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=-2.8 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_MED,RP_MATCHES_RCVD,SPF_PASS, T_DKIM_INVALID shortcircuit=no autolearn=no 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 A17D2201A0 for ; Fri, 30 Jun 2017 13:58:09 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 87815120739; Fri, 30 Jun 2017 22:58:06 +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 64A40120730 for ; Fri, 30 Jun 2017 22:58:03 +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=34FreDoKdkjJ5TQDYaaq3JIj/6E=; b=o+npNgdf0ONOJEB0u5 bWY+TS3FAdzdtGggzmx8Uik4FR3PF1nm/XBPU10UcRMx4YE0UlCAPzF4/TcbuAaV B+lWQc3MAjHlYGceATB6Sgg/W5Y7SQsAxRE/Jkb9INi1YLd5nz+ioeXJ/KigLaWa mJh0Oj92sMpg4bn09DnzvfWmM= Received: by filter1106p1mdw1.sendgrid.net with SMTP id filter1106p1mdw1-20489-595658E7-D 2017-06-30 13:57:59.054470605 +0000 UTC Received: from herokuapp.com (ec2-54-158-194-247.compute-1.amazonaws.com [54.158.194.247]) by ismtpd0029p1mdw1.sendgrid.net (SG) with ESMTP id f3sArjzuTc2FNgAU6ofYpA Fri, 30 Jun 2017 13:57:59.010 +0000 (UTC) Date: Fri, 30 Jun 2017 13:57:59 +0000 (UTC) From: dnagir@gmail.com To: ruby-core@ruby-lang.org Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 56905 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 13683 X-Redmine-Issue-Author: dnagir X-Redmine-Sender: dnagir 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/Ymy4QrNMhiuLXJG8OTL2vJD1yS5l+Dwjvq1ULfpyWTJDL4iuE4ccDJzzfE4Sc5 eMGHp9rfmbTyssoMEtw/tqUNIL+HbcCqYEiAVFIhWX3YZUHQGOjfXMvgwFT+kG3jlQiksD59DtUnn9 3W8ggWEMeQTEN66W0KtBgMK0m24RIq18LaPh X-ML-Name: ruby-core X-Mail-Count: 81874 Subject: [ruby-core:81874] [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 dnagir (Dmytrii Nagirniak). shevegen (Robert A. Heiler) wrote: > What would the results be for the following code? I would expect the following: ```ruby [].single # => error [1].single # =>1 [1,2].single # => error [1,2,3].single # => error {}.single # => error {cat: 'Tom'}.single # same as .first => [:cat, 'Tom'] {cat: 'Tom', mouse: 'Jerry'}.single # error ``` ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-65603 * 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/