bug#28753: 25.3; Functions to get alist from hash table and vice versa

[Noam Postavsky <npostavs@users.sourceforge.net>]

On Thu, Oct 12, 2017 at 9:27 AM, Nicolas Petton <nicolas@petton.fr> wrote:
> Michael Heerdegen <michael_heerdegen@web.de> writes:
>
>>> Actually, going from alist to hash table doesn't look so
>>> useful with `map-into'.  A caller should be able to specify
>>> the hash-table parameters (features), such as :test.
>>
>> Yeah, that's what I thought, too.
>
> That's something I can easily add.  `map-into' would then look like
> the following `(defun map-into (map type &rest keywords))'.
>
> However, `keywords' would be ignored when converting to an alist.  I'm
> not sure I like it.

What about just receiving the hash-table as a parameter:

(defun map-into (map type)
  "Convert the map MAP into a map of type TYPE.

TYPE can be one of the following symbols: `list', `hash-table'; or it
can be a hash-table to use.
MAP can be a list, hash-table or array."
  (pcase type
    (`list (map-pairs map))
    (`hash-table (map--into-hash-table map))
    ((pred hash-tablep) (map--into-existing-hash-table map type)
    (_ (error "Not a map type name: %S" type)))))

(defun map--into-existing-hash-table (map hash-table)
  ...)