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=-3.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS shortcircuit=no autolearn=ham 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 5A4E51F461 for ; Fri, 6 Sep 2019 13:18:59 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 86E0C120A5D; Fri, 6 Sep 2019 22:18:51 +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 482CB120976 for ; Fri, 6 Sep 2019 22:18:49 +0900 (JST) Received: by filter0171p3mdw1.sendgrid.net with SMTP id filter0171p3mdw1-16926-5D725CBA-11 2019-09-06 13:18:50.304856413 +0000 UTC m=+246167.005745076 Received: from herokuapp.com (unknown [100.24.30.249]) by ismtpd0029p1iad2.sendgrid.net (SG) with ESMTP id rXi9vYKWT5CymybEGHdjZQ for ; Fri, 06 Sep 2019 13:18:50.241 +0000 (UTC) Date: Fri, 06 Sep 2019 13:18:50 +0000 (UTC) From: daniel@dan42.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 70354 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 16147 X-Redmine-Issue-Author: sammomichael X-Redmine-Sender: Dan0042 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?8sy4RigFvRTdBfCVJrT9zb2J88PC92TMQwdNgaWYaq4IbqD+Rc040O8wrXLbCg?= =?us-ascii?Q?iNxKQWLuRPhxHiX3H46B9TVPuDJG8R8sIgdceZd?= =?us-ascii?Q?MFvxqWCmmPSBZpjNoMJW3CLSD6r6AHRINdINVgz?= =?us-ascii?Q?vTTSBJ52ofXp0ZelTTB6rEYq3gq1c9OgXixCQOA?= =?us-ascii?Q?zVFm1nxTBcFGAM6DnczYOoAW2sjjLuQUMGg=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 94799 Subject: [ruby-core:94799] [Ruby master Bug#16147] List Comprehensions in Ruby 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 #16147 has been updated by Dan0042 (Daniel DeLorme). What's wrong with existing well-established ruby idioms? ```ruby (1..0).to_a (1..0).select(&:even?) (1..0).select(&:even?).map{ |x| x**2 } (1..0).map{ |x| x**2 } ``` or in ruby 2.7: ```ruby (1..0).to_a (1..0).select(&:even?) (1..0).select(&:even?).map{ _0**2 } (1..0).map{ _0**2 } ``` or if #16120 was accepted ;-D ```ruby (1..0).to_a (1..0).select{.even?} (1..0).select{.even?}.map{.**2} (1..0).map{.**2} ``` ---------------------------------------- Bug #16147: List Comprehensions in Ruby https://bugs.ruby-lang.org/issues/16147#change-81420 * Author: sammomichael (Samuel Michael) * Status: Open * Priority: Normal * Assignee: * Target version: * ruby -v: * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN ---------------------------------------- ## List comprehensions are present in many languages and programmers are quite fond of their simplicity and power. Add to that the fact that Ruby has a for...in loop that is rarely used but could possibly be repurposed. ### Currently we can already do a hack like this to make Ruby support list comprehension syntax: ``` ruby S = [for x in 0...9 do $* << x*2 if x.even? end, $*][1] # [0, 4, 8, 12, 16] ``` Still, it would be far nicer if the for...in loop would return the desired array automatically, this is one way to approach that taking advantage of lambda bracket invocation syntax: ``` ruby c = -> x do $*.clear if x['if'] && x[0] != 'f' . y = x[0...x.index('for')] x = x[x.index('for')..-1] (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << #{y}") x.insert(x.length, "end; $*") eval(x) $*) elsif x['if'] && x[0] == 'f' (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << x") x.insert(x.length, "end; $*") eval(x) $*) elsif !x['if'] && x[0] != 'f' y = x[0...x.index('for')] x = x[x.index('for')..-1] (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << #{y}") x.insert(x.length, "end; $*") eval(x) $*) else eval(x.split[3]).to_a end end ``` so basically we are converting a string to proper ruby syntax for loop then we can use python syntax in a string to do: ``` ruby c['for x in 1..10'] c['for x in 1..10 if x.even?'] c['x**2 for x in 1..10 if x.even?'] c['x**2 for x in 1..10'] # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] # [2, 4, 6, 8, 10] # [4, 16, 36, 64, 100] # [1, 4, 9, 16, 25, 36, 49, 64, 81, 100] ``` -- https://bugs.ruby-lang.org/