Swift 4 'substring(from:)' is deprecated: Please use String slicing subscript with a 'partial range from' operator

Question

i\'ve just converted my little app but i\'ve found this error: \'substring(from:)\' is deprecated: Please use String slicing subscript with a \'partial range from\' operator

Answer 1

Most of my strings have A-Za-z and 0-9 content. No need for difficult Index handling. This extension of String is based on the familiar LEFT / MID and RIGHT functions.

extension String {

    // LEFT
    // Returns the specified number of chars from the left of the string
    // let str = "Hello"
    // print(str.left(3))         // Hel
    func left(_ to: Int) -> String {
        return "\(self[.. String {
        return "\(self[self.index(startIndex, offsetBy: self.length-from)...])"
    }

    // MID
    // Returns the specified number of chars from the startpoint of the string
    // let str = "Hello"
    // print(str.left(2,amount: 2))         // ll
    func mid(_ from: Int, amount: Int) -> String {
        let x = "\(self[self.index(startIndex, offsetBy: from)...])"
        return x.left(amount)
    }
}