StableName.scala

sealed class StableName[A] extends Serializable
object StableName {
  private[this] final class RefInstance[A <: AnyRef](val value: A) extends StableName[A] {
    override def clone(): AnyRef = this

    override def equals(obj: Any): Boolean = obj match {
      case that: RefInstance[_] => that.value eq this.value
      case _ => false
    }

    override def hashCode(): Int =
      System.identityHashCode(value)
  }

  private[this] final case object UnitInstance extends StableName[Unit]
  private[this] final case object NullInstance extends StableName[Unit]

  private[this] final case class ByteInstance(value: Byte)     extends StableName[Byte]
  private[this] final case class ShortInstance(value: Short)   extends StableName[Short]
  private[this] final case class IntInstance(value: Int)       extends StableName[Int]
  private[this] final case class LongInstance(value: Long)     extends StableName[Long]
  private[this] final case class FloatInstance(value: Float)   extends StableName[Float]
  private[this] final case class DoubleInstance(value: Double) extends StableName[Double]

  def makeFromRef[A <: AnyRef](value: A): UIO[StableName[A]] =
    UIO { new RefInstance[A](value) }

  def make[A](value: A): UIO[StableName[A]] =
    UIO {
      value match {
        case ()   => UnitInstance.asInstanceOf[StableName[A]]
        case null => NullInstance.asInstanceOf[StableName[A]]

        case v: Byte   => ByteInstance(v).asInstanceOf[StableName[A]]
        case v: Short  => ShortInstance(v).asInstanceOf[StableName[A]]
        case i: Int    => IntInstance(i).asInstanceOf[StableName[A]]
        case i: Long   => LongInstance(i).asInstanceOf[StableName[A]]
        case i: Float  => FloatInstance(i).asInstanceOf[StableName[A]]
        case i: Double => DoubleInstance(i).asInstanceOf[StableName[A]]

        case v: AnyRef => new RefInstance(v).asInstanceOf[StableName[A]]
        case _ => sys.error("impossible")
      }
    }

  implicit def eqInstance[A]: Eq.Univ[StableName[A]] =
    Eq.fromUniversalEquals[StableName[A]]
}