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Add emptyObject #23

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b89d081
Add emptyObject
Janiczek Feb 6, 2019
c8d5970
Remove unneeded import
Janiczek Feb 6, 2019
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28 changes: 26 additions & 2 deletions src/Json/Decode/Extra.elm
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ module Json.Decode.Extra exposing
, when
, collection, sequence, combine, indexedList, keys
, set
, dict2
, dict2, emptyObject
, withDefault, optionalField
, fromResult
, parseInt, parseFloat, doubleEncoded
Expand Down Expand Up @@ -40,7 +40,7 @@ module Json.Decode.Extra exposing

# Dict

@docs dict2
@docs dict2, emptyObject


# Maybe
Expand Down Expand Up @@ -165,6 +165,30 @@ decodeDictFromTuples keyDecoder tuples =
fail (errorToString error)


{-| Succeed only when given an empty JSON object (`{}`).

import Json.Decode exposing (..)

decodeString emptyObject "{}"
--> Ok ()

Anything else makes the decoder fail.

-}
emptyObject : Decoder ()
emptyObject =
keyValuePairs (succeed ())
|> andThen
(\pairs ->
case pairs of
[] ->
succeed ()

_ ->
fail "Expecting an empty object"
)


{-| Try running the given decoder; if that fails, then succeed with the given
fallback value.

Expand Down