Extension methods

Extension methods are a nice piece of syntactic sugar added to C# version 3.0 as part of .NET framework 3.5. They allow you to add methods to existing types, for example you can add a new method to the type System.String or System.IO.File.

To make an extension method, make the method static and put the this keyword in the front of the type you're extending as the first parameter, like so.

public static class ExtensionMethods
{
    public static void RemoveWhitespace(this string text)
    {
        return text.Replace(" ", "")
                   .Replace("\t", "")
                   .Replace("\n", "");
    }
}

And this is how you would call string.RemoveWhitespace

string text = " a string ";
text.RemoveWhitespace();
// text == "astring" 

Really all that is happening here is you're using a different/nicer syntax to call regular method. Instead of calling some method static string RemoveWhitespace(string text), you're calling it on the instance of string you want to modify.

Extension properties

Extension properties are among the list of features being considered for future versions of C#. Until then we'll need to make do by implementing java-style getters and setters if required.