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 E33E81F8C1 for ; Thu, 7 May 2020 07:24:02 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id D7B4C120A67; Thu, 7 May 2020 16:23:38 +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 92183120A4B for ; Thu, 7 May 2020 16:23:37 +0900 (JST) Received: by filter0084p3las1.sendgrid.net with SMTP id filter0084p3las1-1974-5EB3B78D-63 2020-05-07 07:23:57.372869029 +0000 UTC m=+1848129.510376030 Received: from herokuapp.com (unknown) by ismtpd0016p1iad2.sendgrid.net (SG) with ESMTP id Zj86B6y8Tp2wO9mKAe-sSg for ; Thu, 07 May 2020 07:23:57.224 +0000 (UTC) Date: Thu, 07 May 2020 07:23:57 +0000 (UTC) From: ko1@atdot.net Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 73932 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: ko1 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?fVTMYOBjtdvXNcWwrscBhLsHItUXVK5L4mtnq0mdcRe5sY6Tr+YPwYrt2Pdl29?= =?us-ascii?Q?0aEBxSnSw0VoaCjbTSnmOPPrbInkUTmlZFQ6a=2Fh?= =?us-ascii?Q?PrBsBLz6dgLlw8Sb65A595pZjPCtrH4jAuoaLDh?= =?us-ascii?Q?PLZjO563mLPqOFZhLdOaArUZb0j98xGq9kb0K0k?= =?us-ascii?Q?bps6sPcGLY8qG?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 98171 Subject: [ruby-core:98171] [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 ko1 (Koichi Sasada). Eregon (Benoit Daloze) wrote in #note-14: > Much like all Enumerable methods return `Array` and (of course) do not copy instance variables, I think Array methods should do the same. +1 ---------------------------------------- Bug #6087: How should inherited methods deal with return values of their own subclass? https://bugs.ruby-lang.org/issues/6087#change-85409 * 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/