Swift 2:
A solution is substringFromIndex
let a = "StackOverFlow" let last4 = a.substringFromIndex(a.endIndex.advancedBy(-4)) or suffix on characters
let last4 = String(a.characters.suffix(4)) code is Swift 2
Swift 3:
In Swift 3 the syntax for the first solution has been changed to
let last4 = a.substring(from:a.index(a.endIndex, offsetBy: -4)) Swift 4+:
In Swift 4 it becomes more convenient:
let last4 = a.suffix(4) The type of the result is a new type Substring which behaves as a String in many cases. However if the substring is supposed to leave the scope where it's created in you have to create a new String instance.
let last4 = String(a.suffix(4))