Question

I have the following code, which works, but I’m wondering if there is a “groovier” way of doing this:

/**
   * 10 digit - #-######-##-#
   * 13 digit - ###-#-######-##-#
   * */
private formatISBN(String isbn) {
  if (isbn?.length() == 10) {
    def part1 = isbn.substring(0, 1)
    def part2 = isbn.substring(1, 7)
    def part3 = isbn.substring(7, 9)
    def part4 = isbn.substring(9, 10)
    return "${part1}-${part2}-${part3}-${part4}"
  } else if (isbn?.length() == 13) {
    def part1 = isbn.substring(0, 3)
    def part2 = isbn.substring(3, 4)
    def part3 = isbn.substring(4, 10)
    def part4 = isbn.substring(10, 12)
    def part5 = isbn.substring(12, 13)
    return "${part1}-${part2}-${part3}-${part4}-${part5}"
  } else {
    return isbn
  }
}

Answer 1

Dunno if I like this any better. I’d make the position map a static final, too.

private isbnify(String isbn) {
  def dashesAt = [ 10: [[0,1], [1,7], [7,9],  [9,10]],
                   13: [[0,3], [3,4], [4,10], [10,12], [12,13]]]
  def dashes = dashesAt[isbn?.length()]
  (dashes == null) ? isbn 
                   : dashes.collect { isbn.substring(*it) }.join('-')
}

Ranges make for a bit less clutter, IMO:

private isbnify3(String isbn) {
  def dashesAt = [ 10: [0, 1..6, 7..8, 9],
                   13: [0..2, 3, 4..9, 10..11, 12]]
  def dashes = dashesAt[isbn?.length()]
  dashes == null ? isbn : dashes.collect { isbn[it] }.join("-")
}

With an inject-with-two-accumulators it should be easy to do a list-of-dash-positions version, too.