Partially Available Extension Methods in C#

Some C# 3 features can be used in .NET 2.0 with a declaration. Extension methods require an attribute which is normally part of .NET 3.5. However, this is an example of features which can be enabled.

Extension methods usually take the following form:

namespace Extensions
{
	public static partial class DateTimeExtensions
	{
		/// <summary>
		/// 	Creates a string in the Hammer format from a DateTime object
		/// </summary>
		/// <param name="dateTime">The DateTime object.</param>
		/// <returns>A string in the Hammer format</returns>
		public static string ToHammerTimeString(this DateTime dateTime)
		{
			return dateTime.ToString("ddHHmm'Hammer'MMMyyyy");
		}

		/// <summary>
		/// 	Creates a new instance of a DateTime object from a string in the Hammer format
		/// </summary>
		/// <param name="dateTime">The DateTime object.</param>
		/// <param name="input">The input sting.</param>
		/// <returns>A DateTime object</returns>
		public static DateTime CreateFromHammerTimeString(this DateTime dateTime, string input)
		{
			try
			{
				if (input.Length == "ddHHmmHammerMMMyyyy".Length &&
					input.Split(
						new string[] {"Hammer"},
						StringSplitOptions.RemoveEmptyEntries
					).Length == 2
				)
				{
					DateTime returnDateTime;
					if (DateTime.TryParseExact(
						input,
						"ddHHmm'Hammer'MMMyyyy",
						CultureInfo.CurrentCulture,
						DateTimeStyles.None,
						out returnDateTime)
					)
					{
						return returnDateTime;
					}
				}
			}
			catch
			{
				// ignored
			}
			return default(DateTime);
		}
	}
}

However, if your .Net target is less than 3.5, you may not be able to compile. This is where the attribute declaration is required.

Add the following declaration to your project, either in a new .cs file or at the bottom of the extensions file:

namespace System.Runtime.CompilerServices
 {
     [AttributeUsageAttribute(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Method)]
     public class ExtensionAttribute : Attribute
     {
     }
 }

Assuming this was the only thing preventing the project from compiling, extension methods should now be available. Also, you can now use the defined extension methods as follows:

using Extensions;

namespace SampleApplication
{
    class Program
    {
		static int Main(string[] args)
		{
			DateTime originalDateTime = DateTime.Now;
			string str = originalDateTime.ToHammerTimeString();
			Console.WriteLine(str);

			DateTime newDateTimeObject = originalDateTime.CreateFromHammerTimeString(str);
			return 0;
		}
    }
}