TurtleSoft posted on the Interest list earlier about problems we had with exception handling, and Thiago suggested I post here.
Since the early 90s, our C++ code has had about 10,000 sanity checks which give an error message with source file & line number, then throw an exception. There is a try/catch block in the event loop which swallows them. That way users can continue work. Only a small % of the checks are ever called, but it makes bugs very easy to fix when users or testers report them. Our app almost never crashes thanks to the many checks. We learned the system from Bill Atkinson, author of MacPaint and HyperCard. The sanity system started in Metrowerks PowerPlant, then worked OK in Carbon, Cocoa, and MFC. For Qt we wrapped QApplication::notify with try/catch. It worked for most checks on Macintel and Wintel, but failed for Mac ARM. After the message, instant termination. Users lose their work, testers must start over. Turns out that Qt intentionally does not support exceptions thrown through GUI classes, and the early success was just an accident. Exceptions are an "exceptionally" handy C++ feature. Instant "beam me up, Scotty". It is too bad that Qt does not support them fully, and I'd like to change that. So I would be willing to work on getting GUI classes like QWidget able to pass exceptions, if it means we can get our old sanity-checking back. It would be our open-source contribution. I realize this is a huge, fundamental change to Qt. It would need to be a multi-year project, done in tiny bits so as not to break things. Anyhow, my time is limited. Getting exceptions through signals/slots is lower priority. We don't use those much and probably could bypass them somehow. We just want a reliable path to the event loop. Personally, I've programmed since punch card days in 1966 or so. I've designed and shipped several apps for PCs. I've refactored and rebuilt all sorts of C++ code from other people, and could do this work politely and competently. Does this seem reasonable? Dennis Kolva Programming Director TurtleSoft.com
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