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Lambdas and anonymous delegates for Debugging

  • Artigo

I was posed the problem a few weeks ago that someone has a coding project where the execution engine swallows all exceptions and unless explicitly catching all exceptions (he didn’t want to put a big try catch around everything in production code) there would be little or difficulty in finding if an exception had been thrown in one of his modules.

After some thought, I considered that by utilising anonymous delegates (Action and Func) he would be able to add testing to the existing code very easily, and utilize the Debug/Release modes within Visual Studio.

I proposed, unfortunately with out use of whiteboards or anything which would have been useful, to have within a test harness a helper method which took one of these anonymous delegates, and caught all exceptions and wrote them to Trace to allow him to view them after a test. 

 public static void ExceptionHelper(Action action)
 {
     try
     {
         action();
     }
     catch (Exception ex)
     {
         Trace.WriteLine(ex);
     }
 }

Within the main body of the test harness to add an

 #if DEBUG

to allow him to easily swap between running with exceptions handled himself or to allow them to pass through to the execution engine.

 public static void TestHarness()
 {
     Trace.Listeners.Add(new ConsoleTraceListener());
 #if DEBUG
     ExceptionHelper(FunctionToTest);            
 #else
     FunctionToTest();
 #endif
 }

Now when Visual Studio runs the test harness in Debug mode, the exceptions will be caught, as the delegate points to the FunctionToTest method which is executed by the action(); line in ExceptionHelper.  If the user is in Release mode (i.e. not in Debug) then the Function will be executed as normal.

Comments

  • Anonymous
    February 17, 2010
    Don't forgot to add throw; after the Trace.WriteLine call. Also in your example you're not actually using an anonymous delegate. If FunctionToTest took a parameter you could find yourself swimming in overloads of ExceptionHelper. I tend to call these like: ExceptionHelper( () => FunctionToTest() );

  • Anonymous
    February 17, 2010
    Thanks Josh, I considered doing the call like this but reverted back to this for readability, though I totally agree with you that this would make calling parameterised functions far simpler. Thanks, Dave