Advanced C# - Delegates Versus Interfaces

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A problem that can be solved with a delegate can also be solved with an interface. For instance, the following explains how to solve our filter problem using an ITransformer interface:

  public interface ITransformer
  {
    int Transform (int x);
  }

  public class Util
  {
   public static void TransformAll (int[] values, ITransformer t)
   {
     for (int i = 0; i < values.Length; i++)
       values[i] = t.Transform(values[i]);
   }
  }

  class Test : ITransformer
  {
   static void Main()
   {
     int[] values = new int[] {1, 2, 3};
     Util.TransformAll(values, new Test());
     foreach (int i in values)
       Console.WriteLine (i);
   }

   public int Transform (int x) { return x * x; }
  }

A delegate design may be a better choice than an interface design if one or more of these conditions are true:

1. The interface defines only a single method.
   
2. Multicast capability is needed.
   
3. The listener needs to implement the interface multiple times.

In theITransformerexample, we don’t need to multicast. However, the interface defines only a single method. Furthermore, our listener may need to implementITransformermultiple times, to support different transforms, such as square or cube. With interfaces, we’re forced into writing a separate type per transform, sinceTestcan only implementITransformeronce. This is quite cumbersome:

  class Test

  {
   static void Main()
   {
     int[] values = new int[] {1, 2, 3};
     Util.TransformAll(values, new Cuber());
     foreach (int i in values)
       Console.WriteLine (i);
   }

   class Squarer : ITransformer
   {
     public int Transform (int x) { return x * x; }
   }
   class Cuber : ITransformer
   {
     public int Transform (int x) {return x * x * x; }
   }
  }

Please check back next week for the continuation of this article.

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