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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Message #14 received at 50219 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Eric Abrahamsen <eric <at> ericabrahamsen.net>
Cc: Lars Ingebrigtsen <larsi <at> gnus.org>, 50219 <at> debbugs.gnu.org
Subject: Re: bug#50219: 28.0.50; Provide better errors when trying to
 specialize on optional args in generic methods
Date: Sat, 28 Aug 2021 10:15:17 -0400

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)) ...)


-- Stefan

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