unknownRawValue
        }
        self = component
    }

    public init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let rawValue = try container.decode(Int.self)
        try self.init(value: rawValue)
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(self.rawValue)
    }
}