Should the fields of the base class be considered when implementing hashCode in a data class?

When implementing hashCode in a data class in Kotlin, usually only the properties declared in the data class itself are considered, as the compiler automatically generates equals and hashCode methods based on these properties.

If a base class contains important fields that affect the identity of the object, and you override hashCode in the subclass, you should also consider the fields of the base class to maintain the correctness of the equals and hashCode contracts.

However, in most cases, data classes are not inherited from other classes with additional significant fields, so the standard generation of hashCode is sufficient.

If inheritance is used and the base class has fields that influence comparison, an override might look like this:

override fun hashCode(): Int {
    var result = super.hashCode()
    result = 31 * result + myProperty.hashCode()
    return result
}

In conclusion, consider the fields of the base class when implementing hashCode if they influence the logic of object comparison.