Added alignment support for named values.

string-format-extension.cs

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.UI;

namespace StringExtensions
{
	/// <remarks>
	/// http://james.newtonking.com/archive/2008/03/27/formatwith-string-format-extension-method.aspx
	/// http://james.newtonking.com/archive/2008/03/29/formatwith-2-0-string-formatting-with-named-variables.aspx
	/// http://haacked.com/archive/2009/01/14/named-formats-redux.aspx
	/// </remarks>
	public static class JamesFormatter
	{
		static readonly Regex NamedFormatRegex = new Regex(@"(?<start>\{)+(?<property>[\w\.\[\]]+)(?<align>,\-?\d+)?(?<format>:[^}]+)?(?<end>\})+", RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);

		public static string FormatWith(this string format, object source)
		{
			return FormatWith(format, null, source);
		}

		public static string FormatWith(this string format, IFormatProvider provider, object source)
		{
			if (format == null) throw new ArgumentNullException("format");

			var values = new List<object>();
			string rewrittenFormat = NamedFormatRegex.Replace(format, delegate(Match m)
			{
				Group startGroup = m.Groups["start"];
				Group propertyGroup = m.Groups["property"];
				Group alignGroup = m.Groups["align"];
				Group formatGroup = m.Groups["format"];
				Group endGroup = m.Groups["end"];

				values.Add((propertyGroup.Value == "0") ? source : Eval(source, propertyGroup.Value));

				int openings = startGroup.Captures.Count;
				int closings = endGroup.Captures.Count;

				return openings > closings || openings % 2 == 0 ? m.Value : new string('{', openings) + (values.Count - 1) + alignGroup.Value + formatGroup.Value + new string('}', closings);
			});

			return string.Format(provider, rewrittenFormat, values.ToArray());
		}

		private static object Eval(object source, string expression)
		{
			try
			{
				return DataBinder.Eval(source, expression);
			}
			catch (HttpException e)
			{
				throw new FormatException(null, e);
			}
		}
	}
}