Re: Scheme style auto-resizing hashtable (fwd)

[hjstein@bfr.co.il (Harvey J. Stein)]

Jay Glascoe <jglascoe@jay.giss.nasa.gov> writes:

 > > Of these three approaches, the iterator approach would be more memory
 > > efficient, but probably a mess otherwise.
 > 
 > actually, hash->alist would give you a list of pairs.  These pairs would
 > be the same objects as the pairs in the hash table, so creating the list
 > wouldn't use up much memory at all.  It's also probably the fastest
 > approach (you'd only call hash->alist once: BANG! it's done.  whereas with
 > an iterator, you'd wind up calling it many times (bang!, bang!, bang!...). 

Calling what many times?  What's wrong with this:

(define (hashtable-foreach h f)
   (do ((i 0 (1+ i))
        (n (hashtable-length h))
        (v (hashtable-vector h)))
       ((i >= n))
     (for-each (lambda (data) (apply f (cdr data)))
               (vector-ref v i))))

hash->alist (aka hashtable->list) still has to cons up the list that
points to all the pairs in the hashtable, so it's still a lot of
garbage - 1 cons cell for each object in the hash table.

-- 
Harvey J. Stein
BFM Financial Research
hjstein@bfr.co.il