GNU bug report logs - #50219
28.0.50; Provide better errors when trying to specialize on optional args in generic methods

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From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: Eric Abrahamsen <eric <at> ericabrahamsen.net>, 50219 <at> debbugs.gnu.org
Subject: bug#50219: 28.0.50; Provide better errors when trying to specialize on optional args in generic methods
Date: Sat, 28 Aug 2021 18:02:40 +0200

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

> Eric Abrahamsen [2021-08-26 18:31:44] wrote:
>> (cl-defmethod testy ((arg1 string) &optional (arg2 integer))
>>   (message "Don't do this"))
> [...]
>> Warning: reference to free variable 'integer'
>
> Hmm....
>
> The same thing happens in Common-Lisp, tho.  What's going on here is
> that the arglist of `cl-defmethod` allows Common-Lisp style arguments
> (e.g. `&key`) so your `(arg2 integer)` means to use `integer` as the
> default value for `arg2`, just as in
>
>     (cl-defun testy (arg1 &optional (arg2 integer)) ...)

Hm...  So the warning here is correct, I guess.  But perhaps it could
also have said something about it being ambiguous syntax (since is also
knows the declared parameter list from `cl-defgeneric')...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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