220 30174 <1daf67ad-8ee7-4ad6-937b-027ba6020c14@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: enum_cast proposal Date: Tue, 3 Jan 2017 07:21:36 -0800 (PST) Lines: 77 Approved: news@gmane.org Message-ID: <1daf67ad-8ee7-4ad6-937b-027ba6020c14@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1545_1639964131.1483456896854" X-Trace: blaine.gmane.org 1483456908 5240 195.159.176.226 (3 Jan 2017 15:21:48 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 3 Jan 2017 15:21:48 +0000 (UTC) Cc: m.cencora@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBAMDV7BQKGQEG3OCIOY@isocpp.org Tue Jan 03 16:21:44 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f70.google.com ([74.125.83.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cOQu6-0008Cy-Bz for gclcip-std-proposals@m.gmane.org; Tue, 03 Jan 2017 16:21:34 +0100 Original-Received: by mail-pg0-f70.google.com with SMTP id a190sf1238952696pgc.0 for ; Tue, 03 Jan 2017 07:21:38 -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=K8zBtOXS/8xRLEjhunPxd+iyN20HmnU1aysixHMz7Pg=; b=z8cpQsd+CUmuTtLF+PgO4Eurf5vuKUUlSm6SPjFx7JRCYqaQvvMP7y3SfUloe82dgP diSckNbU1NwAz/EuZRnk9rK8bW6lU/hWEnPeJOMfXqLcpE6iIs4ld8sf/9/whGcgWPvL oE0QrqbYaUOLIOJQPGlDtHhQ7GVDJdGkJzSSkP7RGHbpjh67rOlSJBnGCOJaR+NryDho x5s1QdeuuLTxgaDgJHo9NhTovUqd9chnWzcRFaksmgCvEBIVoGLDUXha2AMr20DRyouG JuCfJT6PDxaAwpDVWfThtvhgPqqqcvSJRxxibpH3XFR05RFJEPMkofkHQqaDcVQTar+y 1Zaw== 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=K8zBtOXS/8xRLEjhunPxd+iyN20HmnU1aysixHMz7Pg=; b=B9b5KOeBsLqmDh6Y739OOM8I3m27nplVjUmEmNd68pFzqauDp0+U2gs2TgvntTTaOH Qx7coSULoCgrGkwstG2xHu3i7yfZUj8W7GrLSsdtKpNHraBdh1NCvlcyk/tBowzS9/g2 E2DBi4OWxlEAtVIUcm529NVgF52dJvkOhhfJn2ejz0TxSUS/ZMBqpyEcuNJQ62bNvarR xB1vlBCUfsup8E+uChgCok/JszaZp1iyjM0WhcHsYF7YEK/r0gIXPNlRUmyjdfLC7wWa lGmO2KAemQc0pfTO0ELAilHP5b0G/yH66ZGEhPaUZE5kXFvgAwvp/38RGA1vke0x0fU4 4+CQ== 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=K8zBtOXS/8xRLEjhunPxd+iyN20HmnU1aysixHMz7Pg=; b=HfPJ5zwBehO7/8Q4YwiZaDXektTppHxAzwr/jdFgermR64dy6gm42V79ueTCaPU0q2 79HmzeTRDhfDnaT+voCaVND79UqSlcK1yXzh7GAsv3L4tAm366APV+gLGYgPY+4ncbLO 4HSYcpZSwxvJggtGIdaIdw6l1KcSsjheEuGC1hBTqIdfKMleNDbXXNkwTpSlfepgy8ni vJBaSy8gYDnRSoOGlEpz1qSIx99kLCTMTan+zE8tDfD1sV4a1AmfoANstiTkWsYFA62o 2iqLq0bx+ym9Ky5mdTQZpJp6dkPQAKl7xoM0TyEnhyxUYJaHbEMhYiEMw4OsVsmUZkGu SsOg== X-Gm-Message-State: AIkVDXLX367r3b/rB/ytXhB2fQ71Cebtu787lCaSAXc2NXp3/wQ1IH057WxhEN9mwS6rmw== X-Received: by 10.99.234.5 with SMTP id c5mr36793210pgi.150.1483456898122; Tue, 03 Jan 2017 07:21:38 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.32.170 with SMTP id x39ls40704937ota.23.gmail; Tue, 03 Jan 2017 07:21:37 -0800 (PST) X-Received: by 10.157.20.197 with SMTP id r5mr2851149otr.9.1483456897422; Tue, 03 Jan 2017 07:21:37 -0800 (PST) In-Reply-To: X-Original-Sender: jmckesson@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:30174 Archived-At: ------=_Part_1545_1639964131.1483456896854 Content-Type: multipart/alternative; boundary="----=_Part_1546_1710949020.1483456896854" ------=_Part_1546_1710949020.1483456896854 Content-Type: text/plain; charset=UTF-8 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 enumerator. > 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_cast<>().value()`. Which will incur needless copying if the 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 useless as exceptions get as far as tracking down the problem. A far more descriptive exception would be `bad_enum_cast`. I would say that you should provide both APIs: `enum_cast` for conversion or throwing. And `optional_enum_cast` or somesuch for conversion into an `optional`. -- 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/1daf67ad-8ee7-4ad6-937b-027ba6020c14%40isocpp.org. ------=_Part_1546_1710949020.1483456896854 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Tuesday, January 3, 2017 at 4:56:05 AM UTC-5, m.ce...@g= mail.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 enume= rator.

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_cast= <>().value()`. Which will incur needless copying if the conversion wo= rked. And if it doesn't work, an exception will be thrown.

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

I would say that you should pro= vide both APIs: `enum_cast` for conversion or throwing. And `optional_enum_= cast` or somesuch for conversion into an `optional<enum>`.

--
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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/1daf67ad-8ee7-4ad6-937b-027ba6020c14= %40isocpp.org.
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