How to implement case class manually. (for Scala 2.9.2 final)

Id.scala

import scala.runtime.ScalaRunTime

/**
 * A sample code to implement a customized case class manually (for Scala 2.9.2 final).
 *
 * Id has two properties: name and displayName. 'displayName' has default value that
 * is same value as 'name'.
 */
class Id private ( // make primary constructor not to be accessible. (standard case class can do)

  val name: String,

  val displayName: String,

) extends Product with Serializable { // inherits from Product and Serializable.

  // implement copy method manually.
  def copy(
      name: String = this.name,
      displayName: String = this.displayName) =
    Id.apply(name, displayName)

  // Product (used by Scala runtime)

  override def productPrefix = classOf[Id].getSimpleName

  def productArity = 2

  def productElement(n: Int): Any = n match {
    case 0 => this.id
    case 1 => this.displayName
    case _ => throw new IndexOutOfBoundsException(n.toString)
  }

  def canEqual(that: Any) = that.isInstanceOf[Id]

  // NOTE: Scaladoc of ScalaRunTime says that "All these methods should be considered
  // outside the API and subject to change or removal without notice."
  override def equals(that: Any) = ScalaRunTime._equals(this, that)

  // Object (AnyRef)

  override def hashCode() = ScalaRunTime._hashCode(this)

  override def toString = ScalaRunTime._toString(this)

}

object Id {

  // exclusive factory method
  def apply(
      name: String,
      displayName: String = null) = displayName match {
    case null => new Id(name, name)
    case _ => new Id(name, displayName)
  }

  // for pattern matching
  def unapply(id: Id) = Some((id.name, id.displayName))

}

ScalaRuntime.*s are no longer used by the compiller.

See also:

• http://caoilte.org/scala/2014/10/06/bending-jaxb-to-the-will-of-scala-2-of-2/
• http://stackoverflow.com/questions/11395127/rename-and-override-equals-method-in-case-class/11396362#11396362
• https://groups.google.com/d/msg/scala-user/EfEb8MPa5BM/OA_rVHOfEoMJ