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

[Drew Adams <drew.adams@oracle.com>]

> I don't think a unified conversion interface is that important.
> The various structures used for mappings are just too different.
> For example, alists and plists aren't real types, they are only
> defined by their usage. Hash tables, on the other hand, are real
> types, with a per-object comparison function, a non-nil empty
> value, etc. These two kinds of objects are just too different
> to treat uniformly. Also, in most cases it is statically known
> which kinds of objects are involved, so a generic function that
> dynamically selects on the type of object isn't that useful.
>
> How about adding some simple conversion functions to subr.el such as
> 
> (defun alist-to-hashtable (alist &rest keys) ...) 
> (defun hashtable-to-alist (hashtable) ...)

Which brings us back to the very first msg of this thread -
the bug report.  Please see the code I proposed there.

And note the differences from the signature you show for
`alist-to-hashtable'.  I think those differences are
important and your signature is not satisfactory.