@objc(TTCategoryBase)
class TTCategoryBase: NSManagedObject {
    /// Backing of the category type.
    @NSManaged fileprivate var categoryTypeRaw: String
}

/// Category middle-class with generics.
class TTCategory<T: RawRepresentable>: TTCategoryBase where T.RawValue == String {
    /// Category type.
    var categoryType: T {
        return T.init(rawValue: self.categoryTypeRaw)!
    }
}

@objc(TTMessageCategory)
final class TTMessageCategory: TTCategory<TTMessageCategory.CategoryType> {
    enum CategoryType: String {
        case news
        case programmeChanges = "programme_changes"
    }
}