Debug only methods in C#/.NET

 
In Steve Maguire's Writing Solid Code, he encourages writing Debug only code that double checks complex logic.  For example, Excel uses a highly optimized evaluation method.  In the Debug build, there is another method that evaluates the same arguments and the two results are compared to ensure that the optimizations haven't broken the intent of the code.
 
Writing Debug only code is a powerful technique, but can break the Release mode build.  For example, debug only methods are often defined as follows:
#ifdef DEBUG
private void DoDebugChecks()    {}
#endif
 
Then each call to DoDebugChecks needs to be wrapped in #ifdef blocks.  Forget one, and the release mode build breaks.  C# offers a better solution: the Conditional attribute.
 
[Conditional("DEBUG")]
private void DoDebugChecks()     {}
 
This indicates to the compiler that DoDebugChecks is only executed in builds where DEBUG is true.  The compiler automatically compiles out all references during the build.  Two comments:
  1. I wish the .NET team had provided a [DebugOnly] attribute that gives the same functionality.  I'm a stickler for compile time checks, and so I worry about someone mistyping DEBUG and creating a very hard to find defect.
  2. Debug only methods are great, but make sure they do not alter the state of the application.  Just like in Debug.Asserts, make sure there aren't any side effects, or the release build will behave differently than expected.

1 Comment

  • Thanks - I hadn't heard of that attribute before, it will be very helpful. I guess the reason they made you use "DEBUG" is because by using a string, you could block methods from executing in other build configurations too, like if you had a build configuration named "DEBUG NO SYMBOLS", etc.

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