Quoted strings in Swift

QuotedString.swift

struct QuotedString : Printable {
    var string: String
    init(_ string: String) {
        self.string = string
    }
    var description: String {
        let backslash: UnicodeScalar = "\\"
        let quote: UnicodeScalar = "\""
        let hex: [UnicodeScalar] = ["0", "1", "2", "3", "4", "5", "6", "7",
                                    "8", "9", "a", "b", "c", "d", "e", "f"]
        var out = ""
        out += "\""
        for u in string.unicodeScalars {
            switch u {
            case backslash: out += "\\\\"
            case quote:     out += "\\\""
            case "\n":      out += "\\n"
            case "\r":      out += "\\r"
            case "\t":      out += "\\t"
            case "\u{0}"..."\u{1f}", "\u{7f}":
                out += "\\u{"
                out.append(hex[Int(u.value) / 16])
                out.append(hex[Int(u.value) % 16])
                out += "}"
            default:
                out.append(u)
            }
        }
        out += "\""
        return out
    }
}

extension String {
    var quote: QuotedString { return QuotedString(self) }
}