Why format combinator does not need underscore in Scala Play JSON Combinators

Question

I found a great explanation of Reads[T] here: Syntax and meaning of a Scala/Play! code sample.

One thing I don't fully understand is why Format[T] does not require the underscore for Creature.apply here:

import play.api.libs.json._
import play.api.libs.functional.syntax._

implicit val creatureFormat = (
  (__ \ "name").format[String] and
  (__ \ "isDead").format[Boolean] and
  (__ \ "weight").format[Float]
)(Creature.apply, unlift(Creature.unapply))

but if this was just Reads[T] the example says

import play.api.libs.json._
import play.api.libs.functional.syntax._

implicit val creatureReads = (
   (__ \ "name").read[String] and
   (__ \ "isDead").read[Boolean] and
   (__ \ "weight").read[Float]
 )(Creature.apply _)

Does Reads not 'require' _ ? In my code using a mix of Reads[T] and Format[T] based on them model and it got me thinking why the difference.

score 1 · Accepted Answer · answered Nov 21 '14 at 14:06

_ following a method indicates partial application.

This is needed when you need to transform a method into a function.

Most of the times you can skip the _ as the compiler is able to infer this from the context and automatically expand the method into a function.

So you can drop the _ in both cases.

Why format combinator does not need underscore in Scala Play JSON Combinators

1 Answers1