Hi, Kevin Ryde <[EMAIL PROTECTED]> writes:
>> but their semantics are a >> little fuzzy to me. In particular, I don't understand why the size of >> the tail array can be specified in both `make-vtable-vtable' and >> `make-struct': What does that mean? > > Nosing around the code, I think make-vtable-vtable adds space to the > vtable (or rather vtable-vtable) struct like "class data". Then > make-struct adds space to a struct created from it like "instance > data". Hmm, right. >> It seems that the code is a bit unclear on this too: >> >> guile> (define v (make-vtable-vtable "pr" 0)) >> guile> (define s (make-struct v 123)) >> guile> (struct-ref s 10) >> Segmentation fault > > Digging around I think that to have a tail array you're meant to say > "pR" or "pW" or whatever at the end of the layout. Without R, W or O > then it looks like the internal func scm_struct_init doesn't > initialize the tail array contents, so then scm_struct_ref reads out > garbage as an SCM, and that can cause a segv if you attempt to print > it. Yes, ok. > Should make-struct throw an error, or should it initialize? I guess > initializing is the smallest change, but it looks like struct-set! > refuses to work in the tail part without "W" at the end, so maybe > R,W,O is how it's meant to be. Yes, `make-struct' should check the vtable's layout last field, checking whether it contains a capital letter, and throw an error if TAIL_ARRAY_SIZE is non-zero and the last layout letter is not capitalized. Once this check is added, `struct-ref' can keep blindly trusting the `n_words' thing. The layout machinery is a bit heavyweight and ought to be factorized I think. Layout info could also be compiled to a more readily usable form. Thanks, Ludovic. _______________________________________________ Guile-devel mailing list Guile-devel@gnu.org http://lists.gnu.org/mailman/listinfo/guile-devel
