Re: HAMT iterator

[Bruno Haible]

Marc Nieper-Wißkirchen wrote:
> > > 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).

Whether copying an iterator can be done by assignment or requires a function
call, is of second importance.

The more important point I wanted to make: Does allocating an iterator
require a (heap) memory allocation?

If you iterate with do_while, no memory allocation is needed, because all
information is stored on the stack, between the various function calls.

If you iterate with hamt_iterator_create, and the Hamt_iterator type
has bounded size (I guess it will not require more than 15 pointers and
13 indices), it can be stored on the caller's stack.

Bruno