Re: HAMT iterator

[Marc Nieper-Wißkirchen]

Am So., 11. Okt. 2020 um 13:02 Uhr schrieb Bruno Haible <bruno@clisp.org>:
>
> Hi Marc,
>
> > I am going to implement the following iterator API as well:
> >
> > /* An alternative interface to iterating through the entry of a hamt
> >    that does not make use of a higher-order function like
> >    hamt_do_while uses the opaque Hamt_iterator type.  */
> > typedef struct hamt_iterator Hamt_iterator;
> >
> > /* Return a newly created iterator for HAMT.  */
> > extern Hamt_iterator *hamt_iterator_create (const Hamt *hamt);
>
> The pointer return here is overkill. A prototype
>
>   extern Hamt_iterator hamt_iterator_create (const Hamt *hamt);
>
> is sufficient, because the way such an iterator is used is:
>
>   Hamt_iterator iter = hamt_iterator_create (hamt);
>
>   for (...)
>     {
>       ...
>       Hamt_entry *elt;
>       if (hamt_iterator_next (&iter, &elt))
>         {
>           ...
>         }
>       ...
>     }
>
>   hamt_iterator_free (&iter);
>
> > /* Return an independent copy of ITER that is initially in the same
> >    state.  */
> > extern Hamt_iterator *hamt_iterator_copy (Hamt_iterator *iter);
>
> Then a copy function is not needed, because the user's program can do
>
>   Hamt_iterator iter_clone = iter;

The hamt itself has to be copied (to increase the reference counter).

> > /* Return true if ITER is not at the end, place the current element in
> >    *ELT_PTR and move the iterator forward.  Otherwise, return
> >    *false.  */
> > extern bool hamt_iterator_next (Hamt_iterator *iter,
> >                                 Hamt_entry *const *elt_ptr);
>
> The 'const' here forbids assigning to *ELT_PTR.

Yes. Wrong position of const.