Difference in semantics of case classes with Scala 2

[nicolasstucki]

case class Foo(a: Int)(b: Int)

In Scala2, the Foo get equals and hashCode based on only a (parameters in first ()). In Dotty, the methods use on a and b.

Is this intended? Is this specified?

[odersky]

No, I think this is not intended.

[smarter]

This is as specified though I personally find it pretty surprising: http://www.scala-lang.org/files/archive/spec/2.11/05-classes-and-objects.html#case-classes

Method equals: (Any)Boolean is structural equality, where two instances are equal if they both belong to the case class in question and they have equal (with respect to equals) constructor arguments (restricted to the class's elements, i.e., the first parameter section).