Question

I’m following a tutorial on MVC on the .NET 4 framework. The tutorial created a function like this…

using System.Web;
using System.Web.Mvc;

namespace vohministries.Helpers
{
    public static class HtmlHelpers
    {
        public static string Truncate(this HtmlHelper helper, string input, int length)
        {
            if (input.Length <= length)
            {
                return input;
            }
            else
            {
                return input.Substring(0, length) + "...";
            }
        }
    }
}

I have no idea whatthis HtmlHelper helper means or represents in the function argument. Is this something new in .NET 4? I think it may be extending the HtmlHelper class but I’m not sure…Could someone explain the syntax?

Answer 1

It’s an extension method. (Been in since C# 3.0):

Extension methods enable you to “add”
methods to existing types without
creating a new derived type,
recompiling, or otherwise modifying
the original type. Extension methods
are a special kind of static method,
but they are called as if they were
instance methods on the extended type.
For client code written in C# and
Visual Basic, there is no apparent
difference between calling an
extension method and the methods that
are actually defined in a type.