220 30462 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, 10 Jan 2017 08:20:11 -0800 (PST) Lines: 93 Approved: news@gmane.org Message-ID: References: <57258435-5d82-48e7-8ed7-3c38682418fb@isocpp.org> <58750288.5080004@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_5088_1591528047.1484065211089" X-Trace: blaine.gmane.org 1484065218 2286 195.159.176.226 (10 Jan 2017 16:20:18 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 10 Jan 2017 16:20:18 +0000 (UTC) Cc: m.cencora@gmail.com, gmisocpp@gmail.com, mwoehlke.floss@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBPET2TBQKGQEUSWCZEQ@isocpp.org Tue Jan 10 17:20:10 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-io0-f197.google.com ([209.85.223.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cQz9c-0008E4-OP for gclcip-std-proposals@m.gmane.org; Tue, 10 Jan 2017 17:20:08 +0100 Original-Received: by mail-io0-f197.google.com with SMTP id 101sf112077988iom.7 for ; Tue, 10 Jan 2017 08:20:13 -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=xm2BIUq/ZQY2v0rloRvLkXarItZCr2QPT7w9mlAukTU=; b=qFj0zPPypT2i5kAQRJZ+k3ADLcSGi/FZ1FsYGb3cYmcY4ehRlVurBBUUby9/Xtgb/j n4wYhNgTfEnhfMBpWeyoCc/RuHybcsfCFU6qJUhsz8WBYkg9Ms+3ZiU42ylAH2bZoLIx fvfud4F402qxF7ldzB7MjYLRTyIJtqK+loQ/n7oo2sZfGXztOF3HUbbnbHp0ZDXaQUbe noGm195+UhAPmnmAv27Fhn0IB4/r9/clzXPnIPmMluGbtEAYAcxNrscCZVWxupP0eCa6 W0DNAx3LhOTHXk/6/W+YYdvJQcjcbtPmNzTiAAEcYyzYvF8H5udyEzPg6GsaQYo9qxI/ zVDQ== 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=xm2BIUq/ZQY2v0rloRvLkXarItZCr2QPT7w9mlAukTU=; b=fs2zJxfrIn66LSKaqiF4Nbrd3P3C5KDte6HF1Ul/bcgBk+A/8qREhm+H64l+aYBVZh riyo5GmE9/uadirvQVr98vrxf9Db+GUB2LIbE+MwBS6w0x0gdTMouP+HfLK42EYql2f1 YQEilMYplWgJJbO9fI7Nni6TBHq8ceWho/tvTySjdwd9pLl63fv5AmwUV2bhLYXXMBhu 2U5sVyoQB3ki+mWsmflfcugAEM/YeRJ6Vdhy6qKX5S/yZ8ZssdHuT0Ib48v49Y5c+Ec6 LBAKQh2x3NL/bYDbtwR7KyUIQdDhUXpoFw2IeY4uQMu9SmZDcjXiMFM3sgBxhhXSF/YZ zE3Q== 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=xm2BIUq/ZQY2v0rloRvLkXarItZCr2QPT7w9mlAukTU=; b=QDAGXG6yEgHrMSa0vb0wnFyzi7ZXdfIH1zQD4iMHR2/wrazopoCIJSk9Szooh5Dj02 lxetxaY1+t7uoaGFUecXeXyXOp1cZWq+lc2MZGoheQON79hAAqQ2sXXZD4ztIg8zcQd2 +a6SZkDYDb0PtghvfhXZ58QP99aO/UMR3UFuYbOfJfiu7+ZSIHQNxk4EARo/aFmh6wMb U/Y+pUhl0LkFatVGaW8lrhhF+6UTjHurqlfG7Jlu0jgh4YM16BjlhY7u2+x1N60v3OK2 FPLvyDQLkbkrWHxddWwldTACPe8p+Aiz5e890XKBG/PcBtWFUZIJi46+KIbB3c5iJuA1 bw3w== X-Gm-Message-State: AIkVDXLmQtlTT6I9U2BAIHFy7VIxuTP1lGq/Cn/Mk96dpVcdOhe4Iz0nxbJ3ff+SqPb40Q== X-Received: by 10.36.67.3 with SMTP id s3mr1088093itb.0.1484065213152; Tue, 10 Jan 2017 08:20:13 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.2.1 with SMTP id 1ls134942otb.26.gmail; Tue, 10 Jan 2017 08:20:12 -0800 (PST) X-Received: by 10.157.8.134 with SMTP id 6mr258981otf.17.1484065212490; Tue, 10 Jan 2017 08:20:12 -0800 (PST) In-Reply-To: <58750288.5080004@gmail.com> 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:30462 Archived-At: ------=_Part_5088_1591528047.1484065211089 Content-Type: multipart/alternative; boundary="----=_Part_5089_1816503418.1484065211089" ------=_Part_5089_1816503418.1484065211089 Content-Type: text/plain; charset=UTF-8 On Tuesday, January 10, 2017 at 10:49:34 AM UTC-5, Matthew Woehlke wrote: > > On 2017-01-10 10:31, m.ce...@gmail.com wrote: > > For sure baseline API must be exception-free. > > Do we really want to additionally support API that throws on error? > > I *really* hope we can use something like std::expected; this is a > textbook use case for that, and makes it trivial to have a > throw-on-error API (just grab the value from the expected without > checking it first; this will turn around and throw if the value is not > there). > But the fact that it's throwing the wrong exception makes it useless from an exception handling perspective. If you want an API to throw, you want it to throw a *meaningful* exception type, not the same kind of exception that 20 other APIs throw. So yes, we really do need to support a throwing API. I say we should have 3 interfaces: * `can_enum_cast`: specifies whether the value is in an enumeration. This is where the compiler magic comes in, of course. * `enum_cast`: Converts to the enumeration type, or throws if it cannot. * `enum_cast_opt`: Returns an `optional`. The first allows you to build whatever tools you want. But we have default tools for C++'s standard mechanisms: throwing and `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/e85f0d46-f244-42fe-a276-b4e18b3d627f%40isocpp.org. ------=_Part_5089_1816503418.1484065211089 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Tuesday, January 10, 2017 at 10:49:34 AM UTC-5, Matthew= Woehlke wrote:
On 2017-01-10 1= 0:31, m.ce...@gmail.com wrote:
> For sure baseline API must be exception-free.
> Do we really want to additionally support API that throws on error= ?

I *really* hope we can use something like std::expected; this is a
textbook use case for that, and makes it trivial to have a
throw-on-error API (just grab the value from the expected without
checking it first; this will turn around and throw if the value is not
there).

But the fact that it's throwing th= e wrong exception makes it useless from an exception handling perspective. = If you want an API to throw, you want it to throw a meaningful excep= tion type, not the same kind of exception that 20 other APIs throw.

= So yes, we really do need to support a throwing API. I say we should have 3= interfaces:

* `can_enum_cast`: specifies whether the value is in an= enumeration. This is where the compiler magic comes in, of course.
* `e= num_cast`: Converts to the enumeration type, or throws if it cannot.
* `= enum_cast_opt`: Returns an `optional<Enum>`.

The first allows = you to build whatever tools you want. But we have default tools for C++'= ;s standard mechanisms: throwing and `optional`.

--
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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/e85f0d46-f244-42fe-a276-b4e18b3d627f= %40isocpp.org.
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