"Debug only" code that should run only when "turned on"

Question

I would like to add some C# "debug only" code that only runs if the person debugging requests it. In C++, I used to do something similar to the following:

void foo()
{   
  // ...
  #ifdef DEBUG
  static bool s_bDoDebugOnlyCode = false;
  if (s_bDoDebugOnlyCode)
  {
      // Debug only code here gets executed when the person debugging 
      // manually sets the bool above to true.  It then stays for the rest
      // of the session until they set it to false.
  }
  #endif
 // ...
}

I can't do exactly the same in C# since there is no local statics.

Question: What is the best way to accomplish this in C#?

1. Should I use a private class static field with C# preprocessor directives (#if/#endif DEBUG)?
2. Should I use the Conditional attribute (to hold the code), and then a private class static field (not surrounded by C# preprocessor directives #if/#endif DEBUG?).
3. Something else?

Answer 1

An instance variable would probably be the way to do what you want. You could make it static to persist the same value for the life of the program (or thread depending on your static memory model), or make it an ordinary instance var to control it over the life of an object instance. If that instance is a singleton, they'll behave the same way.

#if DEBUG
private /*static*/ bool s_bDoDebugOnlyCode = false;
#endif

void foo()
{   
  // ...
#if DEBUG
  if (s_bDoDebugOnlyCode)
  {
      // Code here gets executed only when compiled with the DEBUG constant, 
      // and when the person debugging manually sets the bool above to true.  
      // It then stays for the rest of the session until they set it to false.
  }
#endif
 // ...
}

Just to be complete, pragmas (preprocessor directives) are considered a bit of a kludge to use to control program flow. .NET has a built-in answer for half of this problem, using the "Conditional" attribute.

private /*static*/ bool doDebugOnlyCode = false; 
[Conditional("DEBUG")]
void foo()
{   
  // ...    
  if (doDebugOnlyCode)
  {
      // Code here gets executed only when compiled with the DEBUG constant, 
      // and when the person debugging manually sets the bool above to true.  
      // It then stays for the rest of the session until they set it to false.
  }    
  // ...
}

No pragmas, much cleaner. The downside is that Conditional can only be applied to methods, so you'll have to deal with a boolean variable that doesn't do anything in a release build. As the variable exists solely to be toggled from the VS execution host, and in a release build its value doesn't matter, it's pretty harmless.