From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Original-To: poffice@blade.nagaokaut.ac.jp Delivered-To: poffice@blade.nagaokaut.ac.jp Received: from kankan.nagaokaut.ac.jp (kankan.nagaokaut.ac.jp [133.44.2.24]) by blade.nagaokaut.ac.jp (Postfix) with ESMTP id BF03417C5B54 for ; Mon, 2 Apr 2012 10:59:32 +0900 (JST) Received: from funfun.nagaokaut.ac.jp (smtp.nagaokaut.ac.jp [133.44.2.201]) by kankan.nagaokaut.ac.jp (Postfix) with ESMTP id 18B29EA68F9 for ; Mon, 2 Apr 2012 10:42:04 +0900 (JST) Received: from localhost (localhost.nagaokaut.ac.jp [127.0.0.1]) by funfun.nagaokaut.ac.jp (Postfix) with ESMTP id 4EC058FC44 for ; Mon, 2 Apr 2012 10:42:04 +0900 (JST) X-Virus-Scanned: amavisd-new at funfun.nagaokaut.ac.jp Received: from funfun.nagaokaut.ac.jp ([127.0.0.1]) by localhost (funfun.nagaokaut.ac.jp [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id TFZAHo-zxAMi for ; Mon, 2 Apr 2012 10:42:04 +0900 (JST) Received: from voscc.nagaokaut.ac.jp (voscc.nagaokaut.ac.jp [133.44.1.100]) by funfun.nagaokaut.ac.jp (Postfix) with ESMTP id 2D9758FC19 for ; Mon, 2 Apr 2012 10:42:04 +0900 (JST) Received: from carbon.ruby-lang.org (carbon.ruby-lang.org [221.186.184.68]) by voscc.nagaokaut.ac.jp (Postfix) with ESMTP id 526FB952477 for ; Mon, 2 Apr 2012 10:42:02 +0900 (JST) Received: from beryllium.ruby-lang.org (beryllium.ruby-lang.org [127.0.0.1]) by carbon.ruby-lang.org (Postfix) with ESMTP id 1C49F3C21E218; Mon, 2 Apr 2012 10:42:00 +0900 (JST) Received: from fluorine.ruby-lang.org (www.rubyist.net [210.251.121.216]) by carbon.ruby-lang.org (Postfix) with ESMTP id F273D3C21E7D9 for ; Mon, 2 Apr 2012 10:41:53 +0900 (JST) Received: from ruby-lang.org (localhost [127.0.0.1]) by fluorine.ruby-lang.org (Postfix) with ESMTP id DDF7A3ED20 for ; Mon, 2 Apr 2012 10:41:53 +0900 (JST) Delivered-To: ruby-core@ruby-lang.org Date: Mon, 2 Apr 2012 10:41:54 +0900 Posted: Mon, 2 Apr 2012 10:41:53 +0900 From: "shugo (Shugo Maeda)" Reply-To: ruby-core@ruby-lang.org Subject: [ruby-core:44051] [ruby-trunk - Feature #6240] Enumerable#drop with negative argument To: ruby-core@ruby-lang.org Message-Id: References: X-ML-Name: ruby-core X-Mail-Count: 44051 X-MLServer: fml [fml 4.0.3 release (20011202/4.0.3)]; post only (only members can post) X-ML-Info: If you have a question, send e-mail with the body "help" (without quotes) to the address ruby-core-ctl@ruby-lang.org; help= X-Mailer: Redmine X-Spam-Checker-Version: SpamAssassin 3.1.7-deb3 (2006-10-05) on carbon.ruby-lang.org X-Spam-Level: X-Spam-Status: No, score=0.1 required=7.0 tests=BAYES_50,CONTENT_TYPE_PRESENT, FORGED_RCVD_HELO,X_MAILER_PRESENT autolearn=disabled version=3.1.7-deb3 X-Redmine-Issue-Author: marcandre X-Auto-Response-Suppress: OOF X-Redmine-Issue-Id: 6240 X-Redmine-Mailinglistintegration-Message-Ids: 14064 X-Redmine-Project: ruby-trunk Auto-Submitted: auto-generated X-Redmine-Site: Ruby Issue Tracking System X-Redmine-Host: bugs.ruby-lang.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Precedence: bulk List-Id: ruby-core.ruby-lang.org List-Software: fml [fml 4.0.3 release (20011202/4.0.3)] List-Post: List-Owner: List-Help: List-Unsubscribe: Issue #6240 has been updated by shugo (Shugo Maeda). marcandre (Marc-Andre Lafortune) wrote: > > How Enumerable#drop can know the total number of elements? > > The source of elements might be IO. Besides that, the total number of elements might be infinite. > > `drop` would have to consume the whole iteration, indeed, which is why I was talking about a buffer. The buffer holds elements until we know they are not in the last (-n) elements. Here's a Ruby implementation: Ah, I see. It's interesting. Do you have any use case in mind? ---------------------------------------- Feature #6240: Enumerable#drop with negative argument https://bugs.ruby-lang.org/issues/6240#change-25581 Author: marcandre (Marc-Andre Lafortune) Status: Open Priority: Normal Assignee: Category: core Target version: 2.0.0 Currently, Enumerable#drop works only for non-negative arguments. It could be extended so that negative arguments means dropping from the end: [:hello, :world].drop(-1) # => [:hello] This could especially be interesting for `Lazy#drop`, which would keep a circular buffer of elements before yielding them. (1..6).lazy.drop(-3).each{|x| puts x} # -> prints 1, 2 and 3 Thoughts? -- http://bugs.ruby-lang.org/