unapplySeq does not support name-based extractors

[smarter]

This is supported in scalac, see tests/pending/run/value-class-extractor-seq.scala.
If you replace the isEmpty method by an isDefined method in ArrayOpt, then compilation fails with:

tests/pending/run/value-class-extractor-seq.scala:46: error: ArrayOpt[Int] is not a valid result type of an unapply method of an extractor

[smarter]

This is also used in tests/pending/run/string-extractor.scala .