在ELM 0.19解码中超过8个地图

Question

I have flags decoder with default values.

flagsDecoder : Decode.Decoder Params
flagsDecoder =
    Decode.map8 Params
        (Decode.field "field1" (Decode.string) |> (Decode.withDefault) "1")
        (Decode.field "field2" (Decode.string)   |> (Decode.withDefault) "2")
        (Decode.field "field3" (Decode.string)   |> (Decode.withDefault) "3")
        (Decode.field "field4" (Decode.string) |> (Decode.withDefault) "4)
        (Decode.field "field5" (Decode.string)  |> (Decode.withDefault) "5")
        (Decode.field "field6" (Decode.int) |> (Decode.withDefault) 6)
        (Decode.field "field7" (Decode.string)    |> (Decode.withDefault) "7")
        (Decode.field "field8" (Decode.string)   |> (Decode.withDefault) "8")

How can i add more fields? I have a JSON object with 10 fields.

Answer 1

I would recommend using andMap from elm-community/json-extra :

flagsDecoder : Decode.Decoder Params
flagsDecoder =
    Decode.succeed Params
        |> Decode.andMap (Decode.field "field1" (Decode.string) |> (Decode.withDefault) "1")
        |> Decode.andMap (Decode.field "field2" (Decode.string)   |> (Decode.withDefault) "2")
        |> Decode.andMap (Decode.field "field3" (Decode.string)   |> (Decode.withDefault) "3")
        |> Decode.andMap (Decode.field "field4" (Decode.string) |> (Decode.withDefault) "4")
        |> Decode.andMap (Decode.field "field5" (Decode.string)  |> (Decode.withDefault) "5")
        |> Decode.andMap (Decode.field "field6" (Decode.int) |> (Decode.withDefault) "6")
        |> Decode.andMap (Decode.field "field7" (Decode.string)    |> (Decode.withDefault) "7")
        |> Decode.andMap (Decode.field "field8" (Decode.string)   |> (Decode.withDefault) "8")

But there are also other options like elm-json-decode-pipeline and a new experimental API . andMap is really simple and straight-forward though, to use along with and to switch to from mapN if needed.