Question

Let’s say that I have this class

case class Test (id: Long, name: String)

and an instance of this class :

Test :
id -> 1
name -> toto

I would like to create a Map[String, String] as follow :

Map( "id" -> "1", "name" -> "toto")

My question is : Is there a way to turn this instance of Test into Map[String, String] ? I want to avoid to use a method as this one :

def createMap(instance: Test): Map[String, String] = {
    val map = new Map[String, String]
    map.put("id", instance.id.toString)
    map.put("name", instance.name)
    map
}

If there is no method to do so in Scala, is there a way to iterate over class properties ? Maybe I can create a generic function to do so :

def createMap(instance: T): Map[String, String] = {
   val map = new Map[String, String]
   //pseudocode 
   for  ((name, value) <- instance.getClassProperties.getValues) {
      case value.isInstanceOf[String] : map.push(name, value)
      case _ : map.push(name, value.toString)
    }
    map
}

Is that possible ? If you have good examples/links, I’m interested.

Answer 1

Yes it’s possible. Since Scala 2.10 you can use reflection.

Assuming you have:

val test = Test(23423, "sdlkfjlsdk")

The following will get you what you want:

import reflect.runtime.universe._
import reflect.runtime.currentMirror

val r = currentMirror.reflect(test)
r.symbol.typeSignature.members.toStream
  .collect{case s : TermSymbol if !s.isMethod => r.reflectField(s)}
  .map(r => r.symbol.name.toString.trim -> r.get.toString)
  .toMap

To simply iterate over field values of case class use .productIterator on its instance.