/// CodingKeyのマッピングを動的に切り替える
protocol CodingKeyMapper {
    static var mapper: [String: S<Self>.CodingKeys] { get }
}
extension CodingKeyMapper {
    static var mapper: [String: S<Self>.CodingKeys] { return [:] }

    static func key(_ stringValue: String) -> S<Self>.CodingKeys? {
        return mapper[stringValue]
    }
    static func stringValue(_ key: S<Self>.CodingKeys) -> String {
        return mapper.first { $0.value == key }?.key ?? String(describing: key)
    }
}