独書会 Scala IN DEPTH @夜のイタリアンカフェ その5 ref: http://qiita.com/asmasa/items/26f32f13b7e8af206155

Listing 2.22 Simple InstantaneousTime class

trait InstantaneousTime {
val repr: Int
  override def equals(other: Any) : Boolean = other match {
    case that: InstantaneousTime =>
       if(this eq that) {
         true
       } else {
         (that.## == this.##) &&
         (repr == that.repr)
       }
    case _ => false
}
  override def hashCode() : Int = repr.##
}

Listing 2.23 Event subclass of InstantaneousTime

trait Event extends InstantaneousTime {
  val name: String
  override def equals(other: Any): Boolean = other match {
    case that: Event =>
      if(this eq that) {
        true
      } else {
        (repr == that.repr) &&
        (name == that.name)
      }
    case _ => false
  }
}

Listing 2.24 Using Event and InstantaneousTime

scala> val x = new InstantaneousTime {
     | val repr = 2
     |}
x: java.lang.Object with InstantaneousTime = $anon$1@2
scala> val y = new Event {
     | val name = "TestEvent" | val repr = 2
     |}
y: java.lang.Object with Event = $anon$1@2
scala> y == x
res8: Boolean = false
scala> x == y
res9: Boolean = true

Listing 2.25 Using scala.Equals

trait InstantaneousTime extends Equals {
  val repr: Int
  override def canEqual(other: Any) =
    other.isInstanceOf[InstantaneousTime]
  override def equals(other: Any) : Boolean =
    other match {
      case that: InstantaneousTime =>
        if(this eq that) true else {
             (that.## == this.##) &&
             (that canEqual this) &&
             (repr == that.repr)
        }
    case _ => false
}
  override def hashCode(): Int = repr.hashCode
}
trait Event extends InstantaneousTime {
  val name: String
  override def canEqual(other: Any) =
    other.isInstanceOf[Event]
  override def equals(other: Any): Boolean = other match {
    case that: Event =>
      if(this eq that) {
        true
      } else {
        (that canEqual this) &&
        (repr == that.repr) &&
        (name == that.name)
      }
    case _ => false
  } 
}

Listing 2.26 Using new equals and canEquals methods

scala> val x = new InstantaneousTime {
     | val repr = 2
     |}
x: java.lang.Object with InstantaneousTime = $anon$1@2
scala> val y = new Event {
     | val name = "TestEvent" | val repr = 2
     |}
y: java.lang.Object with Event = $anon$1@2
scala> y == x
res10: Boolean = false
scala> x == y
res11: Boolean = false