How To Access access Case class field Value from String name of the field

Question

How should I extract the value of a field of a case class from a given String value representing the field.

For example:

case class Person(name: Stri         


        

Answer 1

What you're looking for can be achieve using Shapeless lenses. This will also put the constraint that a field actually exists on a case class at compile time rather than run time:

import shapeless._

case class Person(name: String, age: Int)

val nameLens = lens[Person] >> 'name
val p = Person("myName", 25)

nameLens.get(p)

Yields:

res0: String = myName

If you try to extract a non existing field, you get a compile time error, which is a much stronger guarantee:

import shapeless._

case class Person(name: String, age: Int)

val nonExistingLens = lens[Person] >> 'bla
val p = Person("myName", 25)

nonExistingLens.get(p)

Compiler yells:

Error:(5, 44) could not find implicit value for parameter mkLens: shapeless.MkFieldLens[Person,Symbol with shapeless.tag.Tagged[String("bla")]]
val nonExistingLens = lens[Person] >> 'bla