What are the Extension Methods in C#?

Extension methods enable you to add methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. 

An extension method is a special kind of static method, but they are called as if they were instance methods on the extended type.

Benefits of extension methods

• Extension methods allow existing classes to be extended without relying on inheritance or having to change the class's source code.
• If the class is sealed than there in no concept of extending its functionality. For this a new concept is introduced, in other words extension methods.
• This feature is important for all developers, especially if you would like to use the dynamism of the C# enhancements in your class's design.

Important points for the use of extension methods:

• An extension method must be defined in a top-level static class.
• An extension method with the same name and signature as an instance method will not be called.
• Extension methods cannot be used to override existing methods.
• The concept of extension methods cannot be applied to fields, properties or events.
• Overuse of extension methods is not a good style of programming.