Custom decoder functions for built-in types?

[sgrove]

Issue Labels

• has-reproduction
• feature
• docs
• blocking
• good first issue

So this might be a bit strange, but it would possibly be nice to be able to define custom decoders for combination of ObjectType.fieldName.

Consider the code below:

let timestampJson = Js.Json.decodeString(timestamp);

      let date =
        switch (timestampJson) {
        | Some(stamp) => Js.Date.fromString(stamp)
        | None => Js.Date.make()
        };

Basically, I know there is a timestamp of DateTime which is represented as Json.t (string). It'd be really nice to be able to annotate my client with additional decoder information so that I automatically get an option(Js.Date.t).

Something akin to this perhaps:

let customDecoders = [ObjectField("User", "createdAt", parseDate)];

Then it'd be fairly easy to annotate all the types/fields that are date times, and remove the need for conversions everywhere at usage sites.

[Gregoirevda]

This thread tries to solve the same problem in JS.

Easiest solution seems to be a link, like this one (written in reason or bindings to it)

[fakenickels]

This is interesting, but I feel like it's more https://github.com/mhallin/graphql_ppx related than reason-apollo