Outro exemplo de Extension Methods no C#

Program.cs

using System

public class ProcessFile
{
	public static void Main()
	{
		string s1 = "Good morning dear students";
		Console.WriteLine(s1.Cut(0));
	}
}

StringExtensions.cs

namespace System

static class StringExtensions
{
	public static string Cut(this string thisObj, int count)
	{
		if(thisObj.Lenght <= count)
		{
			return thisObj;
		}
		else
		{
			return thisObj.Substring(0, count) + "...";
		}
	}
}