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, URIBL_BLOCKED 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 501D01F66E for ; Fri, 28 Aug 2020 20:19:17 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 76C7E120AE4; Sat, 29 Aug 2020 05:18:41 +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 2083B120ADA for ; Sat, 29 Aug 2020 05:18:39 +0900 (JST) Received: by filterdrecv-p3iad2-787bb5c9bc-9fj4x with SMTP id filterdrecv-p3iad2-787bb5c9bc-9fj4x-19-5F4966BC-85 2020-08-28 20:19:08.826324717 +0000 UTC m=+94765.375434596 Received: from herokuapp.com (unknown) by ismtpd0033p1iad2.sendgrid.net (SG) with ESMTP id WaJpqJs2T62obzg4UYYcuQ for ; Fri, 28 Aug 2020 20:19:08.762 +0000 (UTC) Date: Fri, 28 Aug 2020 20:19:08 +0000 (UTC) From: fatkodima123@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 75589 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Feature X-Redmine-Issue-Id: 13683 X-Redmine-Issue-Author: dnagir X-Redmine-Sender: fatkodima 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?RvZ0H4gD69HjmyxuoEldmMenU4znNUKl7mOsZIogdq6Q+2rhQRCxhMioXrMxC4?= =?us-ascii?Q?umq8kdVN+sAPYSXdo5doiF9VDgxv=2FGCRG=2FXUrM7?= =?us-ascii?Q?QygNdQQw2iksg+yorvRvtKPTgCO1M=2FVpY81uvAR?= =?us-ascii?Q?FId4P6WzHkWUzJgrETEjHDHC45WPP3o8jPxzLGp?= =?us-ascii?Q?6=2Fdt7fBrC58t69Xia1TBxI0KytHFxEmEsTg=2F2hW?= =?us-ascii?Q?ZnI5dPzp3c574CK6Q=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 99757 Subject: [ruby-core:99757] [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 fatkodima (Dima Fatko). I have opened a PR - https://github.com/ruby/ruby/pull/3470 ``` # Returns one and only one item. Raises an error if there are none or more than one. [99].one #=> 99 [].one #=> RuntimeError: collection is empty [99, 100].one #=> RuntimeError: collection contains more than one item # If collection is empty and no block was given, returns default value: [].one(99) #=> 99 # If collection is empty and a block was given, returns the block's return value: [].one { 99 } #=> 99 ``` ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-87261 * 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/