Why can't I do fromJson to a List[Any]? about spray-json

[NicholasSterling]

Same question for toJson:

scala> List(1,"two").toJson
:14: error: Cannot find JsonWriter or JsonFormat type class for List[Any]
List(1,"two").toJson

Why wouldn't that return the same AST I get from this parse?

scala> JsonParser( """[1,"two"]""" )
res22: cc.spray.json.JsValue = [1,"two"]

[sirthias]

Nicholas,
spray-json is completely statically typed, there is no reflection or dynamic inspection of JSON content to figure out some typing on runtime. This means that you cannot convert a List[Any] to JSON (or vice versa), since spray-json does not know how to convert Any to JSON (and vice versa). Any is simply too general. What you are asking for requires dynamic behavior and comes with the respective drawbacks. For example, if you have a List[Any] containing not only Int and String objects but also an object of a custom type Person and you have not defined a JsonFormat[Person] the compiler would not be able to figure out at compile time that something is wrong.
With spray-json this cannot happen.
If it compiles then all the ingredients for successful JSON reading/writing are there...

HTH and cheers,
Mathias

PS: Please use the mailing list for such questions in the future!

[NicholasSterling]

That makes sense -- thanks. Your work on Spray is much appreciated.