FYI in case anyone else will get confused with the content on page 99 / „Listing 4.13 Incrementing and decrementing”
While my version of the book (2015) mentiones those iterators, they are not valid since Swift 3.
source : https://github.com/apple/swift-evolution/blob/master/proposals/0004-remove-pre-post-inc-decrement.md
Hope it will save someone time researching why the code won’t run 