Formatting phone numbers in Swift

A simple code snippet to format 10 digit phone numbers in Swift 4.0, instead of including a big library, just implement a delegate function and a formatting function:

• The UITextFieldDelegate function

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    var fullString = textField.text ?? ""
    fullString.append(string)
    if range.length == 1 {
        textField.text = format(phoneNumber: fullString, shouldRemoveLastDigit: true)
    } else {
        textField.text = format(phoneNumber: fullString)
    }
    return false
}

• The formatting function:

func format(phoneNumber: String, shouldRemoveLastDigit: Bool = false) -> String {
    guard !phoneNumber.isEmpty else { return "" }
    guard let regex = try? NSRegularExpression(pattern: "[\\s-\\(\\)]", options: .caseInsensitive) else { return "" }
    let r = NSString(string: phoneNumber).range(of: phoneNumber)
    var number = regex.stringByReplacingMatches(in: phoneNumber, options: .init(rawValue: 0), range: r, withTemplate: "")

    if number.count > 10 {
        let tenthDigitIndex = number.index(number.startIndex, offsetBy: 10)
        number = String(number[number.startIndex..<tenthDigitIndex])
    }

    if shouldRemoveLastDigit {
        let end = number.index(number.startIndex, offsetBy: number.count-1)
        number = String(number[number.startIndex..<end])
    }

    if number.count < 7 {
        let end = number.index(number.startIndex, offsetBy: number.count)
        let range = number.startIndex..<end
        number = number.replacingOccurrences(of: "(\\d{3})(\\d+)", with: "($1) $2", options: .regularExpression, range: range)

    } else {
        let end = number.index(number.startIndex, offsetBy: number.count)
        let range = number.startIndex..<end
        number = number.replacingOccurrences(of: "(\\d{3})(\\d{3})(\\d+)", with: "($1) $2-$3", options: .regularExpression, range: range)
    }

    return number
}

Snippet based on this Objc snippet.

That's it! happy swift phone number formatting!

Photo by James Sutton on Unsplash