Re: Two questions about generalized variables

[Michael Heerdegen <michael_heerdegen@web.de>]

Eric Abrahamsen <eric@ericabrahamsen.net> writes:

> I didn't mean symbol property lists! Just the plain old '(:key1 "value1"
> :key2 "value2") kind. They're useful for a few different things -- in
> this case, initializing class instances.

Oh, I see.  Hmm, one could define a place expander quite similarly to
the one of `alist-get', I think, but it doesn't seem one to be
predefined, indeed.


> >> The second question is setting hashtable entries. Right now I have code
> >> like this:
> >>
> >> (setf (gethash uuid my-hashtable)
> >>       (append (list (list 'thingone 'thingtwo))
> >>               (gethash uuid my-hashtable)))
> >
> > Isn't that more or less `push'?
>
> I started off with `push', but the code in question doesn't know if the
> key exists or not, and you can't push to nil.

The gv setter is calculated using the (unevaluated) place expression, so
"pushing to nil" doesn't happen.  See the gv-expander of `alist-get' for
example, which of course also works for nonexistent keys.


Regards,

Michael.