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.