Play framework - pass parameter to Writes and Reads - json

Question

Is there a way to pass parameter into a Writes to I will be able to control they way the JsValue is written?
This is how it looks right now:
implicit val myClassWrites = new Writes[MyClass] {
override def writes(l: MyClass): JsValue = Json.obj("a" -> l.a, "b" -> l.b)
}
But I want to do something like this:
implicit val myClassWrites = new Writes[MyClass] (extended: Option[Boolean]) {
override def writes(l: MyClass): JsValue = {
extended match{
case true => //do something
case false => //do something else
}
}
}
Is there an elegant way to achieve this? or something similar?
I managed do implement this need with Reads like this(dropping the implicit):
def myClassReads(c: String) : Reads[MyClass] = (
Reads.pure(c) and
(JsPath \ "a").read[String] and
(JsPath \ "b").read[String]
) (MyClass.apply _)
And then when I want to use the reads (usually in the controller when I want to validate the body of the request) I do:
request.body.validate[MyClass](MyClass.myClassReads("foo")).fold(
errors => //
myClass=> // do domething
)
So the Writes is still a mystery.

Answer 1

You can do this with implicit parameters. See code below:
case class Extended(b: Boolean)
object MyClass {
implicit def MyClassWrites(implicit extended: Extended): Writes[MyClass] = new Writes[MyClass] {
def writes(l: MyClass) =
if (extended.b) JsString("foo")
else JsString("bar")
}
}
And then use like this
implicit var extd = Extended(true)
println(Json.toJson(myClass)) // foo
extd = Extended(false)
println(Json.toJson(myClass)) // bar