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 0D00A1F4B4 for ; Fri, 25 Sep 2020 07:12:35 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id E348D120AEE; Fri, 25 Sep 2020 16:11:56 +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 7E51C120ABB for ; Fri, 25 Sep 2020 16:11:55 +0900 (JST) Received: by filterdrecv-p3mdw1-canary-6f8d794f68-zsjd2 with SMTP id filterdrecv-p3mdw1-canary-6f8d794f68-zsjd2-19-5F6D985B-42 2020-09-25 07:12:27.822536923 +0000 UTC m=+292437.683056147 Received: from herokuapp.com (unknown) by ismtpd0101p1iad2.sendgrid.net (SG) with ESMTP id vmwc7JR4RzyJV4r3rJJV_w for ; Fri, 25 Sep 2020 07:12:27.770 +0000 (UTC) Date: Fri, 25 Sep 2020 07:12:27 +0000 (UTC) From: nobu@ruby-lang.org Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 75968 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+3ektTtZVXgZtbJPXwqo7p86jCsvYTW4BxjbaPmpLJcKTP2NaDJ8=2F?= =?us-ascii?Q?7sSv6=2FuvAaxUxG9epAOkNecxjo4B93sW98qIeaS?= =?us-ascii?Q?IU1+V0R892EDvXXBkM5XSINMvl9VtZU3m+Ds0kk?= =?us-ascii?Q?XgG=2FzzJiDj8Ora9JXhM4Hh2SUmPxyRYMRGlsRD5?= =?us-ascii?Q?4kx4+lpY8Iv0uDMr9mt3V7pdENOhc0sNcxaig8K?= =?us-ascii?Q?oWccrRPxRgLloUoC4=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 100128 Subject: [ruby-core:100128] [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). Dan0042 (Daniel DeLorme) wrote in #note-25: > > If collection is empty and a block was given, returns the block's return value: > > I really think the block form should be like find/select > > ```ruby > [1,2,3].one{ _1.even? } #=> 2 > [1,2,3,4].one{ _1.even? } #=> error > [1,2,3,4].one(nil){ _1.even? } #=> nil > ``` It looks close to `Enumerable#one?` which counts truthy values only, but has a different semantics. ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-87697 * 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/