Data Classes with Other Properties

You are welcome to have other properties in your data classes, beyond those in the constructor:

data class Animal(val species: String, val ageInYears: Float) {
  var isFriendly = true
  var isHungry = true
  val isCommonlySeenFlyingInTornadoes = false
}

However, code-generated functions, like equals() and copy(), will ignore these properties. Those functions only incorporate the properties defined in the primary constructor.

Sometimes, this can be a feature: you might want some properties to be ignored for equals() and hashCode(). Sometimes, this can be a bug: you might not realize that copy() only copies a subset of your properties.