union type is EVIL EVIL EVIL

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: # Set this to turn on the use of the union type, which gets you improved # type checking of Lisp_Objects -- they're declared as unions instead of # ints, and so places where a Lisp_Object is mistakenly passed to a routine # expecting an int (or vice-versa), or a check is written `if (foo)' # instead of `if (!NILP (foo))', will be flagged as errors. (All of these # do NOT lead to the expected results! Qnil is not represented as 0 [so if # (foo) will *ALWAYS* be true for a Lisp_Object], and the representation of # an integer as a Lisp_Object is not just the integer's numeric value, but # usually 2x the integer +/- 1.) # There used to be a claim that it simplified debugging. There may have # been a grain of truth to this pre-19.8, when there was no lrecord type # and all objects had a separate type appearing in the tag. Nowadays, # however, there is no debugging gain, and in fact frequent debugging *LOSS*, # since many debuggers don't handle unions very well, and usually there is # no way to directly specify a union from a debugging prompt. # Furthermore, release builds should *NOT* be done this way because (a) you # may get less efficiency, with compilers that can't figure out how to # optimize the union into a machine word; (b) even worse, the union type # often triggers compiler bugs, especially when combined with Mule and # error-checking. This has been the case with various times using GCC, # *AND CURRENTLY HAPPENS WITH VC++*, at least when using pdump. Therefore, # be warned! USE_UNION_TYPE=0 you might want to modify the text in the last paragraph to add something like "and also currently happens with GCC in combination with Mule, pdump, and KKCC [no error checking]. ben ----- Original Message ----- From: "Adam Duck" <duck(a)informatik.uni-frankfurt.de&gt; To: "Ben Wing" <ben(a)666.com&gt; Cc: <xemacs-beta(a)xemacs.org&gt; Sent: Monday, December 16, 2002 8:32 AM Subject: Re: crash while using calc