nicolasstucki/scala-days-2023

Scala Days 2023 - Implementing a Macro in Scala 3

Scala Days Presentation

• Talk: https://www.youtube.com/watch?v=dKblZynnhgo
• Slides: https://nicolasstucki.github.io/scala-days-2023/

Usage

This is a normal sbt project. You can compile code with sbt compile, test it with sbt test, and sbt console will start a Scala 3 REPL.

JSON representation

type Json = JsonObject | JsonArray | Double | String | Boolean | Null

Macro JSON string interpolation

The string interpolator json defined in JsonStringContext.scala provides shows how to implement the interpolator apply and unapply with macros.

Crate refined JSON with an interpolator

val user = json"""{
    "firstName": "John",
    "lastName": "Doe"
  }"""
val bool = json"true"
val account = json"""{
    "user": $user,
    "active": $bool
}"""

where the type of account is refined to

account: JsonObject {
  val user: JsonObject {
    val firstName: String
    val lastName:String
  }
  val active: Boolean
}

Extracting refined JSON with an interpolator

(account: Json) match
  case json"""{ "user": $x, "active": true }""" => println(x + " is active")
  case _ =>