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

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

[Shankar Rao]

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Hello all,

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.

Shankar

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

[Mattias Engdegård]

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.

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

[Gerd Möllmann]

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

> Hello all,
>
> 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.

If this is about syntax, cl-loop has support for hash tables. For
example

  for x being the hash-keys of something using (hash-value y)