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 B123117C21E4 for ; Sun, 30 Oct 2011 09:07:29 +0900 (JST) Received: from funfun.nagaokaut.ac.jp (funfun.nagaokaut.ac.jp [133.44.2.201]) by kankan.nagaokaut.ac.jp (Postfix) with ESMTP id 64D92EA6710 for ; Sun, 30 Oct 2011 08:57:45 +0900 (JST) Received: from localhost (localhost.nagaokaut.ac.jp [127.0.0.1]) by funfun.nagaokaut.ac.jp (Postfix) with ESMTP id 9B7AD8FC26 for ; Sun, 30 Oct 2011 08:57:45 +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 illNyCh6fzfn for ; Sun, 30 Oct 2011 08:57:45 +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 7A1698FC22 for ; Sun, 30 Oct 2011 08:57:45 +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 387AF952408 for ; Sun, 30 Oct 2011 08:57:44 +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 ABC1C3C21F11A; Sun, 30 Oct 2011 08:57:38 +0900 (JST) Received: from fluorine.ruby-lang.org (www.rubyist.net [210.251.121.216]) by carbon.ruby-lang.org (Postfix) with ESMTP id A69D33C21F103 for ; Sun, 30 Oct 2011 08:57:32 +0900 (JST) Received: from ruby-lang.org (localhost [127.0.0.1]) by fluorine.ruby-lang.org (Postfix) with ESMTP id 80BA23ED2F for ; Sun, 30 Oct 2011 08:57:32 +0900 (JST) Delivered-To: ruby-core@ruby-lang.org Date: Sun, 30 Oct 2011 08:57:32 +0900 Posted: Sun, 30 Oct 2011 08:57:31 +0900 From: Charles Nutter Reply-To: ruby-core@ruby-lang.org Subject: [ruby-core:40519] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact? To: ruby-core@ruby-lang.org Message-Id: References: X-ML-Name: ruby-core X-Mail-Count: 40519 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: mrkn X-Redmine-Issue-Assignee: matz X-Redmine-Issue-Id: 5321 X-Redmine-Mailinglistintegration-Message-Ids: 10007 X-Redmine-Project: ruby-trunk Auto-Submitted: auto-generated X-Redmine-Site: Ruby Issue Tracking System X-Redmine-Host: redmine.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 #5321 has been updated by Charles Nutter. Why is BigDecimal considered inexact? Unlike a float, a value in a BigDrcimal is always represented exactly. The value itself may be and estimate for various reasons (irrational, repeating, ...), but that is a property of the value, not a property of BigDecimal. Or put another way, BigDecimal is not inexact since if it is possible to exactly represent the number in base 10, BigDecimal can represent it exactly. Perhaps the idea of inexact is too fuzzy here...even Float can be exact if the value can be exactly represented in base 2 decimal form with Float's precision. It seems to me that the interesting characteristic of these classes is not whether the value they represent is exact, but whether arithmetic operations using them can be done exactly. By that definition, only Float is clearly inexact; even if the two operands of a floating-point arithmetic operation are exact, the result may not be. The other types do not have this property. ---------------------------------------- Feature #5321: Introducing Numeric#exact? and Numeric#inexact? http://redmine.ruby-lang.org/issues/5321 Author: Kenta Murata Status: Open Priority: Normal Assignee: Yukihiro Matsumoto Category: Target version: Ruby has several numeric classes such as Integer. These classes are classified whether their instances represent numbers exactly. According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error. The exactness of a Complex depends on its real and imaginary parts. Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances. So, if we want to examine whether a number is exactly zero, we must investigate the class of the number. I want simple way to examine the number exactness. I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience. -- http://redmine.ruby-lang.org