On Friday, March 02, 2012 16:19:13 deadalnix wrote: > Le 02/03/2012 15:37, Jacob Carlborg a écrit : > > On 2012-03-02 14:00, deadalnix wrote: > >> Le 02/03/2012 05:51, Jonathan M Davis a écrit : > >>> On Friday, March 02, 2012 05:37:46 Nathan M. Swan wrote: > >>>> Am I correct that trying to use an Object null results in > >>>> undefined behavior? > >>>> > >>>> Object o = null; > >>>> o.opCmp(new Object); // segmentation fault on my OSX machine > >>>> > >>>> This seems a bit non-D-ish to me, as other bugs like this throw > >>>> Errors (e.g. RangeError). > >>>> > >>>> It would be nice if it would throw a NullPointerError or > >>>> something like that, because I spent a long time trying to find a > >>>> bug that crashed the program before writeln-debugging statements > >>>> could be flushed. > >>> > >>> It's defined. The operating system protects you. You get a segfault on > >>> *nix and > >>> an access violation on Windows. Walter's take on it is that there is > >>> no point > >>> in checking for what the operating system is already checking for - > >>> especially > >>> when it adds additional overhead. Plenty of folks disagree, but that's > >>> the way > >>> it is. > >> > >> The assertion that it has overhead isn't true.You'll find solutions > >> without overhead (using libsigsegv in druntime for example). > >> > >> BTW, object should be non nullable by default, if you ask me. The > >> drawback of null is way bigger than any benefit. > > > > Isn't it quite unsafe to throw an exception in a signal ? > > The signal handler is called on top of the stack, but the information to > retrieve the stack trace are system dependant. BTW, using lib like > libsigsegv can help a lot to make it safe. It isn't safe ATM, but it is > doable.
You could definitely set it up to print a stack trace in the signal handler on at least some systems, but throwing an exception would _not_ be a good idea. So, a NullPointerException _would_ require additional overhead, because it would require checking the pointer/reference for null every time that you dereference it. Of course, it wouldn't work if anyone installed their own signal handler, so using a signal handler has its limits anyway, but it could be done. - Jonathan M Davis
