Hi Arsen,
What’s the difference between providing a method that takes a transformable
object on the keyed container protocol and just transforming it yourself before
you encode it?
- Tony
> On Dec 18, 2017, at 8:51 AM, Arsen Gasparyan via swift-evolution
> <swift-evolution@swift.org> wrote:
>
> Hello everyone,
>
> I’m suggesting to add a new way to encode/decode JSON properties for
> relevantly complex data formats such as regular expressions, well-known text,
> hex colours, custom date formats.
>
> The problem:
>
> Image you have a struct called House
>
> struct House {
> let color: UIColor
> }
>
> and it has a properly called color and the color represented in JSON as hex
> value (#ffffff). Currently to make it working you have to extract the
> underline value (string with a hex value) and then try to make a UIColor from
> it. It works but it makes you to copy/past a lot of code and it leads to
> problems. Also it shifts focus from what to decode to how to decode.
>
> The suggested solution:
>
> I suggest that we have to introduce protocols for classes that will
> encapsulate transformation from a source data type to a destination data
> type. The source data types are all existing data that support of decoding.
>
> We will provide only protocols (one for decoding and one for encoding) and
> users will be able to create transformers for their own data types.
>
> The implementation:
>
> The implementation is fairly easy. We only need introduce two protocols
> (encoding/decoding) and add a method to KeyedEncodingContainerProtocol that
> will accept a key and a transformer. In the method we will extract source
> data from JSON and then will ask the transformer to try to convert it to the
> desire data type.
>
> Example of the decoding protocol:
>
> protocol DecodingTransformer {
> associatedtype Input: Decodable
> associatedtype Output
> func transform(_ decoded: Input) throws -> Output
> }
>
>
> Inspired by: https://github.com/Hearst-DD/ObjectMapper#custom-transforms
> <https://github.com/Hearst-DD/ObjectMapper#custom-transforms>
>
> Cheers,
> Arsen
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