From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS4713 221.184.0.0/13 X-Spam-Status: No, score=-3.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_MED,RP_MATCHES_RCVD,SPF_PASS,T_DKIM_INVALID shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from neon.ruby-lang.org (neon.ruby-lang.org [221.186.184.75]) by dcvr.yhbt.net (Postfix) with ESMTP id 99BFC2082F for ; Tue, 27 Jun 2017 23:19:59 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id E6E05120814; Wed, 28 Jun 2017 08:19:57 +0900 (JST) Received: from o1678948x4.outbound-mail.sendgrid.net (o1678948x4.outbound-mail.sendgrid.net [167.89.48.4]) by neon.ruby-lang.org (Postfix) with ESMTPS id 05A3B120739 for ; Wed, 28 Jun 2017 08:19:55 +0900 (JST) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d=sendgrid.me; h=from:to:references:subject:mime-version:content-type:content-transfer-encoding:list-id; s=smtpapi; bh=BhGOArih91hfd+Il5k5+sbnCG2U=; b=GA58uoBkd2cEcmG24N xAzu6SXxC/6PBrm+7rgPK+ukR87uh9rgWzqmt0Qh3FPgPuoOQvNN3fdCRq9PkNJq XJRdJqf82jCtzgOUfDBI/fx4fJNEBx8ZQeyZUPSGuazhFlOrTxxF4XReKb5uQ6VW RpApBxG5Slh7iVxKOm8vLKMdk= Received: by filter1151p1mdw1.sendgrid.net with SMTP id filter1151p1mdw1-32179-5952E819-2 2017-06-27 23:19:53.036832438 +0000 UTC Received: from herokuapp.com (ec2-54-226-155-143.compute-1.amazonaws.com [54.226.155.143]) by ismtpd0005p1iad1.sendgrid.net (SG) with ESMTP id kzQFiG-SSQaLTsiNXCj6bw Tue, 27 Jun 2017 23:19:52.992 +0000 (UTC) Date: Tue, 27 Jun 2017 23:19:52 +0000 From: mame@ruby-lang.org To: ruby-core@ruby-lang.org Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 56822 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 13683 X-Redmine-Issue-Author: dnagir X-Redmine-Sender: mame 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: ync6xU2WACa70kv/Ymy4QrNMhiuLXJG8OTL2vJD1yS4DtuWoRSposaGC4QxigqLP2/x/9YZIznGJpp ELj0vO7Q5sNx6EHRhO0gYEZDmyfsVpOloWf9R8+JY/HKYiou5HJ80CxMFPJFN3ufsXpBuZdT+jL/LB HkIdNzu6+wzV5lXmt9tBmJZ1uEUZxPxlXZQ0BCO41jypixQbX7F5Zogrpg== X-ML-Name: ruby-core X-Mail-Count: 81796 Subject: [ruby-core:81796] [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 mame (Yusuke Endoh). +1. I always feel uncomfortable whenever using `first` for this purpose. ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-65491 * Author: dnagir (Dmytrii Nagirniak) * Status: Open * 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/