Atom "Constructors & Exceptions", CodeListing.scala

[vivian-duong]

Probably only became an issue with Scala updates. It's an issue in Scala 2.13.1.

In CodeListing.scala,we should change class CodeListing(val fileName:String) extends collection.IndexedSeq[String] to class CodeListing(val fileName:String) extends collection.immutable.IndexedSeq[String]. If not, when we run scala CodeListingTest.scala, we get the following error

error: type mismatch;
 found   : IndexedSeq[String] (in scala.collection)
 required: IndexedSeq[String] (in scala.collection.immutable)
new CodeListingTester(CodeListing.apply)