Monday, March 29, 2010

Remove unused code

When considering the next set of FxCop rules to enable on the build server, my first thought was to look at those dealing with properly disposing of objects. Scanning the active projects at work has revealed a rule-set slightly more important - unused code. In some of our older code bases there are a variety of methods, variables, etc. that are no longer being used. Deleting the dead code will make it easier to understand what the code is actually doing. In many cases, this will also fix a variety of other FxCop issues, as the flagged items are no longer present. Why fix what you will eventually delete?

And before I go over the rules I should emphasize deletion of dead code. I've seen numerous instances where a developer has commented out, #ifdef'd, or otherwise excluded a section of code. In some cases this was to finish or re-implement the code later. In other cases it was to remove code not currently needed. Regardless, this should be avoided. Tracking previous revisions of code is what source control is for.

The first rule to address is Avoid uninstantiated internal classes. This is a class not visible outside the assembly and is never actually used within that assembly. If you're lucky, deleting this class will improve a variety of code metrics (the number of FxCop warnings being just one of them.)

For the next examples I reference the following class:

    9   public class Unused

   10   {

   11       int unusedPrivateField;


   13       private void UnusedPrivateCode()

   14       {

   15           Debug.WriteLine("This method isn't called");

   16       }


   18       internal void DoWork()

   19       {

   20           int unusedLocal;

   21           Debug.WriteLine("This is the only method possibly called");

   22       }

   23   }

Working through the code, line 11 returns a warning for the rule Avoid unused private fields. Notice that none of the methods use it and it isn't exposed through a property.

Next, the method UnusedPrivateCode violates, you guessed it, Avoid uncalled private code. This method is uncalled locally and unreachable outside the class.

The final violation is of type Remove unused locals, at line 20. The variable is not used within the method and can be removed. Note that this rule will also fire if the variable is assigned to, but its value is never actually used. An example:

   18   public void DoWork()

   19   {

   20       int unusedLocal = 0;

   21       unusedLocal = 12; // Still not using...

   22   }

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