Scala : Add an implicit method to transform case class to another case class in alias object?

Question

I am new to Scala and I have a case class like this:

case class Student(
 name: String,
 age: Option[Int] = None,
 id: String
)

and another case class like this:

case class Member(
 id: String,
 `type`: String,
 name: String
)

I want to create a helper implicit in such a way that:

case class Member(
 id: String,
 `type`: String,
 name: String
)

object Member {
  implicit def toStudent(member:Member):Student = Student(member.name,None,member.id)
}

and then call the method like this:

val newMember = Member("abc","Student","John")
val student = newMember.toStudent

or something fancy like that. Would this be possible in Scala as I see a lot of fancy syntax similar to this at a lot of places?

Why an extension rather than defining the method directly on the class? — Luis Miguel Mejía Suárez, Nov 09 '22 at 15:38
_"We wanted to have it on case class"_ so what? Just define it in the case class body — Luis Miguel Mejía Suárez, Nov 10 '22 at 12:27

Guru Stron · Accepted Answer · 2022-11-09T11:12:16.423

3

In Scala 3 you can use extensions methods:

// ...

extension (member: Member)
  def toStudent: Student = Student(member.name, None, member.id)

val newMember = Member("abc", "Student", "John")
val student = newMember.toStudent

For Scala 2 you can define explicit conversion:

import scala.language.implicitConversions
object Member {
  implicit def toStudent(member: Member): Student =
    Student(member.name, None, member.id)
}

val newMember = Member("abc", "Student", "John")
val student = newMember: Student

Or using implicit class decorator:

implicit class MemberDecorator(val member: Member) extends AnyVal {
  def toStudent(): Student = Student(member.name, None, member.id)
}

val newMember = Member("abc", "Student", "John")
val student = newMember.toStudent()

edited Nov 09 '22 at 11:12

answered Nov 09 '22 at 10:58

Guru Stron

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I see but currently my whole production code is on Scala 2.13 – Shivam Sahil Nov 09 '22 at 11:05
Hmm I tried what you shared but its not working, the implicit that you have declared is it supposed to be placed in helper object or where? If I put it in helper object it fails and says cannot find the method I think you can create those implicits only within a class – Shivam Sahil Nov 09 '22 at 11:41
1

@ShivamSahil GuruStron's code compiles https://scastie.scala-lang.org/DmytroMitin/VD5LfcQUTo6wb06oErvukQ/1 https://scastie.scala-lang.org/DmytroMitin/VD5LfcQUTo6wb06oErvukQ/2 – Dmytro Mitin Nov 09 '22 at 11:53
1

@ShivamSahil [Where does Scala look for implicits?](https://stackoverflow.com/questions/5598085/where-does-scala-look-for-implicits) – Dmytro Mitin Nov 09 '22 at 11:54
@DmytroMitin, I see thank you very much for the entire code in playground. I see you do the conversion as: `val student = newMember: Student` however I was trying out: `newMember.toStudent` But thanks anyways, this is what I needed. – Shivam Sahil Nov 09 '22 at 12:00
2

@ShivamSahil Can't you see `newMember.toStudent` at the 2nd link https://scastie.scala-lang.org/DmytroMitin/VD5LfcQUTo6wb06oErvukQ/2 ? – Dmytro Mitin Nov 09 '22 at 12:24
@DmytroMitin Oh sorry I missed it but now I see... However the implicit declaration is supposed to be in some object right? I had a standalone scala file where I had these case classes and I was trying to put `implicit class` there and that's what was throwing me an error but thank you very much again! Now I understand it completelt – Shivam Sahil Nov 09 '22 at 12:54
2

@ShivamSahil Preferably not some object but companion object https://scastie.scala-lang.org/DmytroMitin/VD5LfcQUTo6wb06oErvukQ/3 Please read "Where does Scala look for implicits?" – Dmytro Mitin Nov 09 '22 at 13:06

Scala : Add an implicit method to transform case class to another case class in alias object?

1 Answers1