scala3 feature examples - opaque types / published by https://github.com/dacr/code-examples-manager #f51b97ee-6fe7-4c76-bc8d-837c7eff6d9e/3ba7febae9ea4c61bcf51090ecd778ea76968d2b

scala3-feature-opaque-types.scala

// summary : scala3 feature examples - opaque types
// keywords : scala3, tutorial, @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 : f51b97ee-6fe7-4c76-bc8d-837c7eff6d9e
// created-on : 2021-03-19T17:06:38+01:00
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

//> using scala "3.1.1"

/*
The perfect feature for Domain Driven Design (DDD) without overhead
*/

import java.util.UUID
import scala.util.Try


object ProjectDefinitions {
  // -- INSIDE OPAQUE TYPES DEFINITIONS SCOPE OPAQUE TYPE RESTRICTION DOESN'T APPLY
  opaque type Email = String
  opaque type UserId = UUID

  object Email {
    def fromString(email: String): Option[Email] = if (checkEmail(email)) Some(email) else None
    def checkEmail(email: String): Boolean = email.matches("""^[A-Za-z0-9+_.-]+@(.+)$""")
  }

  object UserId {
    def fromString(id: String): Option[UserId] = Try(UUID.fromString(id)).toOption
  }
}


@main def go() = {
  import ProjectDefinitions.*
  // -- OUTSIDE OPAQUE TYPES DEFINITIONS SCOPE OPAQUE TYPE RESTRICTION DOES APPLY SO :
  //val myemail:Email = "toto@truc.bidule@@" // it should fail
  //val e1:String = Email.fromString("toto@truc.com").get // it should fail
  //val e2:Email = "toto@truc.com" // it should fail
  Email.fromString("toto@truc.com") match {
    case None => println("Invalid mail")
    case Some(email) => println(email)
  }

  // UUID::version is invisible as type is opaque so no way to have access to its internals
  UserId.fromString("deadbeef-dead-cafe-dead-beefdeadcafe") match {
    case None => println("Invalid userId")
    case Some(userId) => println(userId)
  }
}