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=-3.9 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS 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 D57EA1F463 for ; Wed, 25 Sep 2019 11:55:02 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 4A4B9120B5A; Wed, 25 Sep 2019 20:54:53 +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 B1A2E120B58 for ; Wed, 25 Sep 2019 20:54:50 +0900 (JST) Received: by filter0100p3las1.sendgrid.net with SMTP id filter0100p3las1-26499-5D8B558A-1C 2019-09-25 11:54:50.300252245 +0000 UTC m=+146121.819315717 Received: from herokuapp.com (unknown [184.73.122.220]) by ismtpd0027p1mdw1.sendgrid.net (SG) with ESMTP id XoB0HEF5TJOSVoTbzoZ37g for ; Wed, 25 Sep 2019 11:54:50.102 +0000 (UTC) Date: Wed, 25 Sep 2019 11:54:50 +0000 (UTC) From: ko1@atdot.net Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 70640 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 16178 X-Redmine-Issue-Author: Eregon 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?fVTMYOBjtdvXNcWwrscBhLsHItUXVK5L4mtnq0mdcRd1i0=2F0DVoCWsL0PQXTeL?= =?us-ascii?Q?7zabWClO18Ui2=2FSOey9HrAWapkraFvm6TS04bi0?= =?us-ascii?Q?hA0Had2AX5lrqHKOUxw7NWdNostN=2FvPjqPi9dPy?= =?us-ascii?Q?lnWKSdYCweLP570CuH9s9Wp9aW7furbQ7KRrgrD?= =?us-ascii?Q?j2XoGCtjxnTro?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 95085 Subject: [ruby-core:95085] [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 updated by ko1 (Koichi Sasada). > Beautifully simple: > _0 is a single implicit parameter, as in x in { |x| } > _1 is the first numbered parameter, as in x in { |x,y,z,etc| } > _2 is the second numbered parameter, as in y in { |x,y,z,etc| } I think `_0` and `_1` are very confusing because people can consider it is sequential meaning. However, the meaning is different. It is same as `$0` and `$1`, but they are completely different feature (program name and regexp). `_0` and `_1` is very confusing. This proposal also introduces inconsistency, but it is better than `_0` and `_1` idea, I think. > Of course, having _ as the only unnamed parameter would have |x| semantics, > but I guess it's too late for that and now we have _ parameters. Completely agreed (and I like `<>` for `|e|` and `` for `_n` :p, but rejected this notation). ---------------------------------------- Bug #16178: Numbered parameters: _1 should be the same as |x| and _0 should not exist https://bugs.ruby-lang.org/issues/16178#change-81717 * Author: Eregon (Benoit Daloze) * Status: Closed * Priority: Normal * Assignee: matz (Yukihiro Matsumoto) * 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 Some reactions to this behavior in https://twitter.com/eregontp/status/1115318993299083265 -- https://bugs.ruby-lang.org/