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-Status: No, score=-4.1 required=3.0 tests=AWL,BAYES_00, 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 0A4521F4B4 for ; Fri, 2 Oct 2020 14:15:03 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 4CA97120A1A; Fri, 2 Oct 2020 23:14:25 +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 346AF120A12 for ; Fri, 2 Oct 2020 23:14:22 +0900 (JST) Received: by filterdrecv-p3iad2-df8579867-7t5qf with SMTP id filterdrecv-p3iad2-df8579867-7t5qf-20-5F7735DF-B0 2020-10-02 14:14:55.945443499 +0000 UTC m=+922586.208839060 Received: from herokuapp.com (unknown) by ismtpd0036p1mdw1.sendgrid.net (SG) with ESMTP id R8L3JqULQCm0h1KCFOYl-A for ; Fri, 02 Oct 2020 14:14:55.799 +0000 (UTC) Date: Fri, 02 Oct 2020 14:14:55 +0000 (UTC) From: nobu@ruby-lang.org Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 76121 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Feature X-Redmine-Issue-Id: 13683 X-Redmine-Issue-Author: dnagir X-Redmine-Sender: nobu 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?q8Dly+pU2+3ektTtZVXgZtbJPXwqo7p86jCsvYTW4Bxab5wZ4Yu77ezFE2jZWP?= =?us-ascii?Q?FHHHsETgjR4KvvQJQ0PeoXbiK5b8myj3fWaPq7a?= =?us-ascii?Q?IaGplxnsxE2zsdFb432OJJ67E0xJ4oVZYmc=2FC0B?= =?us-ascii?Q?Qsc6YN1frbcxEx4OL83p4WaoWkzvIe3zqYap3gR?= =?us-ascii?Q?06D2I3xr7O7kQqAp1SAZPkaNOmKnFRl+UoaYHSG?= =?us-ascii?Q?NpbzNrcANhG1jmO6E=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 100280 Subject: [ruby-core:100280] [Ruby master Feature#13683] Add strict Enumerable#single 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 #13683 has been updated by nobu (Nobuyoshi Nakada). What about pattern matching? ```ruby case []; in [a]; p a; end #=> NoMatchingPatternError ([]) case [1]; in [a]; p a; end #=> 1 case [1,2]; in [a]; p a; end #=> NoMatchingPatternError ([1, 2]) ``` ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-87866 * Author: dnagir (Dmytrii Nagirniak) * Status: Feedback * Priority: Normal ---------------------------------------- ### Summary This is inspired by other languages and frameworks, such as LINQ's [Single](https://msdn.microsoft.com/en-us/library/bb155325%28v=vs.110%29.aspx) (pardon MSDN reference), which has very big distinction between `first` and `single` element of a collection. - `first` normally returns the top element, and the developer assumes there could be many; - `single` returns one and only one element, and it is an error if there are none or more than one. We, in Ruby world, very often write `fetch_by('something').first` assuming there's only one element that can be returned there. But in majority of the cases, we really want a `single` element. The problems with using `first` in this case: - developer needs to explicitly double check the result isn't `nil` - in case of corrupted data (more than one item returned), it will never be noticed `Enumerable#single` addresses those problems in a very strong and specific way that may save the world by simply switching from `first` to `single`. ### Other information - we may come with a better internal implementation (than `self.map`) - better name could be used, maybe `only` is better, or a bang version? - re-consider the "block" implementation in favour of a separate method (`single!`, `single_or { 'default' }`) The original implementation is on the ActiveSupport https://github.com/rails/rails/pull/26206 But it was suggested to discuss the possibility of adding it to Ruby which would be amazing. -- https://bugs.ruby-lang.org/