Extension Methods

Sınıfın yapısını değiştirmeden sınıfa ek olarak yazılabilen fonksiyonlardır.

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 static methods, but they’re called as if they were instance methods on the extended type.

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/extension-methods

The following example shows an extension method defined for the System.String class. It’s defined inside a non-nested, non-generic static class:

namespace ExtensionMethods
{
    public static class MyExtensions
    {
        public static int WordCount(this string str)
        {
            return str.Split(new char[] { ' ', '.', '?' },
                             StringSplitOptions.RemoveEmptyEntries).Length;
        }
    }
}