From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.help Subject: Re: EIEIO: A question about interfaces Date: Thu, 14 Jan 2021 12:47:39 -0500 Message-ID: References: <877dofee8e.fsf@web.de> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="26465"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:s4FAfBf1MRLbweM5qc3+57IgZyw= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Thu Jan 14 19:35:04 2021 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1l07SZ-0006mI-RH for geh-help-gnu-emacs@m.gmane-mx.org; Thu, 14 Jan 2021 19:35:03 +0100 Original-Received: from localhost ([::1]:55890 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l07SY-00045p-Ry for geh-help-gnu-emacs@m.gmane-mx.org; Thu, 14 Jan 2021 13:35:02 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:36102) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l06is-0001vy-K8 for help-gnu-emacs@gnu.org; Thu, 14 Jan 2021 12:47:56 -0500 Original-Received: from ciao.gmane.io ([116.202.254.214]:44494) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l06ir-0006WS-2B for help-gnu-emacs@gnu.org; Thu, 14 Jan 2021 12:47:50 -0500 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1l06io-00015G-2M for help-gnu-emacs@gnu.org; Thu, 14 Jan 2021 18:47:46 +0100 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.248, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:127243 Archived-At: [ Side note; I'm a functional programmer, so OO design is not something I'm good at. Also, while I am familiar with the CLOS features and semantics, I don't have much experience using it. ] > Now I want to allow that some objects of some of these classes have/ > support an additional feature. I think the idea is that those objects which support that extra feature aren't really of the same type as those that don't, so you'd create a new class for them. In your example, that might mean you'd create a new class that inherits from both `my-1` and `my-foo-interface`. Of course, another approach is to not use the OO approach to solve this problem but instead to use good'ol `if` tests, tho you'll still need to store that `additional` info somewhere: you could add some `extra-properties` to all your objects and store it there, tho depending on the specifics there are likely to be various other options. Stefan