Re: Is there utility in making hash-table-{keys, values} built-in functions?

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Shankar Rao <shankar.rao@gmail.com> writes:

> This isn't about syntax, as changing hash-table-{keys,values} to be
> built-in functions wouldn't change their syntax.
>
> I was curious about this because there doesn't seem to be a way to
> iterate over a hash-table without either explicitly or implicitly
> using a lambda. For example, if we macro expand the following cl-loop

Yes, I understood that, and I thought maybe you were asking this because
you were annoyed by having to write a lambda and so on, which using
cl-loop would avoid.

>
> (cl-loop for key being hash-keys of tables using (hash-values v)
>          collect (func k v))
>
> we obtain:
>
> (cl-block nil
>   (cl-block --cl-finish--
>     (maphash
>      (lambda
>        (key v)
>        (func k v))
>      tables))
>   nil)
>
> Most languages that provide a hash-table data structure provide
> methods for directly accessing the hash keys and values. I'm trying to
> understand if it would be beneficial for elisp to provide these as
> well. Would it provide a significant enough speed boost for code that
> frequently iterates over hash keys/values? Is there some complication
> implementing these functions in C directly?

I think Matthias said something like that already: It would be consing
up lists, that we otherwise don't need, and that's far from free.

My own gut feeling is that it might well be more expensive than maphash,
depending on the hash table size, of course. The least I would say is
that it's not a clear win.