opaque type

object Company {
  opaque type Name = String

  object Name {
    def apply(s: String): Name = s
  }

  extension (name: Name) def length: Int = name.length

  // inside: Name <-> String
  def fullName(first: Name, second: Name): Name = {
    first.concat(second) // String 의 method 를 사용 가능
  }
}

@main def Main(): Unit = {
  import Company.*

  // Outside, Name & String are NOT related
  val first: Name = "First" // NOT allowed, Error !!!

  val fn: Name = fullName(Name("First"), Name("Second")) // OK
  println(fn.length) // 11 extension method 를 통해 String 의 length 만 노출
}