typedef enum : NSInteger
{
    kImageSizeUnknown = 0,

    kImageSize75,
    kImageSize110,
    kImageSize170,
    kImageSize220,
    kImageSize300,
    kImageSize450,
    kImageSize720,
    kImageSize1080,

    /* Size aliases */
    kImageSizeThumbnail = kImageSize75,
    kImageSizeSmall     = kImageSize170,
    kImageSizeMedium    = kImageSize450,
    kImageSizeLarge     = kImageSize720,
    kImageSizeXLarge    = kImageSize1080

} GnImageSize;

enum GNImageSize:Int, CaseIterable{
    case thumbnail
    case sizeSmall

    func toGnImageSize() -> GnImageSize {
        switch self {
        case .thumbnail:
            return kImageSizeThumbnail
        case .sizeSmall:
            return kImageSizeSmall
        }
    }

    static func toGnImageSize(sizeType:GNImageSize) -> GnImageSize {
        switch sizeType {
        case .thumbnail:
            return kImageSizeThumbnail
        case .sizeSmall:
            return kImageSizeSmall
        }
    }

}

enum GNImageSize:Int, CaseIterable{
    case thumbnail = GnImageSize.kImageSizeThumbnail
    case sizeSmall = GnImageSize.kImageSizeSmall
}

Raw value for enum case must be a literal