c# - combine 2 statements in a catch block into one

Question

Does anybody know if it's possible to write the code in the catch block below as a single statement? I haven't been able to come up with a way, and was just curious if there was one.

IMPORTANT: the stack trace must be preserved.

    catch (Exception e)
    {
        if (e is MyCustomException)
        {
            // throw original exception
            throw;
        }

        // create custom exception
        MyCustomException e2 =
            new MyCustomException(
                "An error occurred performing the calculation.", e);
        throw e2;
    }

Answer 1

catch (Exception e)
{
   if (e is MyCustomException) throw;

   throw new MyCustomException("An error occurred performing the calculation.", e);
}

I think that's about as terse as it gets, I think.

This immediately throws MyCustomException up the stack (which is what you're accomplishing with throw; in your question) while throwing a MyCustomException to wrap other Exception types encountered in execution.

Alternatively, you can just do:

catch (Exception e)
{
   throw new MyCustomException("An error occurred performing the calculation.", e);
}

and in the case where MyCustomException was caught, you'll have a MyCustomException in e.InnerException where is e a MyCustomException at the next level of the stack OR you'll have a System.Exception in the cases that MyCustomException is not what was caught.

Answer 2

catch (Exception e)
{
    throw !e is MyCustomException ? throw new MyCustomException("message", e) : e;
}

This will shrink it down but it essentially does the same thing.

Doh... no, this will definitely not work. hmm... you still end up with your code, or an inverted version with an else, but that's redundant.

Answer 3

What about:

catch (MyCustomException)
{
   throw;
}
catch (Exception ex)
{
   throw new MyCustomException(ex);
}

Answer 4

I know that this isn't answering your original question, however its worth noting that you should be careful when using throw - although miles better than throw ex, there may still be circumstances where using throw does not preserve the stack trace. See:

http://weblogs.asp.net/fmarguerie/archive/2008/01/02/rethrowing-exceptions-and-preserving-the-full-call-stack-trace.aspx

Answer 5

It is actually possible.

However, the stacktrace will contain additional entries:

public static class ExceptionHelper
{
    public static void Wrap<TException>(Action action, Func<Exception, TException> exceptionCallback)
        where TException : Exception
    {
        try
        {
            action();
        }
        catch (TException)
        {
            throw;
        }
        catch (Exception ex)
        {
            throw exceptionCallback(ex);
        }
    }
}
//Usage:
ExceptionHelper.Wrap(() => this.Foo(), inner => new MyCustomException("Message", inner));

Answer 6

Would this work?

        catch (Exception e)
        {
            throw e.GetType() == typeof(MyCustomException) ? e : new MyCustomException("An error occurred performing the calculation.", e);
        }