What is a good way to handle default values with s

问题:

In some cases default values make more sense than optionals in case classes:

case class Car(numberOfWheels:Int = 4, color:String)

case class Car(numbeOfWheels:Option[Int], color:String) //silly

In the first case I'd expect to be able to easily convert the following json to an instance:

{"color":"red"}

But with a standard jsonFormat2(Car), spray-json complains about missing value for numberOfWheels.

How do I work around this most cleanly?

回答1:

I stumbled upon the same problem. I've create a patch that solves it for me. It makes fields with a default value optional.

https://github.com/spray/spray-json/pull/56

update: PR is updated and still open https://github.com/spray/spray-json/pull/93

回答2:

I have never used spray, but here's my guess about what may work:

case class Car(numberOfWheels: Int, color: String) {
  def this(color: String) = this(4, color)
}

object Car {
  def apply(color: String) = new Car(color)
}

Maybe now jsonFormat1(Car) will work.