using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("newline\\ntab\\tbackslash\\\\".Unescape());

            //  Test crap detection

        try

        {

            Console.WriteLine("\\x".Unescape());

        }

        catch (Exception ex){

            Console.WriteLine(ex.Message);

        }

​

        try

        {

            Console.WriteLine("x\\".Unescape());

        }

        catch (Exception ex)

        {

            Console.WriteLine(ex.Message);

        }

    }

}

​

public static class StringExtensions

{

    private enum UnescapeState

    {

        Unescaped,

        Escaped

    }

​

    public static String Unescape(this String s)

    {

        var sb = new System.Text.StringBuilder();

        UnescapeState state = UnescapeState.Unescaped;

​

        foreach (var ch in s)

        {

            switch (state)

            {

                case UnescapeState.Escaped:

                    switch (ch)

                    {

                        case 't':

                            sb.Append('\t');

                            break;

                        case 'n':

                            sb.Append('\n');

                            break;

                        case 'r':

                            sb.Append('\r');

                            break;

                        case '\\':

                        case '\"':

                            sb.Append(ch);

                            break;

​

                        default:

                            throw new Exception("Unrecognized escape sequence '\\" + ch + "'");

​

                            //  Finally, what about stuff like '\x0a'? That's a much more 

                            //  complicated state machine. When you see 'x' in Escaped state,

                            //  you transition to UnescapeState.HexDigit0, then either 

                            //  UnescapeState.HexDigit1 or throw an exception, etc. 

                            //  Wicked fun to write. 

                    }

                    state = UnescapeState.Unescaped;

                    break;

​

                case UnescapeState.Unescaped:

                    if (ch == '\\')

                    {

                        state = UnescapeState.Escaped;

                    }

                    else

                    {

                        sb.Append(ch);

                    }

                    break;

            }

        }

​

        if (state == UnescapeState.Escaped)

        {

            throw new Exception("Unterminated escape sequence");

        }

​

        return sb.ToString();

    }

}

​