Scala semantics of equals/hashCode for case classes with traits
case, equals, hashcode, scala, traits
Solution
Case class equality (particularly in Scala 2.8) equality and hash codes are based upon tuple and/or product equality, and do not currently take the class into account. There was a recent discussion on this matter on the scala-debate mailing list here: http://old.nabble.com/Possible-Collision-Issue-with-Product.hashCode-td27026790.html
For what it's worth, here's what it currently looks like in 2.8:
Welcome to Scala version 2.8.0.Beta1-RC6 (Java HotSpot(TM) Client VM, Java 1.6.0_16).
Type in expressions to have them evaluated.
Type :help for more information.
scala> abstract class C
defined class C
scala> case class CC() extends C
defined class CC
scala> trait T
defined trait T
scala> val c1 = CC()
c1: CC = CC()
scala> val c2 = new CC() with T
c2: CC with T = CC()
scala> println(c1.hashCode == c2.hashCode,c1 equals c2)
(true,true)
Problem
I am a newcomer to Scala. In 2.7.7, the following code ``` abstract class C case class CC() extends C trait T val c1 = CC() val c2 = new CC() with T println(c1.hashCode == c2.hashCode,c1 equals c2) ``` prints ``` (false,true) ``` whereas I would have expected ``` (false,false) ``` What am I missing? Thanks in advance.