title: Using marker classes to control logic flow
body: <p>I have been going through some code seen that a colleague of mine is using 'marker classes' to control program logic (see contrived example below). It seems to work well, and the code reads really nicely, but there is just something about it that smells...</p>
  
  <pre><code>namespace ConsoleApplication4983
  {
      public class MyClass
      {
          static void Main()
          {
              var c = new MyClass();
              c.DoSomething(new Sequential());
              c.DoSomething(new Random());
          }
  
          public void DoSomething(ProcessingMethod method)
          {
              if (method is Sequential)
              {
                  // do something sequential
              }
              else if (method is Random)
              {
                  // do something random
              }
          }
      }
  
      public class ProcessingMethod {}
      public class Sequential : ProcessingMethod {}
      public class Random : ProcessingMethod {}
  }
  </code></pre>
  
  <p>What would be a better way of achieving the same effect? Enums? Attributes?</p>