Re: Non-opaque hamt type?

[Marc Nieper-Wißkirchen]

Okay, if you find the latter protocol better anyway, I will switch to
this protocol, and hamts will be stack-allocated (just two words) and
passed by value.

Thanks,

Marc

Am So., 18. Okt. 2020 um 19:58 Uhr schrieb Bruno Haible <bruno@clisp.org>:
>
> 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
>