220 30480 <58764E08.10000@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: enum_cast proposal Date: Wed, 11 Jan 2017 10:23:52 -0500 Lines: 49 Approved: news@gmane.org Message-ID: <58764E08.10000@gmail.com> References: <57258435-5d82-48e7-8ed7-3c38682418fb@isocpp.org> <58750288.5080004@gmail.com> <5875286B.7040604@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: blaine.gmane.org 1484148247 27031 195.159.176.226 (11 Jan 2017 15:24:07 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 11 Jan 2017 15:24:07 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBBCU43HBQKGQEMQN4NGY@isocpp.org Wed Jan 11 16:23:57 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f198.google.com ([209.85.161.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cRKkh-0005hH-6J for gclcip-std-proposals@m.gmane.org; Wed, 11 Jan 2017 16:23:51 +0100 Original-Received: by mail-yw0-f198.google.com with SMTP id v73sf82394938ywg.2 for ; Wed, 11 Jan 2017 07:23:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:x-original-sender:x-original-authentication-results :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=okffxE30YkdyHe7OS4f93G0yo6NGxPb9GOfdfgddlBc=; b=Ot4UdfMp/PuqV46K+njLVplUsG9Os0QibQONhRlTd9xJ5BH5TZ9GfGDIuKp3sKO0nz JtKXQengbnceDPwxm18U8iguJ5wCPmMFmB9yeA5DOCt5IK9w0fNvnlk9TDlGTImTtQZL naPRGFtxMiwqBSEuOj9ajkW7jgcHjuJCX5VKUQ6HNoXA5R33jYtPR6lTijTsIIVHni6q hcASUmnraaQWsM38EQhyoWwjDjYZd96+LCGZnrDRrJ+sxCGSM9d5RyOpEbIirv6HSF76 nfqRmGcjnE7qtuvrPD0Mptf0eUc20gY2BpCC4MnWLqAkmZhnIcq15REc47//P4JMJLlC imQQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=okffxE30YkdyHe7OS4f93G0yo6NGxPb9GOfdfgddlBc=; b=pBfdqfNQClKavhEHjiZjhubtvLOpz8nfngVtzNAotXMXCY9oW42ZXlaRyUmbN0ZJMZ DMK/x72LMz6qoH7DbSR15nAFHSFBRlJIw79hmfWgdzmRpJQRZeYwc9jVbwx+xo/yUxet ejPlS/10GZO4ntQCaKZasVrfmtLmCFWcR5qLzi/qFXPQofzCiqjAtzJkIUb5pU7SbRoI Wqb0zaXPFHdN+UVDNBJZKkvdxN6lxdJOPyOqQmW/So7k0y0E2o3vo/vNBfKQaqX0tOUl ApLCSeX/TKAM6wxVyqYnDqCbw3kNKpdwSY9VDEAa9HGbzq97p455GmTwX3v/4taBI9mA sClg== X-Gm-Message-State: AIkVDXIwdljNzyZbJUafC2KWsC2UioEeYHW7nsR++JQpjhQmW4zHk/KzEaLIarUinjHavw== X-Received: by 10.129.157.68 with SMTP id u65mr2727191ywg.11.1484148235506; Wed, 11 Jan 2017 07:23:55 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.34.211 with SMTP id i202ls1240054ioi.4.gmail; Wed, 11 Jan 2017 07:23:54 -0800 (PST) X-Received: by 10.36.20.66 with SMTP id 63mr8471145itg.103.1484148234463; Wed, 11 Jan 2017 07:23:54 -0800 (PST) Original-Received: from mail-it0-x242.google.com (mail-it0-x242.google.com. 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[66.194.253.20]) by smtp.googlemail.com with ESMTPSA id c9sm3214893ioc.2.2017.01.11.07.23.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 11 Jan 2017 07:23:53 -0800 (PST) In-Reply-To: X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of mwoehlke.floss@gmail.com designates 2607:f8b0:4001:c0b::242 as permitted sender) smtp.mailfrom=mwoehlke.floss@gmail.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:30480 Archived-At: On 2017-01-11 02:58, Peter Koch Larsen wrote: > On Tue, Jan 10, 2017 at 7:31 PM, Matthew Woehlke wrote: >> On 2017-01-10 12:01, Peter Koch Larsen wrote: >>> What do you do if you have an enum with some same_valued elements >>> (enum E { ea = 0, eb = 0})? My implementation forbids this. >> >> Why? >> >> E x = ea; >> assert(x == eb); // will succeed >> >> Such a prohibition makes some sense when converting an enum to a string >> (or to its ordinal), but there is no problem when converting an int to >> an enum (or a string to an enum, for that matter). > > This is exactly my problem. I partially use my library in to do this > stuff, and it could be confusing for the user if you serialize as ea > and get eb back. ....but you will *also* get `ea` back. The values `ea` and `eb` are not distinguishable when represented as either the enum nor as an integer (via value cast). They are only distinguishable as strings or ordinals. If that isn't what you want, don't give your enum multiple identifiers with the same value in the first place. > I also have a bitset class (enum_bitset), where > I as a template parameter define if i set the bit depending on the > underlying enums ordinal values or by its underlying integral value. > In neither case do I see any use of having two enums with the same > value. > Also, I do not see a reason in have two enums with the same value. So just *don't do that*. But don't artificially nerf your proposed feature for people that *do* find that useful. In your above example, the integer 0 is a member of the set of valid values of `E`. The cast should succeed. Remember, you aren't changing the value representation, you're just changing the *type*. -- Matthew -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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