RE: Re: union type is EVIL EVIL EVIL

it's useful to compile with union type to catch problems, as stephen mentions, but it has such a propensity to create random crashes due to compiler bugs, which often appear like xemacs problems, that people who don't have a good idea of its uses should not use it. it's similar with c++ but there are other advantages ... for example my recently-introduced bad-gcpro-catching code. note also that it's possible to catch insufficient gcproing using c++, but somewhat difficult. i put in a comment to this effect in my kkcc patch. ben ------- Original Message ------- On Tue, 17 Dec 2002 22:35:11 +0900 Stephen J. Turnbull?wrote: >>>>> "Ville" == Ville Skytt <Ville> writes: Ville> On Tue, 2002-12-17 at 04:20, Ben Wing wrote: >> stephen -- while you're in the process of modifying PROBLEMS, >> please add an entry about union type and its propensity to >> cause crashes. here's some text that should get you started: Ville> [...] Ville> Uh, --use-union-type has been many times suggested on Ville> xemacs-beta as a way to prevent crashes in something Ville> related to aggressive compiler Ville> What's correct? To some extent, both. Sometimes you lose, and other times you lose big. There's nothing we can do about compiler bugs except write them up in PROBLEMS and code defensively. There are any number of temporaries in XEmacs notated with "Compiler XYZ chokes without this." This is more of the same. :-( To me it's a pragmatic issue (if anything, union type is more "righteous" than the int Lisp_Object type). GCC (and now VC++) has historically had problems with unions.[1] OTOH unions have historically been good at smoking out "if (lisp_object) ..." constructs and the like, and to some extent aliasing issues. I think if you look, you'll find that (a) it's often been me recommending union type[2] and (b) --use-union-type typically doesn't solve any problems. If better diagnosis tools are now available, then there may be reason to avoid union type. Footnotes: [1] They've also had problems with std C++ ... but I doubt Ben would argue that is EVIL EVIL EVIL ;-) [2] Ie, you're really only citing one opinion. -- Institute of Policy and Planning Sciences http://turnbull.sk.tsukuba.ac.jp University of Tsukuba Tennodai 1-1-1 Tsukuba 305-8573 JAPAN Ask not how you can "do" free software business; ask what your business can "do for" free software.