CODEWITHSUNDEEP
scalaplayframework-2.0
gervais.b
gervais.b

Reputation: 2347

Called method was not the one expected

Last week, I spent a lot (too much) of hours on a strange problem. I wanted to use gnieh.diffson to patch an existing object, the client send a PATCH /api/test/patch request with a well formed Json patch. Then I parse the patch and apply it :

import gnieh.diffson._ 
val patch = JsonPatch.parse(request.body.asText.getOrElse("")) 
val workspace = """{"node":{}}""" 
val result = patch(workspace) 
println(result)

This code works fine inside a simple App but fails on a play Controller :

[error] PatchException: : element node does not exist in "{\"node\":{}}" (JsonPatch.scala:140)
[error] gnieh.diffson.Operation.action(JsonPatch.scala:140)
[error] gnieh.diffson.Add.action(JsonPatch.scala:174) ...

The solution was to qualify everything.

The gnieh.diffson.JsonPatch#apply class has 3 apply methods :

def apply(json : scala.Predef.String, compacted : scala.Boolean = { /* compiled code */ }) : scala.Predef.String = { /* compiled code */ } 
def apply(value : net.liftweb.json.JValue) : net.liftweb.json.JValue = { /* compiled code */ } 
def apply[T](<value : T>)(implicit evidence\$1 : scala.Predef.Manifest[T]) : T = { /* compiled code */ }

I was thinking that the first one was called because "workspace" is a String but I was wrong. The called method was the last one, with implicit evidence..

My current solution is to parse the workspace as a net.liftweb.json.JValue but I am not verry happy with it because :
- I can't understant why it is the last method who is called.
- I have to format the net.liftweb.json.JValue to string to recreate a play.api.libs.json.JsObject .. (because I need it later in my process)

Could you please explain me why the called method is the more complex one ?

Thanks a lot

Upvotes: 0

Views: 66

Answers (1)

som-snytt
som-snytt

Reputation: 39577

There's a clause in the contract that discards alternatives that use default args:

http://www.scala-lang.org/files/archive/spec/2.11/06-expressions.html#overloading-resolution

Upvotes: 1

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