Serialize Kotlin tuples as JSON arrays

[gaborkr]

A Kotlin Pair(firstValue, secondValue) can be represented in JSON as an array: [firstValue, secondValue]. A JSON array of two elements can be represented as a Kotlin Pair.
Jackson should support this for all tuple types.

Add a new flag to SerializationFeature and DeserializationFeature that enables this conversion (although it would make sense for this to be the default).

[cowtowncoder]

If it's Kotlin-specific, SerializationFeature and DeserializationFeature typically should not be added: these are for general purpose features (across all or at least multiple formats). Kotlin-specific features could be added by Kotlin module of course.

However, could this be instead configured using @JsonFormat(shape=Shape.ARRAY)?
This can be done at multiple levels, including per-property and per-type (assuming tuple type(s) exist(s) as JVM classes).
With Shape it is possible to choose one of JSON shapes, as well as NATURAL, which is the default that class uses in absence of any configuration (which may be different from explicit settings in specific cases).

I can't speak to actual implementation here, above is just suggestion on how API for the feature should work if it was to be implemented.

[gaborkr]

This does not need to be Kotlin specific, any language that has a tuple type could benefit from this.

@JsonFormat sounds reasonable.

Actually, the following works just fine:

data class PairTest(@JsonFormat(shape = JsonFormat.Shape.ARRAY) val myPair: Pair<Int, Int>)

val mapper = ObjectMapper().registerKotlinModule() val testPairAsArray = mapper.readValue<PairTest>(mapper.writeValueAsString(PairTest(Pair(1, 2))))

[gaborkr]

data class PairTest(@JsonFormat(shape = JsonFormat.Shape.ARRAY) val myPair: Pair<Int, Int>)

println(mapper.writeValueAsString(PairTest(Pair(1, 2))))

prints

{"myPair":[1,2]}