A static class that allows you to use name/value pairs from an dictionary to substitute string-representations of object values - this extension complements String.Format()

StringSubstitutionExtension.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Mindplay.Extensions
{
    /// <summary>
    /// This extension provides an alternative to <see cref="String.Format"/> allowing the
    /// use of an <see cref="IDictionary{String,Object}"/> to replace named (rather than
    /// numbered) tokens in a string template.
    /// 
    /// Usage is Similar to that of String.Format(), but the string templates use names
    /// instead of numbers when referencing the values to substitute - and the input is
    /// a dictionary rather than an array.
    /// 
    /// The following unit test provides a demonstration of how to use this extension:
    /// 
    /// <code>
    /// var replacements = new Dictionary<String, object>()
    ///                        {
    ///                            { "date1", new DateTime(2009, 7, 1) },
    ///                            { "hiTime", new TimeSpan(14, 17, 32) },
    ///                            { "hiTemp", 62.1m },
    ///                            { "loTime", new TimeSpan(3, 16, 10) },
    ///                            { "loTemp", 54.8m }
    ///                        };
    /// 
    /// var template =
    ///     "Temperature on {date1:d}:\n{hiTime,11}: {hiTemp} degrees (hi)\n{loTime,11}: {loTemp} degrees (lo)";
    /// 
    /// var expected = "Temperature on 7/1/2009:\n   14:17:32: 62.1 degrees (hi)\n   03:16:10: 54.8 degrees (lo)";
    /// 
    /// var result = template.Subtitute(replacements);
    /// 
    /// Assert.IsTrue(
    ///     result == expected,
    ///     "string template mismatch:\n" + result + "\nexpected:\n" + expected);
    /// </code>
    /// 
    /// You may contrast this example with the reference example provided for String.Format():
    /// 
    /// http://msdn.microsoft.com/en-us/library/1ksz8yb7.aspx
    /// </summary>
    public static class StringSubstitutionExtension
    {
        private static readonly Regex Pattern = new Regex(@"(?<!\{)\{(\w+)([^\}]*)\}");

        /// <summary>
        /// Replaces the format item in a specified string with the string representation of a corresponding object in a specified dictionary.
        /// </summary>
        public static String Subtitute(this String template, IDictionary<String,Object> dictionary)
        {
            return Subtitute(template, null, dictionary);
        }

        /// <summary>
        /// Replaces the format item in a specified string with the string representation of a corresponding object in a specified dictionary.
        /// A specified parameter supplies culture-specific formatting information.
        /// </summary>
        public static String Subtitute(this String template, IFormatProvider formatProvider, IDictionary<String,Object> dictionary)
        {
            var map = new Dictionary<String,int>();

            var list = new List<Object>();

            var format = Pattern.Replace(
                template,
                match =>
                    {
                        var name = match.Groups[1].Captures[0].Value;

                        if (!map.ContainsKey(name))
                        {
                            map[name] = map.Count;
                            list.Add(dictionary.ContainsKey(name) ? dictionary[name] : null);
                        }

                        return "{" + map[name] + match.Groups[2].Captures[0].Value + "}";
                    }
                );

            return formatProvider == null
                ?
                String.Format(format, list.ToArray()) 
                :
                String.Format(formatProvider, format, list.ToArray());
        }
    }
}

I wrote this extension in response to the following stackexchange.com question:

http://stackoverflow.com/questions/379328/c-named-parameters-to-a-string-that-replace-to-the-parameter-values/5503565#5503565