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=-2.6 required=3.0 tests=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 EBDCA1F463 for ; Mon, 23 Dec 2019 22:12:28 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 199F2120AEF; Tue, 24 Dec 2019 07:12:07 +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 034D7120AEE for ; Tue, 24 Dec 2019 07:12:04 +0900 (JST) Received: by filterdrecv-p3las1-5bf99c48d-92c98 with SMTP id filterdrecv-p3las1-5bf99c48d-92c98-20-5E013BB8-71 2019-12-23 22:12:08.71256075 +0000 UTC m=+595584.683840736 Received: from herokuapp.com (unknown [18.233.7.172]) by ismtpd0050p1mdw1.sendgrid.net (SG) with ESMTP id 2Aqn7WxlQQOPLdW9kkuNRA for ; Mon, 23 Dec 2019 22:12:08.667 +0000 (UTC) Date: Mon, 23 Dec 2019 22:12:08 +0000 (UTC) From: wishdev@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 72102 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 16446 X-Redmine-Issue-Author: sawa X-Redmine-Sender: wishdev 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?Z4Ej7Bg37lK69JtZPFJ+UW67gqYKj9Iu8E0xhUBC8OWdd71zGyJZywyRf+Mjk1?= =?us-ascii?Q?dWCj3QgJszXhzs6yi=2F0zuJr0q=2FjhLB63zHFwgf8?= =?us-ascii?Q?8LTRBG6twwDx3WiRLNbh4TLdAXUidSyTRHFDdtA?= =?us-ascii?Q?CEz21O1CWpJFX3W5B6Cf=2Fv4+Sc0LQxs=2FqtGNd09?= =?us-ascii?Q?92VGkz+2kpm700kcM9XQkKKzGoUdP+uDch8=2F0yX?= =?us-ascii?Q?=2FNG01uElJb9VYwII0=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 96443 Subject: [ruby-core:96443] [Ruby master Feature#16446] Enumerable#take_*, Enumerable#drop_* counterparts with positive conditions 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 #16446 has been updated by wishdev (John Higgins). sawa (Tsuyoshi Sawada) wrote: > wishdev (John Higgins) wrote: > >I prefer simpler examples > > ary = [-1, 0, 1] > > My intention of including two `0`s in the example was to show that there remains an asymmmetry; the search is done from the left, not from the right. In principle, we can still extend the paradigm, but I am not asking for that. Nothing wrong with that at all - but I think adding a :reverse options to the methods would accomplish a right to left search feature. As I said - declaring what you want to do as opposed to trying to come up with some group of 2 words descriptions seems the wiser path. Especially looking at concepts like reversing the search direction......... ---------------------------------------- Feature #16446: Enumerable#take_*, Enumerable#drop_* counterparts with positive conditions https://bugs.ruby-lang.org/issues/16446#change-83367 * Author: sawa (Tsuyoshi Sawada) * Status: Open * Priority: Normal * Assignee: * Target version: ---------------------------------------- #16441 led me to think about the issue more generally. When we want to split a series of iterations by the first element that satisfies (or dissatisfies) a condition, we have three factors to consider. (1) Whether we want the condition to work **negatively** or **positively** (2) Whether we want the first element to satisfy (or dissatisfy) the condition to be included in the **left** side or the **right** side of the split (3) Whether we want the **left** side or the **right** side in the returned output This leads us to eight possible combinations to consider. ```ruby enum = [1, 1, 0, 3, 3, 0, 5, 5].to_enum ``` | |(1)|(2)|(3)|method|example| |--|--|--|--|--|--| |1|negatively|left|left|`take_while`|`enum.foo1(&:nonzero?) # => [1, 1]`| |2|negatively|left|right|`drop_while`|`enum.foo2(&:nonzero?) # => [0, 3, 3, 0, 5, 5]`| |3|negatively|right|left||`enum.foo3(&:nonzero?) # => [1, 1, 0]`| |4|negatively|right|right||`enum.foo4(&:nonzero?) # => [3, 3, 0, 5, 5]`| |5|positively|left|left||`enum.foo5(&:zero?) # => [1, 1]`| |6|positively|left|right||`enum.foo6(&:zero?) # => [0, 3, 3, 0, 5, 5]`| |7|positively|right|left||`enum.foo7(&:zero?) # => [1, 1, 0]`| |8|positively|right|right||`enum.foo8(&:zero?) # => [3, 3, 0, 5, 5]`| Proposal #16441 asks for a method that corresponds to case 3 in the table above, but I think that would make the paradigm messy unless case 4 is also implemented. Either cases 3 and 4 should both be implemented, or both not. Actually, the current proposal is not about cases 3 and 4. I would leave that to #16641. In many use cases (including the first example in #16641), we want to detect the "marker element" by which we split the iterations. In the cases above, that can be the element `0`. In such use cases, it is more natural to describe the condition in positive terms (i.e., `zero?`) rather than negative terms (i.e., `nonzero?`). (And in other use cases, it might be the other way around.) So I would like to propose methods that correspond to cases 5, 6, 7, 8 above. Naming of the methods should be done systematically. As a candidate, I came up with the following: ||method| |--|--| |5|`take_before`| |6|`drop_before`| |7|`take_upto`| |8|`drop_upto`| -- https://bugs.ruby-lang.org/