Sample Property Wrappers

PropertyWrappers.swift

@propertyWrapper
/// Wrapper used to easily encode a `Date` to and decode a `Date` from an ISO 8601 formatted date string.
struct ISO8601Date: Codable {
    var wrappedValue: Date
    
    init(wrappedValue: Date) {
        self.wrappedValue = wrappedValue
    }
    
    init(from decoder: Decoder) throws {
        let value = try decoder.singleValueContainer()
        let stringValue = try value.decode(String.self)
        if let date = ISO8601DateFormatter().date(from: stringValue) {
            wrappedValue = date
        } else {
            throw DecodingError.typeMismatch(Date.self, DecodingError.Context(codingPath: [], debugDescription: "Failed to decode ISO Date. Invalid string format."))
        }
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        
        let string = ISO8601DateFormatter().string(from: wrappedValue)
        try container.encode(string)
    }
}

struct DateTest: Codable {
    @ISO8601Date var date: Date = Date()
}

@propertyWrapper
struct UserDefault<StoredType> {
    public let key: String
    public let defaultValue: StoredType

    var wrappedValue: StoredType {
        get {
            UserDefaults.standard.object(forKey: key) as? StoredType ?? defaultValue
        }
        set {
            UserDefaults.standard.set(newValue, forKey: key)
        }
    }
}

class SettingManager {
    @UserDefault(key: "userViewedWhatsNew", defaultValue: false) static var userViewedWhatsNew: Bool
    
    @UserDefault(key: "lastLoggedInUser", defaultValue: nil) static var lastLoggedInUser: String?
}