StringBuilder - ExtractStringArobasDoubleQuote

A StringBuilder extension method that extracts the string arobas double quote described by @this.

Try it

public static void Main()
{
    int endIndex;

    // C# Extension Method: StringBuilder - ExtractStringArobasDoubleQuote
    Console.WriteLine(new StringBuilder(" ").ExtractStringArobasDoubleQuote());
    Console.WriteLine(new StringBuilder("@\"z\"").ExtractStringArobasDoubleQuote().ToString());
    Console.WriteLine(new StringBuilder("@@\"z\"z").ExtractStringArobasDoubleQuote(1, out endIndex).ToString());
    Console.WriteLine(endIndex);
}

View Source
using System;
using System.Text;

public static partial class Extensions
{
    /// <summary>
    ///     A StringBuilder extension method that extracts the string arobas double quote
    ///     described by @this.
    /// </summary>
    /// <param name="this">The @this to act on.</param>
    /// <returns>The extracted string arobas double quote.</returns>
    public static StringBuilder ExtractStringArobasDoubleQuote(this StringBuilder @this)
    {
        return @this.ExtractStringArobasDoubleQuote(0);
    }

    /// <summary>
    ///     A StringBuilder extension method that extracts the string arobas double quote
    ///     described by @this.
    /// </summary>
    /// <param name="this">The @this to act on.</param>
    /// <param name="endIndex">[out] The end index.</param>
    /// <returns>The extracted string arobas double quote.</returns>
    public static StringBuilder ExtractStringArobasDoubleQuote(this StringBuilder @this, out int endIndex)
    {
        return @this.ExtractStringArobasDoubleQuote(0, out endIndex);
    }

    /// <summary>
    ///     A StringBuilder extension method that extracts the string arobas double quote
    ///     described by @this.
    /// </summary>
    /// <exception cref="Exception">Thrown when an exception error condition occurs.</exception>
    /// <param name="this">The @this to act on.</param>
    /// <param name="startIndex">The start index.</param>
    /// <returns>The extracted string arobas double quote.</returns>
    public static StringBuilder ExtractStringArobasDoubleQuote(this StringBuilder @this, int startIndex)
    {
        int endIndex;
        return @this.ExtractStringArobasDoubleQuote(startIndex, out endIndex);
    }

    /// <summary>
    ///     A StringBuilder extension method that extracts the string arobas double quote
    ///     described by @this.
    /// </summary>
    /// <exception cref="Exception">Thrown when an exception error condition occurs.</exception>
    /// <param name="this">The @this to act on.</param>
    /// <param name="startIndex">The start index.</param>
    /// <param name="endIndex">[out] The end index.</param>
    /// <returns>The extracted string arobas double quote.</returns>
    public static StringBuilder ExtractStringArobasDoubleQuote(this StringBuilder @this, int startIndex, out int endIndex)
    {
        var sb = new StringBuilder();

        if (@this.Length > startIndex + 1)
        {
            var ch1 = @this[startIndex];
            var ch2 = @this[startIndex + 1];

            if (ch1 == '@' && ch2 == '"')
            {
                // @"my string"

                var pos = startIndex + 2;

                while (pos < @this.Length)
                {
                    var ch = @this[pos];
                    pos++;

                    if (ch == '"' && pos < @this.Length && @this[pos] == '"')
                    {
                        sb.Append(ch);
                        pos++; // Treat as escape character for @"abc""def"
                    }
                    else if (ch == '"')
                    {
                        endIndex = pos;
                        return sb;
                    }
                    else
                    {
                        sb.Append(ch);
                    }
                }

                throw new Exception("Unclosed string starting at position: " + startIndex);
            }
        }

        endIndex = -1;
        return null;
    }
}