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=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_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 B8E5A20248 for ; Tue, 2 Apr 2019 16:17:41 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 9F3891216C2; Wed, 3 Apr 2019 01:17:34 +0900 (JST) Received: from o1678916x28.outbound-mail.sendgrid.net (o1678916x28.outbound-mail.sendgrid.net [167.89.16.28]) by neon.ruby-lang.org (Postfix) with ESMTPS id 0BE221216AD for ; Wed, 3 Apr 2019 01:17:31 +0900 (JST) Received: by filter0113p3las1.sendgrid.net with SMTP id filter0113p3las1-11097-5CA389C8-23 2019-04-02 16:11:52.417130908 +0000 UTC m=+344776.518825125 Received: from herokuapp.com (unknown [54.147.237.187]) by ismtpd0045p1mdw1.sendgrid.net (SG) with ESMTP id Cr0n-ZrsQF--9trRUYvfDQ for ; Tue, 02 Apr 2019 16:11:52.274 +0000 (UTC) Date: Tue, 02 Apr 2019 16:11:52 +0000 (UTC) From: lisa.ugray@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 67595 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 13683 X-Redmine-Issue-Author: dnagir X-Redmine-Sender: lugray 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?bs2OZptonkuqZvb0NzZ=2Fv7B=2FMKDyvM5khmKxSL9NEH9aBjgTt2v66JZzYrqvmZ?= =?us-ascii?Q?xEveAvGE0pRDzlMG3dcvHgQ4k1k1qeqZ+oh+gTp?= =?us-ascii?Q?lYdSxdyg01UbDdyjp9cPj5U5AKbYsdmCZSeUbz5?= =?us-ascii?Q?5ftoOhaV9ia=2F1kpCZR2uOFQqg3mgArKk2t5iTuR?= =?us-ascii?Q?WP3WAqaV1+tvgZdUD7QQhuazX8YBaqj5tAw=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 92111 Subject: [ruby-core:92111] [Ruby trunk 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 lugray (Lisa Ugray). I was pointed here after sharing the following code with my team mates. I really like the idea, and find I often reach for it. What about the name `only`? ``` ruby module Enumerable def only only! rescue IndexError nil end def only! raise(IndexError, "Count (#{count}) is not 1") if count != 1 first end end ``` ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-77438 * Author: dnagir (Dmytrii Nagirniak) * Status: Feedback * Priority: Normal * Assignee: * Target version: ---------------------------------------- ### 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/