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=-2.8 required=3.0 tests=AWL,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_PASS shortcircuit=no autolearn=no 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 53C6B1F463 for ; Tue, 24 Sep 2019 13:21:18 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 1E0CD1209C1; Tue, 24 Sep 2019 22:21:04 +0900 (JST) Received: from xtrwkhkc.outbound-mail.sendgrid.net (xtrwkhkc.outbound-mail.sendgrid.net [167.89.16.28]) by neon.ruby-lang.org (Postfix) with ESMTPS id A873F120969 for ; Tue, 24 Sep 2019 22:21:00 +0900 (JST) Received: by filter0129p3las1.sendgrid.net with SMTP id filter0129p3las1-3594-5D8A183E-4A 2019-09-24 13:21:02.340358363 +0000 UTC m=+65443.452466326 Received: from herokuapp.com (unknown [54.157.43.252]) by ismtpd0003p1iad1.sendgrid.net (SG) with ESMTP id 8Ax6wOwmROeBxeSqHrYRlA for ; Tue, 24 Sep 2019 13:21:02.223 +0000 (UTC) Date: Tue, 24 Sep 2019 13:21:02 +0000 (UTC) From: eregontp@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 70611 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 16178 X-Redmine-Issue-Author: Eregon X-Redmine-Issue-Assignee: Eregon X-Redmine-Sender: Eregon 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?KippOI8ZHtTweq7XfQzW93937kJ4QNWwSBuHnaMEcr2KZAp5wS043eQtAFpyQB?= =?us-ascii?Q?8uG0FZnzhWMD69WtkAjJ3j=2Fojov6n5AoDlpqMeA?= =?us-ascii?Q?q5yCa26mMgI1jCr5H0Sh89SPpx636ivhy64l39i?= =?us-ascii?Q?zDWJEDMID1B2gj=2Fk=2FrtIKjoUgwKAdUb7gct9XXc?= =?us-ascii?Q?OxvdqlzuFKPQwmCHFPgCjlBU+CkM1NqLKVw=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 95056 Subject: [ruby-core:95056] [Ruby master Bug#16178] Numbered parameters: _1 should be the same as |x| and _0 should not exist 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 #16178 has been reported by Eregon (Benoit Daloze). ---------------------------------------- Bug #16178: Numbered parameters: _1 should be the same as |x| and _0 should not exist https://bugs.ruby-lang.org/issues/16178 * Author: Eregon (Benoit Daloze) * Status: Open * Priority: Normal * Assignee: Eregon (Benoit Daloze) * Target version: * ruby -v: ruby 2.7.0dev (2019-09-24T12:57:54Z master 0e84eecc17) [x86_64-linux] * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN ---------------------------------------- Currently on trunk: ```ruby array = ["string", 42, [1, 2]] array.map { |x| x * 2 } # => ["stringstring", 84, [1, 2, 1, 2]] array.map { _1 * 2 } # => ["stringstring", 84, 2] ``` Oops, this trivial code just lost data and completely ignored the element class! This is clearly contrary to intuition and is very dangerous. Using `_0` instead has the correct behavior but it's clear we use 1-based indexing for numbered parameters, and it doesn't solve that `_1` has dangerous behavior. Basically the current behavior is that `_0` is the same as `|x|` and `_1` is the same as `|x,|`. `|x,|` is almost never used in Ruby, and for good reasons, it just throws away data/information/the class of the object. Such a dangerous operation should only be done when it's explicit, and the trailing comma in `|x,|` shows that, but `_1` does not. So let's make `_1` be `|x|` and remove `_0`. I am going to be harsh, but this discussion has gone too long without any serious written argument for the current behavior: I believe it's irrational and irresponsible to have `_1` be `|x,|`, it's just going to lead to nasty bugs. Try to convince me otherwise. If not, in one week I want to apply this change. >From the discussion in https://bugs.ruby-lang.org/issues/15723#note-127 and in https://bugs.ruby-lang.org/issues/15708 -- https://bugs.ruby-lang.org/