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=-2.6 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,UNPARSEABLE_RELAY 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 6E4F81F4B4 for ; Tue, 15 Sep 2020 06:35:56 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 6E2D91208FC; Tue, 15 Sep 2020 15:35:19 +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 AD96F1208F9 for ; Tue, 15 Sep 2020 15:35:16 +0900 (JST) Received: by filterdrecv-p3las1-c5988c487-cqsv5 with SMTP id filterdrecv-p3las1-c5988c487-cqsv5-18-5F6060C3-7 2020-09-15 06:35:47.228793107 +0000 UTC m=+387441.143387870 Received: from herokuapp.com (unknown) by ismtpd0033p1iad2.sendgrid.net (SG) with ESMTP id JnX6B9oFR9-BU3aHdl070w for ; Tue, 15 Sep 2020 06:35:47.081 +0000 (UTC) Date: Tue, 15 Sep 2020 06:35:47 +0000 (UTC) From: shannonskipper@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 75848 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Feature X-Redmine-Issue-Id: 13683 X-Redmine-Issue-Author: dnagir X-Redmine-Sender: shan 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?T0jc+HUEV7CM5SiK=2FBdwdf6zPPpzUxEkATeka3QtAYo3=2F31HunPP=2FIXSkNUmYV?= =?us-ascii?Q?xIsS5WsAzqvTmHkm7rk3mgOydDSU=2F7bz3fQOszl?= =?us-ascii?Q?ZFmaK6FzGC+eDr8=2FZqfYbzZMYT45GvaHkyaISTf?= =?us-ascii?Q?rYXPb9BfR4YYRD9C5wuImpqnMsG04Svu=2FNqO7my?= =?us-ascii?Q?5c9n2virXNQEffM1q72x=2Fj9Zb0CMMMgTOVipFG1?= =?us-ascii?Q?DEZXH6kobSmaVHEpc=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 100008 Subject: [ruby-core:100008] [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 shan (Shannon Skipper). How about #sole since it means one and only and is concise? ``` ruby [].sole #!> SoleError: empty Array when single value expected (contains 0, expected 1) Set.new.sole #!> SoleError: empty Set when single value expected (contains 0, expected 1) [41, 42, 43].sole #!> SoleError: too many values in Array when just one expected (contains 3, expected 1) [42].sole #=> 42 ``` Or #one_and_only, but it's more wordy. ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-87559 * 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/