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=-2.9 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 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 BF7911F464 for ; Sun, 22 Sep 2019 16:47:30 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id A9371120939; Mon, 23 Sep 2019 01:47:22 +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 3DF0E120808 for ; Mon, 23 Sep 2019 01:47:20 +0900 (JST) Received: by filter0031p3iad2.sendgrid.net with SMTP id filter0031p3iad2-27549-5D87A59C-1F 2019-09-22 16:47:24.387386691 +0000 UTC m=+257215.460786735 Received: from herokuapp.com (unknown [54.224.117.74]) by ismtpd0025p1mdw1.sendgrid.net (SG) with ESMTP id sMYOD6tHR7-9Tm0APMgd1w for ; Sun, 22 Sep 2019 16:47:24.217 +0000 (UTC) Date: Sun, 22 Sep 2019 16:47:24 +0000 (UTC) From: eregontp@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 70590 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 16147 X-Redmine-Issue-Author: sammomichael X-Redmine-Sender: Eregon 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?KippOI8ZHtTweq7XfQzW93937kJ4QNWwSBuHnaMEcr3zzUzdebCiUPN5lgKTpk?= =?us-ascii?Q?pHR10B7y5c2bm=2FyvaBqrjc15zNZmGtdtW6LA3Ka?= =?us-ascii?Q?VpnKYtnlOB4XMo7FPCBjeDCl=2F+uzSg5wtpe19ca?= =?us-ascii?Q?wgwbhFLzGROKSr+aNhO21cxhs1RfL676Uoksf7R?= =?us-ascii?Q?Tl3wrzDqALheGE0zWNjIFzYhPaI61=2Fx6tzw=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 95035 Subject: [ruby-core:95035] [Ruby master Feature#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 Eregon (Benoit Daloze). Just my opinion: I don't think we should have list comprehensions in Ruby. They are just a small subset of the far more powerful Enumerable methods, and IMHO are often less readable (e.g., nested list comprehensions in Python are what I would call unreadable). Also, I think they basically don't scale, they might look nice for small expressions, but as soon as it becomes bigger it's no longer possible to use the list comprehension syntax. So I think it's better to use map/select/filter_map directly. ---------------------------------------- Feature #16147: List Comprehensions in Ruby https://bugs.ruby-lang.org/issues/16147#change-81666 * Author: sammomichael (Samuel Michael) * Status: Open * Priority: Normal * Assignee: * Target version: ---------------------------------------- ## 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/