Why extension method are static in c#

 In C#, when a class or method is marked as static, it means they belong to the type itself rather than to instances of that type. Here are the reasons why extension methods and classes are static in C#:

1. Static Nature of Extensions: Extension methods allow you to add new methods to existing types without modifying those types. To achieve this, extension methods must be defined as static methods in a static class. This is because they are called as if they were instance methods of the extended type, but they are actually just static methods that receive the extended type instance as their first parameter.

2. Syntax and Usage: The static keyword is used to define methods and classes that are not tied to instance-specific data but rather operate on types themselves or on specific instances passed as parameters. Extension methods need to be static because they are intended to be invoked as if they were instance methods on the extended type.

3. Design and Intent: By making extension methods and classes static, C# enforces a clear separation between instance methods (which operate on specific object instances) and extension methods (which provide additional functionality to existing types without inheritance or modification of those types).

For example, consider a simple extension method that adds functionality to the String class:

public static class StringExtensions
{
    public static bool IsCapitalized(this string str)
    {
        if (string.IsNullOrEmpty(str))
            return false;

        return char.IsUpper(str[0]);
    }
}

Here, StringExtensions is a static class containing a static method IsCapitalized, which extends the string type with additional functionality. This design ensures clarity and consistency in how extension methods are defined and used in C#.