Support Responses of Type unit

[SCullman]

For example, I usually return just the response code on DELETE requests.
Fetch.delete<Data,unit> fails because there is no Auto decoder for unit.

Same for PATCH,POST and PUT. It might even make sense for GET, if the request just triggers a side effect, is used as RPC.

Proposals

• Either adding an Auto decoder for unit in Thoth.Json
• or handling here in Thoth.Fetch

[MangelMaxime]

We should support it in Thoth.Json(.Net)

The question is how should be represents unit in JSON?

[SCullman]

As a workaround, I add the following ExtraCoder:

module Extra =
    let unitDecoder : Decoder<unit> =fun _ _ -> () |> Ok
    let unitEncoder () :  JsonValue = failwith "Cannot encode unit"
    let unit extra = 
        Extra.withCustom unitEncoder unitDecoder  (defaultArg extra Extra.empty) |> Some

Then I pass ?extra = Extra.unit extra to all my calls of Thoth.Fetch.

[SCullman]

My proposed Decode/Encoder doesn't work.
line 44

            let! body = response.text()
            return Decode.unsafeFromString decoder body

body is an empty string, and Decode.unsafeFromString fails with Uncaught SyntaxError: Unexpected identifier

[SCullman]

My temporary fix:

            let! body = response.text()
            let result = if body = ""
                         then unbox ()
                         else Decode.unsafeFromString decoder body
            return result

Same for tryFetchAs. The ExtraCoder (which is never called) is still needed.

[SCullman]

@MangelMaxime
You were right to fix it int Thoth.Json. Fix is in thoth-org/Thoth.Json#25

[SCullman]

And similar fix added also to Thoth.Json.Net.