How can I use String substring in Swift 4? 'substring(to:)' is deprecated: Please use String slicing subscript with a 'partial range from' operator

Question

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?

Answer 1

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.

Answer 2

Convert Substring (Swift 3) to String Slicing (Swift 4)

Examples In Swift 3, 4:

let newStr = str.substring(to: index) // Swift 3 let newStr = String(str[..<index]) // Swift 4 

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let newStr = str.substring(from: index) // Swift 3 let newStr = String(str[index...]) // Swift 4  

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let range = firstIndex..<secondIndex // If you have a range let newStr = = str.substring(with: range) // Swift 3 let newStr = String(str[range])  // Swift 4