Hi,
Kevin Ryde <[EMAIL PROTECTED]> writes:
> I made a bit of a start trying to improve the structures section of
> the manual, I always found it pretty hard to follow. One big
> stumbling block for me was vtables, but I now see if you want to make
> a struct you have to make a vtable vtable, and from that a vtable, and
> only then your struct. Seems hard work for casual users, if you're
> not (at first) interested in that second level of "type of type".
My understanding (which might be inaccurate) is that there is in fact no
such three-level indirection: in classic reflective OO terms,
`make-vtable-vtable' returns a "class" object which `make-struct' can
then use to return regular (i.e., non-class) objects. In particular,
this example (from `structs.test') works:
(let* ((vtable (make-vtable-vtable "pr" 0))
(s1 (make-struct vtable 0 "hello"))
(s2 (make-struct vtable 0 "hello")))
;; S1 and S2 are both "regular" one-field structs.
(equal? s1 s2))
So I think it's even more confusing than it seems. ;-)
I'd say that `make-vtable-vtable' is inappropriately named and should
really be `make-vtable'. Does that make sense?
(Not to mention that the primary use of the term "vtable" is for
_method_ pointers in C++, which definitely has nothing to do with this.)
> How about something like this to just make a vtable from fields and
> optional printer func,
>
> (define (make-vtable fields . print)
> (apply make-struct (make-vtable-vtable "" 0) 0
> (make-struct-layout fields)
> print))
IIUC, `(define make-vtable make-vtable-vtable)' should suffice.
Thanks,
Ludovic.
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