Re: Hash-table elements

[pjb@informatimago.com (Pascal J. Bourguignon)]

Nordlöw <per.nordlow@gmail.com> writes:

> Can hash-tables contain references other "global" structures?
>
> I have a hash-table that maps filenames to their metadata,file-scan-
> hits/misses.
> I don't want to pull-change-push the whole meta-data value whenever I
> change parts of these metadata/hits.
>
> Is this possible somehow?

Yes.  Only do not modify the keys!  You wouldn't be able to retrieve
them, since changing the state of a key would probably change its hash
value, and therefore the bucket where the hash-table stored it.
But you can do whatever you want on the value.

(require 'cl)
(let ((h (make-hash-table)))

   (let ((value (list 1 2 3))
         (key   :my-list))

      (setf (gethash key h) value)
      (setf (car value) 0
            (cdr value) 'z)
      (gethash key h)))
--> (0 . z)

     
-- 
__Pascal Bourguignon__