220 30178 article Path: news.gmane.org!.POSTED!not-for-mail From: m.cencora@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: enum_cast proposal Date: Tue, 3 Jan 2017 08:12:29 -0800 (PST) Lines: 104 Approved: news@gmane.org Message-ID: References: <1daf67ad-8ee7-4ad6-937b-027ba6020c14@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1183_727352945.1483459949335" X-Trace: blaine.gmane.org 1483459960 25477 195.159.176.226 (3 Jan 2017 16:12:40 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 3 Jan 2017 16:12:40 +0000 (UTC) Cc: m.cencora@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBD7YFUMJRYMBB4M2V7BQKGQEJTAUIUI@isocpp.org Tue Jan 03 17:12:36 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f199.google.com ([209.85.161.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cORhN-0005Gy-VI for gclcip-std-proposals@m.gmane.org; Tue, 03 Jan 2017 17:12:30 +0100 Original-Received: by mail-yw0-f199.google.com with SMTP id b66sf528262041ywh.2 for ; Tue, 03 Jan 2017 08:12:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=YrGua2Sj5NBcHgrDqA8dI3m5o+7jCTOVLKxuxy7Ciaw=; b=EyFSfTmV1AW+XtwaW0G+sJYjQ+R5zpaPFSlG6nGiGQPd2f05NmFU4YaK9JpegbHBBK tgPpuhm54aITOFAC3WxH4MbHh3ts4nvPAbAtRr4diaTY/jbU4OsmCaivFoqwEK+VxxfP yMzSdpinBw+COlN9gcaacFaO6cRbpx9Ox2+261Ocw5rAytmq3frpKp+CE2bB5kp99rZ5 ND5Dqv/jvvX5DldlVjMByejE/tfdzLsGbS8ka4dqo6hBTEE7i7gxS48O3iDiAez7PFG7 K4KVYEtpCDSNg9A30EEGC+h7NdNYS9nbM5l2c/gpQZCWDV+5rNyGmdkt+3MP8NVOsLe4 eqpA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=YrGua2Sj5NBcHgrDqA8dI3m5o+7jCTOVLKxuxy7Ciaw=; b=lKwX1umrHL8h80GYJ0hKLosT9Pn81h9ruHMC2OlHLYujO82B1fJUeOORsycBqWRqrO ksbo6YL7XHc3mMSt5Ids85M+xxTsPqXnubIhgQTLPwMrvvEKRcDx/llBF3lDox/LzlfB y1CVkK7PycRG3Va+Ni9rMne6j1lvfCDXc5UhlNQAFNMDySHb87es8jkYWffZE7m4Jke9 UcPFfl84jAHKiskp8UnUulwt0XV/yuIWlZHr97XkxDBb1cr9ZVfYW2wUrUn+j/W/bDXi tIRW0psE3wD36+Os6g2FbHXeEhXf6vw9SJkm6Hvz2s5aZV+eurGJr7rvECGWjgFddJu8 SLew== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=YrGua2Sj5NBcHgrDqA8dI3m5o+7jCTOVLKxuxy7Ciaw=; b=f1tA5xmWsBZkZW31REo5npiHrKPESKgcdoPFjbQcvHYL9YsE+21kzEb9WpYD6ZbP7J XlvDmPjYiTuPpoga5MM+HS1PBr7zV7bWqk+3lLBUctwGArpBNu6pTRp0vLcmj1kdGHM+ toihtDi7++Y3h9uj4kqlZ4JpqfR8moe/GsO5YQgqtQtrcVa3JHolncWyLGWGrOEp3JEN i3rT+MhJ82P7O7kkctZOWwktiJLXFD5xEZGYD/9HoT+jK+yVnnUINWempiDLHZi66isl Vdtwf7Zfq+pZvynJ2FDkER6AiQOtvofg/kvhio51MJad9zq5ClNMH90glznWSBHVBU78 rnMA== X-Gm-Message-State: AIkVDXIdGupK8TOEey3ho1/IuwEnZHy2dpwt3r2jWyagG4c/YhWx/idfFedejkgc/WXgbQ== X-Received: by 10.13.240.135 with SMTP id z129mr18295586ywe.121.1483459953905; Tue, 03 Jan 2017 08:12:33 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.31.122 with SMTP id x55ls21834060otx.36.gmail; Tue, 03 Jan 2017 08:12:33 -0800 (PST) X-Received: by 10.157.18.211 with SMTP id g77mr2879291otg.14.1483459953226; Tue, 03 Jan 2017 08:12:33 -0800 (PST) In-Reply-To: <1daf67ad-8ee7-4ad6-937b-027ba6020c14@isocpp.org> X-Original-Sender: m.cencora@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:30178 Archived-At: ------=_Part_1183_727352945.1483459949335 Content-Type: multipart/alternative; boundary="----=_Part_1184_630430329.1483459949335" ------=_Part_1184_630430329.1483459949335 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable W dniu wtorek, 3 stycznia 2017 16:21:37 UTC+1 u=C5=BCytkownik Nicol Bolas= =20 napisa=C5=82: > > On Tuesday, January 3, 2017 at 4:56:05 AM UTC-5, m.ce...@gmail.com wrote: >> >> Hi, >> >> I propose to add a enum_cast function that safely casts int value to a= =20 >> target enum type if int value represents a valid enumerator. >> > > It should not return an `optional`. It should either correctly cast or=20 > *throw*. Why? > > Consider how users will use it. You're going to see a lot of people doing= =20 > `enum_cast<>().value()`. Which will incur needless copying if the=20 > conversion worked. And if it doesn't work, an exception will be thrown. > > What exception will that be? `bad_optional_access`. Which is about as=20 > useless as exceptions get as far as tracking down the problem. A far more= =20 > descriptive exception would be `bad_enum_cast`. > > I would say that you should provide both APIs: `enum_cast` for conversion= =20 > or throwing. And `optional_enum_cast` or somesuch for conversion into an= =20 > `optional`. > At this point I consider chosing a error reporting way bike-shedding. Let's focus on actual functionality it provides for now: check if provided int corresponds to any of the enumerators of given enum. --=20 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 e= mail 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/ea4c8ec9-5f0e-42fb-8928-35bc47e4fd96%40isocpp.or= g. ------=_Part_1184_630430329.1483459949335 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
W dniu wtorek, 3 stycznia 2017 16:21:37 UTC+1 u=C5=BCytkow= nik Nicol Bolas napisa=C5=82:
<= div dir=3D"ltr">On Tuesday, January 3, 2017 at 4:56:05 AM UTC-5, m.ce...= @gmail.com wrote:
Hi,

I propose to add a enum_cast function that safely= casts int value to a target enum type if int value represents a valid enum= erator.

It should not return an `optional`= .. It should either correctly cast or throw. Why?

Consider how= users will use it. You're going to see a lot of people doing `enum_cas= t<>().value()`. Which will incur needless copying if the conversion w= orked. And if it doesn't work, an exception will be thrown.

What= exception will that be? `bad_optional_access`. Which is about as useless a= s exceptions get as far as tracking down the problem. A far more descriptiv= e exception would be `bad_enum_cast`.

I would say that you should pr= ovide both APIs: `enum_cast` for conversion or throwing. And `optional_enum= _cast` or somesuch for conversion into an `optional<enum>`.

At this point I consider chosing a error= reporting way bike-shedding.

Let's focus on a= ctual functionality it provides for now:
check if provided int co= rresponds to any of the enumerators of given enum.

--
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To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/ea4c8ec9-5f0e-42fb-8928-35bc47e4fd96= %40isocpp.org.
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