Array parameterized with match type causes ClassCastException at runtime

[sbrunk]

It looks like the array is instantiated as Array[Any] / Object[], even though i.e. ScalaType[Float32] resolves to Float.

Compiler version

3.1.3

Minimized code

sealed abstract class DType
sealed class Float16 extends DType
sealed class Float32 extends DType
sealed class Int32 extends DType

object Float16 extends Float16
object Float32 extends Float32
object Int32 extends Int32

type ScalaType[U <: DType] <: Int | Float = U match
  case Float16 => Float
  case Float32 => Float
  case Int32 => Int

class Tensor[T <: DType](dtype: T):
  def toSeq: Seq[ScalaType[T]] = Seq()
  def toArray: Array[ScalaType[T]] = Array()

@main
def main = 
  val t = Tensor(Float32) // Tensor[Float32]
  println(t.toSeq.headOption) // works, Seq[Float]
  println(t.toArray.headOption) // ClassCastException

Output

java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [F ([Ljava.lang.Object; and [F are in module java.base of loader 'bootstrap')

Expectation

toArray should return an Array[Float]

[smarter]

The erased type of def toArray: Array[ScalaType[T]] is Object[] instead of Object (which is the only common superclass of int[] and float[]) which is wrong. By contrast, Array[? <: Int | Float] gets the correct erasure.

[nicolasstucki]

The issue started in ae83f76 of #15606

[smarter]

Are you sure? This issue also exists in 3.1.3 which doesn't include this PR.