Why is the exception a class and not a structure?

• An exception is a single piece of information.
• Exceptions are (or should be) by definition rare cases in the life of an application, so boxing, unpacking and copying is not a problem I guess.
• Exceptions are almost always outside the scope they were thrown from, so there is a risk of having an exception reference stored somewhere, making it a good candidate to advance to the next generation of GC, whereas structures are easier to clean up.
• Immutable Struct is thread safe.

• You never want the exception to be null (even the compiler or the CLR forces you to do this, try something below):

  throw null;
  
        
  
          
          
          
        
  
      

  then you get:

  NullReferenceException
  
        
  
          
          
          
        
  
      

Is there any specific reason why exceptions are classes?