Default Initializer + intersection with Nothing = CCE

[sir-wabbit]

scala> val a : Int with Nothing = a
                                  ^
       warning: value a does nothing other than call itself recursively
a: Int with Nothing = 0

scala> val b : Nothing = a
java.lang.ClassCastException: java.lang.Integer cannot be cast to scala.runtime.Nothing$
  ... 40 elided

Tested in 2.13.0-M3 REPL

[milessabin]

If you assert false I think the compiler is entitled to respond any way it pleases ;-)

[sir-wabbit]

A slightly different example:

scala> val a: Int with Nothing = identity(a)
a: Int with Nothing = 0

scala> a.equalsIgnoreCase("a")
java.lang.ClassCastException: java.lang.Integer cannot be cast to scala.collection.immutable.StringOps
  ... 40 elided

[SethTisue]

Scala 3's behavior is the same on the original example, except that you don't even get the warning.

The second example gives "value equalsIgnoreCase is not a member of Int & Nothing".

[som-snytt]

Dotty warns on implicit only FSR

scala> implicit val a : Int with Nothing = a
1 warning found
-- Warning: ------------------------------------------------------------------------------------------------------------
1 |implicit val a : Int with Nothing = a
  |                                    ^
  |                                    Infinite loop in function body
  |                                    a
val a: Int & Nothing = 0

[SethTisue]

the SR is that people were getting bitten fairly often, as per scala/scala3#9880 — see also more history at scala/scala3#13709 and a few other issues and PRs a click or two farther away

whereas I doubt the givenless, implicitless version triggers very often in the wild