4.3 Delegates Versus Interfaces

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 IFilter interface:

using System;
interface IFilter {
   bool Filter(string s);
}
class Test {
  class FirstHalfOfAlphabetFilter : IFilter {
    public bool Filter(string s) {
      return ("N".CompareTo(s) > 0);
    }      
  }
  static void Main( ) {
    FirstHalfOfAlphabetFilter f = new FirstHalfOfAlphabetFilter( );
    Display(new string [ ] {"Ant", "Lion", "Yak"}, f);
  }
  static void Display(string[ ] names, IFilter f) {
    int count = 0;
    foreach (string s in names)
      if (f.Filter(s))
        Console.WriteLine("Item {0} is {1}", count++, s);
  }
}

In this case, the problem is slightly more elegantly handled with a delegate, but generally delegates are best used for event handling.