value class scala feature / published by https://github.com/dacr/code-examples-manager #0dbdfc09-d86a-4943-8f0d-62d98399fea8/a4303a017a915f520f774f3829dc5723e16d1031

scala-feature-value-class.sc

// summary : value class scala feature
// keywords : scala, language-feature, performance, domain-model, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : 0dbdfc09-d86a-4943-8f0d-62d98399fea8
// created-on : 2021-04-05T16:56:55Z
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala "3.4.2"
//> using objectWrapper
// ---------------------
import java.time.*

// https://dzone.com/articles/what-value-classes-is

println("A value class has only one parameter but can have defs")
println("Typically to give a type to a tiny type : UserId, UserName, CloudId, ...")
class UserId(val id:Int) extends AnyVal

println(UserId(2).id)

class Euros(val amount:Long) extends AnyVal:
  override def toString: String = s"${amount}€"
  def add(that:Euros):Euros = Euros(amount+that.amount)

println(Euros(20).add(Euros(22)))

class When(val timestamp:Long) extends AnyVal:
  override def toString: String = Instant.ofEpochMilli(timestamp).toString

def f1(amount: Long, when:Long) = s"when:$when amount:${amount}€"
def f2(amount: Euros, when:When) = s"when:$when amount:$amount"

println(f1(10L, System.currentTimeMillis))
println(f1(System.currentTimeMillis(), 10L))   // Easy to give the wrong parameter

println(f2(Euros(10), When(System.currentTimeMillis)))

println(
  """Value classes are interesting
    | - for domain modelling and avoid using the same types everywhere (String for everything, ...)
    | - for performance optimization and memory optimization
    | """.stripMargin
)
println("The generated bytecode will unwrap the value class, using directly the parameter type and thus avoid overhead ")