Another colleague brought me present today – the blog post. Thank you. You were right!

We will do some refactoring which will lead us from Anti-Pattern to Pattern. From Sequential Coupling to Template Method. And as I see it could be very common way to refactor bad code that represents mentioned anti-pattern.

So, lets start with the following question. What do you see to be wrong with following code?

  public class Manager
  {
    public void DoTheProject()
    {
      IWorker worker = GetMeWorker();
      worker.PreWork();
      worker.Work();
   
  worker.AfterWork();
    }

Manager is very angry guy and he needs to get the project done. For that he would like to get some worker, which implements IWorker interface, and delegate some work to him. But also manager knows that worker could be new to project so it will require do go ahead and to some preparational work before and maybe something to do after work is done…

What is wrong? Answer is that Manager cares too much about how worker should organize his work. Why should manager know that worker needs to be prepared for work? What do we have here is the Sequential Coupling anti-pattern.

(My definition) 

Sequential Coupling Anti-Pattern – appears when consuming code is forced to call methods of used object in particular sequence to make it work correctly.

If we call Work and then PreWork, code could be broken. And we want to prevent this. For example, we can move all that stuff in one method – Work, but also sometimes it is needed to perform pre or/and after work, but sometimes not. That is why we had following design that allowed us do this. See that StandardWorker doesn’t need do something after he has finished. This was achieved with virtual and abstract methods.

  public interface IWorker
  {
    void
PreWork();
    void
Work();
    void
AfterWork();
  }
  public abstract class
WorkerBase : IWorker
  {
    public
virtual void
PreWork(){}
   
public abstract
void Work();
    public
virtual void
AfterWork(){}
  }
  public class StandardWorker : WorkerBase
  {
    public override
void PreWork()
    {
      Console.WriteLine(“… I need to prepare to work …”);
    }
    public
override void
Work()
    {
     
Console.WriteLine(“… hard work is in process …”);
    }
  }

So, what we need to do is to hide the order in which we call methods, be sure that order remains the same, and still have possibility to override each of method. What I just described is Template Method.

In our example we could leave one method in interface, then implement it in base class with calling everything else we need in correct order, each of those things we call could be overridden, we left them protected to do not show to the world.

  public interface IWorker
  {
    void Work();
  }
  public abstract class
WorkerBase : IWorker
  {
    
    //this is template method
    public
void Work()
    {
      PreWorkActivity();
      WorkActivity();
   
  AfterWorkActivity();
    }
    protected virtual
void PreWorkActivity() { }
    protected abstract void
WorkActivity();
    protected virtual void AfterWorkActivity() { }
  }
  public class StandardWorker : WorkerBase
  {
    protected override
void PreWorkActivity()
    {
      Console.WriteLine(“… I need to prepare to work …”);
    }
    protected override
void WorkActivity()
    {
      Console.WriteLine(“… hard work is in process …”);
    }
  }
  public class Manager
  {
    public
void DoTheProject()
    {
      IWorker worker = GetMeWorker();
      worker.Work();
    }
    private IWorker GetMeWorker()
    {
      return new
StandardWorker();
    }
  }

It really looks for me that it could be common to perform refactoring from Sequential Coupling to Template Method. Hope you liked this post.

If you haven't subsribed yet, you can subsribe below: