Marc Nieper-Wißkirchen wrote:
> The existing protocol is as follows:
>
> Hamt_entry *e = hamt_entry (...);
> Hamt_entry *p = e;
> Hamt *new_hamt = hamt_insert (old_hamt, &p);
> if (old_hamt == new_hamt)
> {
> /* The element hasn't been insert as an equivalent element has already
> been in the hamt. p now holds a reference to the entry that already existed
> in the hamt.
> element_free (e);
> ...
> hamt_free (old_hamt); /* We don't have to free new_hamt because no new
> hamt was created. */
> }
> else
> {
> /* The element has been inserted. p hasn't changed. */
> ...
> hamt_free (old_hamt); /* This frees all hamts */
> hamt_free (new_hamt); /* and all elements inserted, including e. */
> }
>
> A protocol where no pointer values need to be compared could use p to
> carry the information:
>
> Hamt_entry *e = hamt_entry ();
> Hamt_entry *p = e;
> Hamt new_hamt = hamt_insert (old_hamt, &p);
> if (p == e)
> {
> /* The element has been inserted. */
> ... /* See above. */
> }
> else if (p == NULL)
> {
> /* The element e already existed in the hamt. */
> ... /* See above. */
> }
> else /* p != e && p != NULL */
> {
> /* An element equivalent to e already existed in the hamt. p now holds
> this element. */
> ... /* See above. */
> }
I find the latter protocol more robust: it does not depend on details of
the implementation of hamt_insert.
Can you decide on your original question (allow stack-allocated HAMTs)?
I don't feel I can help you decide this.
Bruno
