Understanding the removeRange(_:) documentation

Question

To remove a substring at a specified range, use the removeRange(_:) method:

1 let range = advance(welcome.endIndex, -6)..

        

Answer 1

Swift 2

We're going to use var since removeRange needs to operate on a mutable string.

var welcome = "hello there"

This line:

let range = welcome.endIndex.advancedBy(-6)..<welcome.endIndex

means that we start from the end of the string (welcome.endIndex) and move back by 6 characters (advance by a negative number = move back), then ask for the range (..<) between our position and the end of the string (welcome.endIndex).

It creates a range of 5..<11, which encompasses the " there" part of the string.

If you remove this range of characters from the string with:

welcome.removeRange(range)

then your string will be the remaining part:

print(welcome) // prints "hello"

You can take it the other way (from the start index of the string) for the same result:

welcome = "hello there"
let otherRange = welcome.startIndex.advancedBy(5)..<welcome.endIndex
welcome.removeRange(otherRange)
print(welcome) // prints "hello"

Here we start from the beginning of the string (welcome.startIndex), then we advance by 5 characters, then we make a range (..<) from here to the end of the string (welcome.endIndex).

Note: the advance function can work forward and backward.

Swift 3

The syntax has changed but the concepts are the same.

var welcome = "hello there"
let range = welcome.index(welcome.endIndex, offsetBy: -6)..<welcome.endIndex
welcome.removeSubrange(range)
print(welcome) // prints "hello"

welcome = "hello there"
let otherRange = welcome.index(welcome.startIndex, offsetBy: 5)..<welcome.endIndex
welcome.removeSubrange(otherRange)
print(welcome) // prints "hello"