Disallow Array[Nothing], Array[Null], ... to avoid ClassCastException in some cases #1730
Description
See also https://issues.scala-lang.org/browse/SI-7453
In scalac:
scala> if (false) Array("qwe") else Array()
java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;In dotty, thankfully:
scala> if (false) Array("qwe") else Array()
res1: Array[String] | Array[Nothing] = [Ljava.lang.Object;@1dd92fe2But still in dotty:
scala> val x = if (false) Array("qwe") else Array()
x: Array[String] | Array[Nothing] = [Ljava.lang.Object;@5454d35e
scala> val y: Array[_ <: String] = x
java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;We either need to disallow Array[Nothing], Array[Null], etc or we need to erase Array[_ <: X] to Object instead of [X;.
It would also be much nicer if we could infer the empty array above to have type Array[String] instead of Array[Nothing], I don't know what prevents us from doing this currently.