What is the reason enumeration does not derive CanEqual?
It was very surprising that this is not the default case, which led me to submit the following issue:
However, only after I noticed that the test cases explicitly check the interaction of enums and strictEquality, I understood that this is an intended design decision.
I started experimenting with strictEquality just recently. Once it’s on it pretty much requires you to have it specified on every case class that will participate in pattern matching.
IME so far it’s strictly worse than Scala 2’s linting support + -Xfatal-warnings.
In Scala 2 you do literally nothing and get actionable errors for the cases you care about (i.e. where you are mistakenly comparing values of different types).
In Scala 3 you have to pepper derives CanEqual on every non-primitive type where you’ll be doing equality checking.
For example, here are some ScalaTest failures that have me considering giving up and disabling strictEquality in sbt test scope.
assert(x == Some(model))
Values of types Option[User] and Some[User] cannot be compared with == or !=
assert(x == List(model))
Values of types List[User] and List[User] cannot be compared with == or !=
Compared to Scala 2 it’s kind of like the tail wagging the dog, but I guess this is the only solution until linting support lands in Scala 3.