220 30247 article Path: news.gmane.org!.POSTED!not-for-mail From: Peter Koch Larsen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: enum_cast proposal Date: Wed, 4 Jan 2017 20:28:38 +0100 Lines: 78 Approved: news@gmane.org Message-ID: References: <64617344.0Ggdhq6B90@tjmaciei-mobl1> <10490049.adee8Rr8fZ@tjmaciei-mobl1> <8747ddc6-c416-44b9-a8a0-b3a00f835c05@isocpp.org> 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 1483558127 16303 195.159.176.226 (4 Jan 2017 19:28:47 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 4 Jan 2017 19:28:47 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDRIBXXKZQERB2UZWXBQKGQEYBAGS3Q@isocpp.org Wed Jan 04 20:28:41 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f199.google.com ([209.85.192.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cOrEm-0003TB-6M for gclcip-std-proposals@m.gmane.org; Wed, 04 Jan 2017 20:28:40 +0100 Original-Received: by mail-pf0-f199.google.com with SMTP id 127sf489202927pfg.5 for ; Wed, 04 Jan 2017 11:28:44 -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=I6f96mUFgp4vkspYJQvAYXghLpCwg8Pt6TWzXjBZn4o=; b=wTU9jtBZF8fYg1HeXYOeUYBRJBCmcnIfE05WuNFiQA/9g+DmsUwa/Kdg2NTtf4JBlt aeqSjBLUFTG0tnXC2RVNgW/PNYXXE5uWz/DxYbRnsNZlPDLpJko3jsCMMjHSIdOwJhuc zV+TT19Haq1ZyjU2fYasG+uGTlBMDsPLIJtjlntFaEUBu7K2tRX/u0qxOnsBfLy2pLBY kTlE3t2610E1K28QSRQO0YNi240ceqwRzkWa8BvB1GOxFGFgD7X7BwQXAKHAm1scvCFA YkMthrJ4FWE9fmHNLTHoVEsCuEGALWoJ18EqxJfCjC5og8VSZAMROEss16Ed7pi0NVAo Rgvg== 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=I6f96mUFgp4vkspYJQvAYXghLpCwg8Pt6TWzXjBZn4o=; b=pZbzsGBDPuVbYKOKwllBBY8yhngiknMSKvczfJZIen9/gPDqKj0agWdUMI0Y+SGFy4 FcT3GudTFr2+UvRtpib2CDVXI257aEAeBKTT8jQd4eohDAlikSp5TfueEfUXWfmydOAa kRXE49ImUON4JvsLYg9CbVMuBi+GSb+jaQUmCXbhRWQJ7Fmt26Wmx0tqIwx1mELv7BV2 R8n2M1jxy3jH6BHqFSohHJ55vKS2rRA5rFvLDLFUC7VJ/IuJkLB5aIs3RASuKjz94Qld 0UqcpLjmYvMCTbXDtaqc6nefgxKzPzW8dxpqK1zhQYFvHnAS1YGV4oEh7fnJehqKXQjg +lWQ== X-Gm-Message-State: AIkVDXJBfzU8oAo77I0+80KcIrEipUCNrZ2hwO2fYNHxZ102Wm4sJBEFS5drXxLNgds7JQ== X-Received: by 10.99.123.73 with SMTP id k9mr32983568pgn.110.1483558123632; Wed, 04 Jan 2017 11:28:43 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.3.145 with SMTP id f17ls2350238otf.27.gmail; Wed, 04 Jan 2017 11:28:42 -0800 (PST) X-Received: by 10.31.88.1 with SMTP id m1mr24837781vkb.83.1483558120176; Wed, 04 Jan 2017 11:28:40 -0800 (PST) Original-Received: from mail-ua0-x244.google.com (mail-ua0-x244.google.com. [2607:f8b0:400c:c08::244]) by mx.google.com with ESMTPS id 44si18259996uau.47.2017.01.04.11.28.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 04 Jan 2017 11:28:40 -0800 (PST) Received-SPF: pass (google.com: domain of peter.koch.larsen@gmail.com designates 2607:f8b0:400c:c08::244 as permitted sender) client-ip=2607:f8b0:400c:c08::244; Original-Received: by mail-ua0-x244.google.com with SMTP id d5so30388315uag.0 for ; Wed, 04 Jan 2017 11:28:40 -0800 (PST) X-Received: by 10.176.74.208 with SMTP id t16mr41650816uae.85.1483558119700; Wed, 04 Jan 2017 11:28:39 -0800 (PST) Original-Received: by 10.103.11.5 with HTTP; Wed, 4 Jan 2017 11:28:38 -0800 (PST) In-Reply-To: <8747ddc6-c416-44b9-a8a0-b3a00f835c05@isocpp.org> 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:c08::244 as permitted sender) smtp.mailfrom=peter.koch.larsen@gmail.com; dmarc=pass (p=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:30247 Archived-At: For what it is worth, I have a small utility library for enumerations (not to elegant, requiring a macro to define the machinery) where you - among other stuff has two functions available that does what you want 1) to_enum(int x): Returns the corresponding enum or an unspecified but valid value. 2) is_enum(int x) Returns true if x represents a valid enum. Thus, If we have the definition enum color { red = 1, green = 200, blue = 3 }; is_enum(100) would return false and to_enum(100) would return either red, green or blue. This approach is in my opinion better than forcing some error-reporting mechanism such as returning an optional or throwing an error. /Peter On Wed, Jan 4, 2017 at 5:33 PM, Nicol Bolas wrote: > > > On Wednesday, January 4, 2017 at 11:16:17 AM UTC-5, Thiago Macieira wrote: >> >> On quarta-feira, 4 de janeiro de 2017 07:20:11 BRST m.ce...@gmail.com >> wrote: >> > Why do you want to use some compiler invented type instead? >> > If enum_cast is a function in standard library, why can't it use another >> > type from same library? >> >> Then it is a function in the standard library. That means it needs to be >> based >> on something else to perform the check, like reflection. > > > There are plenty of functions in the standard library whose implementations > rely on compiler-specific features. You wouldn't be able to implement most > of the type traits without compiler intrinsic or some compiler-specific > knowledge. You can't implement `type_info` or `initializer_list` without the > compiler being involved. And so forth. > > This would simply be one more compiler-based construct. Once we get > compile-time reflection, implementations could become platform-neutral > (though the compiler-equivalent would probably still get faster). > > But how the function gets implemented ultimately has nothing to do with > having it return `std::optional`. > >> >> >> -- >> Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org >> Software Architect - Intel Open Source Technology Center >> > -- > 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/8747ddc6-c416-44b9-a8a0-b3a00f835c05%40isocpp.org. -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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