bug#73505: EIEIO manual out of date, doesn't reflect current functionality

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 26 Sep 2024 22:45:27 +0000
> From:  zyd via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> The info manual for EIEIO seems to be out of date, specifically the introduction
> section:
> 
>     (info "(eieio) Introduction")
> 
> Therein it's stated that EIEIO lacks support for both eql specializers and
> `:around' methods
> 
> 
> > EQL specialization
> >    EIEIO does not support it.
> > 
> > ‘:around’ method tag
> >      This CLOS method tag is non-functional.
> 
> 
> But this isn't true at all, EIEIO has both of these features fully functional in
> fact. 
> 
> -------------------------------------------------------------------------------
> 
> (cl-defgeneric inform-chat (msg preamble))
> 
> (cl-defmethod inform-chat (msg (preamble (eql :night)))
>   (message "Good night chat, %s" msg))
> 
> (cl-defmethod inform-chat (msg (preamble (eql :morning)))
>   (message "Good morning chat, %s" msg))
> 
> (inform-chat "that's all she wrote. What more do you want from me?" :night)
> ;; => "Good night chat, that's all she wrote. What more do you want from me?"
> 
> (inform-chat "many mornings such as this one, today is different! Today is the day I tell you all my hot takes." :morning)
> ;; => "Good morning chat, many mornings such as this one, but today is the day I
> ;; tell you all my hot takes."
> 
> (cl-defmethod inform-chat :around (msg (preamble (eql :morning)))
>   (setq msg (concat "even though there are " msg " Now I know, I know... you're sick of them but I must. I'm compelled, even!"))
>   (cl-call-next-method msg preamble))
> 
> (inform-chat "many mornings such as this one, today is different! Today is the day I tell you all my hot takes." :morning)
> ;; => "Good morning chat, even though there are many mornings such as this one,
> ;; today is different! Today is the day I tell you all my hot takes. Now I know,
> ;; I know... you're sick of them but I must. I'm compelled, even!"
> 
> -------------------------------------------------------------------------------
> 
> So I wonder, how much of the rest of the manual is out of date like this? Is it
> not to be trusted as a source of factual information about the current state of
> CLOS in elisp?

You are using above cl-defgeneric and cl-defmethod, which are not part
of EIEIO.  So I think the EIEIO manual is not mistaken in what it
says.  But maybe I'm missing something.  Adding Stefan who might have
comments.