The Decorator Pattern & Extension Methods in c#

Question

Before going to describe my problem first,I would like to define definitions of Decorator and Extension method Decorator

Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality

Extension method

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

I have following code snippet in c#

public interface IMyInterface {     void Print(); }  public static class Extension {     public static void PrintInt(this IMyInterface myInterface, int i)     {         Console.WriteLine             ("Extension.PrintInt(this IMyInterface myInterface, int i)");     }      public static void PrintString(this IMyInterface myInterface, string s)     {         Console.WriteLine             ("Extension.PrintString(this IMyInterface myInterface, string s)");     } }  public class Imp : IMyInterface {     #region IMyInterface Members      public void Print()     {         Console.WriteLine("Imp");     }      #endregion }  class Program {     static void Main(string[] args)     {         Imp obj = new Imp();         obj.Print();         obj.PrintInt(10);     } } 

In the above code I am extending interface without modifying the existing code,and these two methods are available to derived class. So my question is this: Is the extension method a replacement of the decorator pattern?

Answer 1

A extension method is really just syntactic sugar for calling a static method.

While with a decorator you could actually change the behaviour of your decorated class, a extension method could only alter properties or call methods on your class, just like an "ordinary" static method.

Decorator pattern is actually definied as using a wrapper to alter behaviour, which a extension method clearly doesn't do.