Swift – How to use String substring in Swift 4? ‘substring(to:)’ is deprecated: Please use String slicing subscript with a ‘partial range from’ operator

swiftswift4

I have the following simple code written in Swift 3:

let str = "Hello, playground"
let index = str.index(of: ",")!
let newStr = str.substring(to: index)

From Xcode 9 beta 5, I get the following warning:

'substring(to:)' is deprecated: Please use String slicing subscript with a 'partial range from' operator.

How can this slicing subscript with partial range from be used in Swift 4?

Best Answer

You should leave one side empty, hence the name "partial range".

let newStr = str[..<index]

The same stands for partial range from operators, just leave the other side empty:

let newStr = str[index...]

Keep in mind that these range operators return a Substring. If you want to convert it to a string, use String's initialization function:

let newStr = String(str[..<index])

You can read more about the new substrings here.