What is an extension method in C#?

Extension Method - is a static method that can be called as if it were a method of the extended type, although it is actually defined outside of that type.

Main features:

• It is a static method declared in a static class.
• The first parameter of the extension method must be marked with the this keyword and indicate the type you want to extend.
• Extension methods do not have access to private and protected members of the extended type.
• They allow adding functionality to existing types without modifying their source code or using inheritance.

Example of creation and usage:

1. Defining a static class and a static extension method:

   public static class StringExtensions // Static class
   {
       public static string ToTitleCase(this string input) // Extension method for string type
       {
           if (string.IsNullOrEmpty(input))
           {
               return input;
           }
           // Simple logic to convert to Title Case
           return System.Globalization.CultureInfo.CurrentCulture.TextInfo.ToTitleCase(input.ToLower());
       }
   }
   

2. Using the extension method:

   string myString = "hello world";
   string titleCaseString = myString.ToTitleCase(); // Called as if it were a regular string method
   // titleCaseString now contains "Hello World"