Why we use “this” in Extension Methods?

Question

I want to ask why we use \"this\" keyword before the parameter in an extension method (C# Language)........... like this function :

    public static int ToI         


        

Answer 1

Mainly because it is how the C# spec defines an extension method. See Section 10.6.9

10.6.9 Extension methods

When the first parameter of a method includes the this modifier, that method is said to be an extension method. Extension methods can only be declared in non-generic, non-nested static classes. The first parameter of an extension method can have no modifiers other than this, and the parameter type cannot be a pointer type.