From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS4713 221.184.0.0/13 X-Spam-Status: No, score=-3.8 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from neon.ruby-lang.org (neon.ruby-lang.org [221.186.184.75]) by dcvr.yhbt.net (Postfix) with ESMTP id 65AC01F5AD for ; Fri, 10 Apr 2020 07:18:19 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 96BAC120ADF; Fri, 10 Apr 2020 16:17:58 +0900 (JST) Received: from o1678948x4.outbound-mail.sendgrid.net (o1678948x4.outbound-mail.sendgrid.net [167.89.48.4]) by neon.ruby-lang.org (Postfix) with ESMTPS id 326CE120ADF for ; Fri, 10 Apr 2020 16:17:56 +0900 (JST) Received: by filterdrecv-p3iad2-8ddf98858-5j4tk with SMTP id filterdrecv-p3iad2-8ddf98858-5j4tk-19-5E901DB6-32 2020-04-10 07:18:14.576710402 +0000 UTC m=+1318247.647080950 Received: from herokuapp.com (unknown) by ismtpd0060p1mdw1.sendgrid.net (SG) with ESMTP id OtRiEqb5Qke0bwQQlQAyOQ for ; Fri, 10 Apr 2020 07:18:14.477 +0000 (UTC) Date: Fri, 10 Apr 2020 07:18:14 +0000 (UTC) From: matz@ruby.or.jp Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 73540 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Bug X-Redmine-Issue-Id: 6087 X-Redmine-Issue-Author: marcandre X-Redmine-Issue-Assignee: matz X-Redmine-Sender: matz X-Mailer: Redmine X-Redmine-Host: bugs.ruby-lang.org X-Redmine-Site: Ruby Issue Tracking System X-Auto-Response-Suppress: All Auto-Submitted: auto-generated X-SG-EID: =?us-ascii?Q?bXEIHGfdFwsIlBTndiToCp=2Fmc2rfxRD2sZAksRKJIHUkpz7EzDRSDPUcGQBfKH?= =?us-ascii?Q?qVJclCGAhlrAy5RaoI+ih0FiaOZdUib=2FGdPjAeU?= =?us-ascii?Q?aSJDDhC3E95O669JVdBYnnEyNmJ9ZScGYhR4Znl?= =?us-ascii?Q?2L5FfT8I5hyKpn204dP5Y1I5XCPlhywnvST2yu9?= =?us-ascii?Q?fMD=2Fje0uG4qQHa6iBM3Hp8ELOA38upQncjQ=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 97780 Subject: [ruby-core:97780] [Ruby master Bug#6087] How should inherited methods deal with return values of their own subclass? X-BeenThere: ruby-core@ruby-lang.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: Ruby developers List-Id: Ruby developers List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ruby-core-bounces@ruby-lang.org Sender: "ruby-core" Issue #6087 has been updated by matz (Yukihiro Matsumoto). Should we do an experiment in 3.0? Matz ---------------------------------------- Bug #6087: How should inherited methods deal with return values of their own subclass? https://bugs.ruby-lang.org/issues/6087#change-84996 * Author: marcandre (Marc-Andre Lafortune) * Status: Assigned * Priority: Normal * Assignee: matz (Yukihiro Matsumoto) * Target version: 3.0 * ruby -v: trunk ---------------------------------------- Just noticed that we still don't have a consistent way to handle return values: ```ruby class A < Array end a = A.new a.flatten.class # => A a.rotate.class # => Array (a * 2).class # => A (a + a).class # => Array ``` Some methods are even inconsistent depending on their arguments: ```ruby a.slice!(0, 1).class # => A a.slice!(0..0).class # => A a.slice!(0, 0).class # => Array a.slice!(1, 0).class # => Array a.slice!(1..0).class # => Array ``` Finally, there is currently no constructor nor hook called when making these new copies, so they are never properly constructed. Imagine this simplified class that relies on `@foo` holding a hash: ```ruby class A < Array def initialize(*args) super @foo = {} end def initialize_copy(orig) super @foo = @foo.dup end end a = A.new.flatten a.class # => A a.instance_variable_get(:@foo) # => nil, should never happen ``` I feel this violates object orientation. One solution is to always return the base class (`Array`/`String`/...). Another solution is to return the current subclass. To be object oriented, I feel we must do an actual `dup` of the object, including copying the instance variables, if any, and calling `initialize_copy`. Exceptions to this would be (1) explicit documentation, e.g. `Array#to_a`, or (2) methods inherited from a module (like `Enumerable` methods for `Array`). I'll be glad to fix these once there is a decision made on which way to go. -- https://bugs.ruby-lang.org/