Hi, While doing the recent retagging work I realized that I really wanted to kill weak pairs. They look like pairs but you can't actually access their fields using car and cdr -- terrible things. To do that I had to reimplement the weak hash tables, to make them not use them. I did that, reimplementing them as open-addressed hash tables, with robin hood linear probing on collision. It seems to work well. Besides the performance improvement you get with just scanning linearly through memory, open-addressed hash tables aren't structurally perturbed by the disappearing links. It's a lot less messy, and uses less memory, and we have space to encode the actual hash values in the table. (However I don't think our current hash functions are very good.)
The one nasty thing there was adapting to the old interfaces. In particular the hashx interface expects to be able to assoc down a list, but there are no assoc lists in the new weak tables. Guess what I do? That's right, for weak hashx tables I make new association lists in the equal? handler, then pass that alist to the user's assoc function. Gross. Currently the new weak tables are only accessible under the old API. I don't know whether to publicise the new API, or make a different API, or what. If we hadn't coded the handle API into our hash tables I would replace the regular (strong) hash table implementation too. I might still do that but it's not pressing. Anyway, thoughts on the API are welcome. Regards, Andy ps. The new weak tables are thread-safe. Yay. -- http://wingolog.org/
