One sided ranges

Swift 4 makes it optional to provide a starting index or finishing index of ranges, as used with earlier versions of Swift.

With earlier versions of Swift, you had to do the following to use ranges:

let contactNames = [“Alex”, “Ravi”, “Moin”, “Vlad”, “Mark”]
let firstTwoContacts = contactNames[0..<2]
let lastThreeContacts = contactNames[2..<contactNames.count]
print(firstTwoContacts)
print(lastThreeContacts)

You will get the result as follows:

["Alex", "Ravi"] , for [0..<2]
["Moin", "Vlad", "Mark"], for [2..<contactNames.count]

However, with Swift 4, you no longer have to be constrained to lower bounds or upper bounds of the range mentioned in the for loop mentioned earlier in the code example. You can now use a one sided range where the missing side will automatically be treated as the start or end of a sequence:

let firstTwoContacts = contactNames[..<2]
let lastThreeContacts = contactNames[2...]
print(firstTwoContacts)
print(lastThreeContacts)

You will get the result as shown:

["Alex", "Ravi"] , for [..<2]
 ["Moin", "Vlad", "Mark"] for [2...]