220 30488 article Path: news.gmane.org!.POSTED!not-for-mail From: Peter Koch Larsen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: enum_cast proposal Date: Wed, 11 Jan 2017 20:23:08 +0100 Lines: 53 Approved: news@gmane.org Message-ID: References: <57258435-5d82-48e7-8ed7-3c38682418fb@isocpp.org> <58750288.5080004@gmail.com> <5875286B.7040604@gmail.com> <58764E08.10000@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 1484162597 25924 195.159.176.226 (11 Jan 2017 19:23:17 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 11 Jan 2017 19:23:17 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDRIBXXKZQERBHUM3LBQKGQE5GBWVTQ@isocpp.org Wed Jan 11 20:23:09 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qt0-f199.google.com ([209.85.216.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cROUE-0005rN-BQ for gclcip-std-proposals@m.gmane.org; Wed, 11 Jan 2017 20:23:06 +0100 Original-Received: by mail-qt0-f199.google.com with SMTP id a29sf129499790qtb.6 for ; Wed, 11 Jan 2017 11:23:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject: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=3aepIYIVbb96PVz0rLx+Fo3VP7dbn+HGAyq8lrRFJDw=; b=TeJD9e7JTZI0BWyWZkcanBtYcUB17HaOEkLHhO8Rfjih2aDbGR5KqC8blShd+pRMDu J5eND33+ztLyAwAU/B0NbRQM0X8gzhQJl8R2exdgq+9V9jSp9dz4Y8cPMSwMTHhGJIwZ qngzuhtx7h7o7WDZH1azaL5Gx/PGW+9KA7k4fsVgahaBrksjth632LUuFUv6QHc+GErT Eiw1jCJeaxtX1PByg+wAzAHN8WwzRbti8oIcOjXZR+7L+zE0rI1LV890g8auu8NcXRSy 4PW611bEteXhCS5jc7LTtaTItd7jn1grCAXmpjd6lrvDItlJ1ltyt36BfoKYK4lzmd1X jS+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject: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=3aepIYIVbb96PVz0rLx+Fo3VP7dbn+HGAyq8lrRFJDw=; b=RwFVENuza4Jn4bjvPHzdFOUDiUl8rths3XQ/i3RyPykDlJQqpnnlym0XWBk/Q77i66 gSAIOjVuTrs7Fdz6CjBXt7C78w3d+ELFQS84pXgrKhAxb4Z7f8MUDfE+TRqZnmBzfGan I5mVoiU+to9YC2mAEebBdnwV3eUXuLKVKTOd8BJ7cejJlL1wKW+lShLIOofCGTiBXfVa R6dYSKHU+GsCVZ65ikDpXgJdGYCW7faPYKGjTb5tse/orrkqlXEM4c1pJLr64Ta+eO+c ygBuVfcFLq+81i4eostvpRFsIuvJQn4C0oUeeMi/9Fs67FI6aRkCCLCjkzOfBW68oHfs quUA== X-Gm-Message-State: AIkVDXIRBdqwDzjrInEjt7EwRRnCZnWybjkWIQcLICIYMkSTQURN3IJLHkfRC2iTSpMkKg== X-Received: by 10.200.41.168 with SMTP id 37mr3011277qts.6.1484162590736; Wed, 11 Jan 2017 11:23:10 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.17.154 with SMTP id v26ls4858265otf.0.gmail; Wed, 11 Jan 2017 11:23:09 -0800 (PST) X-Received: by 10.31.53.134 with SMTP id c128mr3973316vka.13.1484162589924; Wed, 11 Jan 2017 11:23:09 -0800 (PST) Original-Received: from mail-vk0-x22c.google.com (mail-vk0-x22c.google.com. [2607:f8b0:400c:c05::22c]) by mx.google.com with ESMTPS id h20si1815525vke.193.2017.01.11.11.23.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 11 Jan 2017 11:23:09 -0800 (PST) Received-SPF: pass (google.com: domain of peter.koch.larsen@gmail.com designates 2607:f8b0:400c:c05::22c as permitted sender) client-ip=2607:f8b0:400c:c05::22c; Original-Received: by mail-vk0-x22c.google.com with SMTP id 137so386739023vkl.0 for ; Wed, 11 Jan 2017 11:23:09 -0800 (PST) X-Received: by 10.31.73.66 with SMTP id w63mr4991096vka.106.1484162589419; Wed, 11 Jan 2017 11:23:09 -0800 (PST) Original-Received: by 10.103.11.5 with HTTP; Wed, 11 Jan 2017 11:23:08 -0800 (PST) In-Reply-To: <58764E08.10000@gmail.com> X-Original-Sender: peter.koch.larsen@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of peter.koch.larsen@gmail.com designates 2607:f8b0:400c:c05::22c as permitted sender) smtp.mailfrom=peter.koch.larsen@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:30488 Archived-At: On Wed, Jan 11, 2017 at 4:23 PM, Matthew Woehlke wrote: > 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. > And? > If that isn't what you want, don't give your enum multiple identifiers > with the same value in the first place. I don't. ;-) > > > So just *don't do that*. But don't artificially nerf your proposed > feature for people that *do* find that useful. Well, I have not proposed anything here - perhaps you should reread this thread? I simply gave an outline as to how I implemented a feature that was close to what is proposed, and tried to bring to attention some of the open questions I experienced while doing that. Personally, I would prefer to not standardize enum_cast. My preference would be to wait for reflection to be implemented. At that point it will probably just be a simple library function. /Peter -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CANPtkny2KM_jOaBb_wB1t0SBh2Sew%2BT2Ht%2BrUv95eXP562JY1A%40mail.gmail.com. .