UserDefaults property wrapper

UserDefaultsProperty.swift

import Foundation

internal protocol AnyOptional {
  var isNone: Bool { get }
}

extension Optional: AnyOptional {
  var isNone: Bool {
    switch self {
      case .none: return true
      case .some: return false
    }
  }
}

@propertyWrapper
internal final class UserDefaults<Wrapped> {

  private let identifier: String
  private let `default`: Wrapped
  internal init(_ identifier: String, `default`: Wrapped) {
    self.identifier = identifier
    self.default = `default`
  }

  internal var wrappedValue: Wrapped {
    get {
      return UserDefaults.standard.object(forKey: identifier) as? Wrapped ?? `default`
    }
    set {
      if (newValue as? AnyOptional)?.isNone ?? false {
        UserDefaults.standard.removeObject(forKey: identifier)
      } else {
        UserDefaults.standard.set(newValue, forKey: identifier)
      }
    }
  }
}