反変、共変周りの練習

parameter.scala

class Publication(val title: String)

class Book(title: String) extends Publication(title)

object Library {
  val books: Set[Book] = Set(new Book("Programming in Scala"), new Book("Walden"))

  def printBookList(info: Book => AnyRef) = {
    for (book <- books) println(info(book))
  }
}

object Customer extends App {
  def getTitle(p: Publication): String = p.title

  Library.printBookList(getTitle)
}