There are many validation libraries for iOS but most of them are tied to the UI. The basic idea is to have a class that encapsulates all the validation logic.
There has been a ton of debate on the swift-evolution mailing lists about access control in Swift. A couple of days ago, the proposal SE-0159: Fix Private Access Levels was rejected.
Attributes improve the efficiency of your codebase, without sacrificing the quality of your code. Jordan Morgan, iOS at Buffer, created a short guide to Swift's attributes.
The iPhone was one of the most exciting new products of this millenia. But as amazing as the device may be, the real superstar is the software that drives it! Take a seat and enjoy our wonderful "Illustrated History of iOS".