Re: Is there a way of setting a variable only when it exists?

[Marcin Borkowski]

On 2022-03-14, at 14:48, Emanuel Berg via Users list for the GNU Emacs text 
editor <help-gnu-emacs@gnu.org> wrote:

> Stefan Monnier via Users list for the GNU Emacs text editor wrote:
>
>>> I assume it would be fairly easy to code such a macro
>>> (using `boundp'), but maybe it exists already?
>>
>> AFAIK it doesn't exist yet. The reason for it is that it is
>> not often useful. Typically there are two cases:
>>
>> - If the var exist, you want to set it and if not you have
>>   no fallback. In that case, it is typically harmless to set
>>   the var even when it doesn't exist, so the code just uses
>>   `setq` without bothering to test `boundp`.
>>
>> - If the var exist you want to set it, and if it doesn't you
>>   want to do something else. In that case, the something
>>   else tends to depend on the specifics so (if (boundp 'foo)
>>   (setq foo ..) ...) is about s good as it gets.
>
> If it exists set it with `setq'. If it doesn't exist, create
> and set it ... with `setq'?

What if it's an internal Emacs variable which might become a user option
one day (I submitted a bug report about it) and then my customization
silently disappears?  It's the "silently" part I want to guard
against...

Best,

-- 
Marcin Borkowski
http://mbork.pl