I've been reading about the tradeoffs between different iteration methods,
and the consensus seems to be that dolist, dotimes, and cl-loop are more
efficient than mapc and seq-do, because the former methods macro-expand (in
almost all cases) to a while loop, while the latter require a lambda, which
are generally slower and harder to debug.

I see what you're saying that allocating a list of keys just to iterate
once over a hash table would be wasteful. And I suppose it also wouldn't
make sense to have a built-in just for iterating over hash-tables.

Shankar Rao

On Thu, Nov 28, 2024 at 6:31 PM Mattias Engdegård <
mattias.engdegard@gmail.com> wrote:

> 28 nov. 2024 kl. 12.53 skrev Shankar Rao <shankar.rao@gmail.com>:
>
> > I noticed that the functions hash-table-keys and hash-table-values are
> just wrappers around maphash. This means that there is no way to iterate
> over a hash-table without using a lambda.
> >
> > Would it be useful or worthwhile to implement these directly in C? I
> don't know much about low-level Emacs development, but having these as
> built-ins could make iteration of a hash-table a little faster and easier
> to debug.
>
> It's unlikely that it would be faster to make a list just for the purpose
> of a single iteration; the allocation costs alone would be too high. Other
> ways of iterating through hash-tables have been tried with mostly
> disappointing results, although there might be some value in avoiding use
> of the C stack in some cases.
>
> If you tell us what you are trying to accomplish, it would be easier for
> us to help you.
>
>