Why does this json4s code work in the scala repl but fail to compile?

標籤：

I‘m converting a json-like string into json, and the following code works in the scala repl

import org.json4s._import org.json4s.JsonDSL._import org.json4s.JsonDSL.WithDouble._import org.json4s.native.JsonMethods._val value = "{100:1.50;500:1.00;1000:0.50}"val data = value.stripPrefix("{").stripSuffix("}").split(";").map(a => {  val b = a.split(":")  (b(0),b(1))}).toMapcompact(render(data))

But when it is compiled, I‘m getting the following error

[error] ... type mismatch;[error]  found   : scala.collection.immutable.Map[String,String][error]  required: org.json4s.JValue[error]     (which expands to)  org.json4s.JsonAST.JValue[error]       compact(render(data))[error]                      ^

Why is this, and how might I fix it?

I suspect something with the type system that is over my head.

 

 

up vote2down voteaccepted

render() is imported from JsonMethods._ and it actually requires a JValue. You have imported an implicit map2jvalue twice from those two imports import org.json4s.JsonDSL._ and import org.json4s.JsonDSL.WithDouble._. I suspect that the compiler didn‘t find the implicit due to the ambiguous imports, try to be more selective: the 3rd import seems redundant (the one with JsonDSL.WithDouble._). Sometimes you can run scalac with -Xlog-implicits to see why implicits are not used.

Why does this json4s code work in the scala repl but fail to compile?