A Swift string extension for adding leading ellipsis

LeadingEllipsis.swift

extension String {

    func stringByTruncatingLeadingForWidth(width: CGFloat, withFont font: UIFont) -> String{

        var modifiedString = self
        var mutableWidth = width
        let ellipsis = "..."
        if (self.widthOfString(usingFont: font) > width) {
            let ellipsisWidth = ellipsis.widthOfString(usingFont: font)

            // else this will go for infinite loop...mutable width will go -ve
            if mutableWidth > ellipsisWidth {
                mutableWidth -= ellipsis.widthOfString(usingFont: font)
            }
            let range = NSMakeRange(0, 1)

            while modifiedString.widthOfString(usingFont: font) > mutableWidth {
                modifiedString.deleteCharactersInRange(range: range)
                print(modifiedString)
                print(mutableWidth)
            }
            guard let swiftRange = Range(NSMakeRange(0, 3), in: modifiedString) else { return ""  }
            modifiedString.replaceSubrange(swiftRange, with: [".",".","."])
        }
        return modifiedString
    }
    func widthOfString(usingFont font: UIFont) -> CGFloat {
        let fontAttributes = [NSAttributedString.Key.font: font]
        let size = self.size(withAttributes: fontAttributes)
        return size.width
    }

    mutating func deleteCharactersInRange(range: NSRange) {
        guard let swiftRange = Range(range, in: self) else { return  }
        self.removeSubrange(swiftRange)
    }
}

var str1 = "Hello how are you"

let newStr = str1.stringByTruncatingLeadingForWidth(width: 100, withFont: .systemFont(ofSize: 15))