220 33228 article Path: news.gmane.org!.POSTED!not-for-mail From: John McFarlane Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: safe integrals comparison Date: Sun, 16 Jul 2017 21:57:58 -0700 (PDT) Lines: 153 Approved: news@gmane.org Message-ID: References: <66f9bab2-7220-4bf1-afb7-77c5efa1bac3@isocpp.org> <4a572c09-5142-4834-a907-93c3cc87e79c@isocpp.org> <0537f2f2-645d-4a75-826b-c7f8fba9291e@isocpp.org> <0b338a7a-6d2c-44cb-ac96-6ca8bb8b992c@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_977_1046310725.1500267478166" X-Trace: blaine.gmane.org 1500267484 25445 195.159.176.226 (17 Jul 2017 04:58:04 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 17 Jul 2017 04:58:04 +0000 (UTC) Cc: federico.kircheis@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDS7B7WQUYOBBVUHWHFQKGQEN5TJPJQ@isocpp.org Mon Jul 17 06:58:00 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 1dWy6V-0006BN-0x for gclcip-std-proposals@m.gmane.org; Mon, 17 Jul 2017 06:57:55 +0200 Original-Received: by mail-qt0-f199.google.com with SMTP id n42sf68702448qtn.10 for ; Sun, 16 Jul 2017 21:58:00 -0700 (PDT) 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:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=wcx4mp5LtlAVfHtj49AUwNxkj+s8/Lk+ceZMGEg1J9U=; b=aa0Bowp5l20pNwV4XCE1sAoPTDePLf6UUM7XMgmoyuB8ycewGa91ZQY2mDsTJgLjxz a0cdnabmLOMXiElfQtrJoROYbXCeaJ319ZhTGJ40lzBUgE2C+Kj4IdXfb6PnqtPv6v4/ 3LR66Bj/U51LuArtO3l2w3gNeZTczPiMXzonKOopynqZ0gjLXqRdnljxkQIuD7H8e49n l5/rId9rpNwbY45tZlsERAQyhV1ABScXj761W+AfZr4PZklXyNvr2xToEFRFUMpHKq2H KP80tJnLQj3n+W4VbfuyLPd1YJFDSxOhKR3PZI4evKjlD1ERjYjw+RHkgGe4ssYuA+Sl wtMA== 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:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=wcx4mp5LtlAVfHtj49AUwNxkj+s8/Lk+ceZMGEg1J9U=; b=tvEI/fpeWsqI2pp13DLLnSVRCKTzW28cHW9V/Y0HYfoVW/pphb8eoKZTUUC0SMUC8a zW1W7AlenFWu+HFvR9qLL+Rc7XhObxW5tRdRv0dFiZnwPNyoGXyMAb1d5p4Kr6U8vcdg dlo5n2R1oY+GP3U9WR2UsRfPo1Qf2VjVNvZMc1O0bM9etITBwGyDa9QYiX33pluaFTcx mouFqWyIjeXchgQJ5uDdsOpMT11T+sHYohFYNIs2tBGe5GG5/DrWdrP3MsHDluzb79dW teULw7Wy9X1DrqzTexgpxoVzndLUZb2wBLAmS/cpa2TH28MAqlbfE3MW+EEJVdarQu6C NPfQ== 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=wcx4mp5LtlAVfHtj49AUwNxkj+s8/Lk+ceZMGEg1J9U=; b=S0QN+e+T3tC8k9Kbz3sQC6PjaJW7CwXf92m0Nx9rD91ZBoLNBQwpCGhT4eHF2Il52v /CENAxaftavb6OC7kSqdJsMO57ygjCrh542axXX9lS9xE02MoGiMn1EiyNk5ZAcBNKvu LZRjRj+Do6XfiAdCdt56D723nvGhQ3YaQFbwk+wvN+nOuo+HxNem+FFlcVU9Akg4PEzB dWsbUBu1jiYnkF5LRBDwmLY7HnqtSwpqB9ApfDmbIcNe4uUpHqHkTnW79c7Hk3w+3eG0 D+qgiXf4m3tkswgaO4h8MatVCk43gsAIOJXtjV0QX6cL3FEGJpk+un0kUQxEhyUmH4eo TebQ== X-Gm-Message-State: AIVw110eMzMO7r9RI/b73+8gxhrTzK+341VA27cXkoC4SzqliwX7A6+N j7+JrjK7nxAXzc5M X-Received: by 10.200.45.124 with SMTP id o57mr14129152qta.26.1500267480328; Sun, 16 Jul 2017 21:58:00 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.44.69 with SMTP id i66ls2937416iti.9.canary-gmail; Sun, 16 Jul 2017 21:57:58 -0700 (PDT) X-Received: by 10.31.77.2 with SMTP id a2mr74892vkb.5.1500267478771; Sun, 16 Jul 2017 21:57:58 -0700 (PDT) In-Reply-To: <0b338a7a-6d2c-44cb-ac96-6ca8bb8b992c@isocpp.org> X-Original-Sender: mcfarlane.john@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:33228 Archived-At: ------=_Part_977_1046310725.1500267478166 Content-Type: multipart/alternative; boundary="----=_Part_978_395160080.1500267478167" ------=_Part_978_395160080.1500267478167 Content-Type: text/plain; charset="UTF-8" On Sunday, July 16, 2017 at 12:34:15 PM UTC-7, federico...@gmail.com wrote: > > I think the changes were just minor fixups (add references, make some > sentences more clear), but to be honest I didn't give the version number a > thought. I'll probably increase it. > Until publication, it should use D, not P. Here are some guidelines: https://isocpp.org/std/standing-documents/sd-7-mailing-procedures-and-how-to-write-papers > > I'm unaware of P0105, I've only found this discussion: > https://groups.google.com/a/isocpp.org/forum/#!topic/std-discussion/TDSkjdJS1M0 > You can use "http://wg21.link" to look up papers, e.g. wg21.link/P0105 A list of published papers can be found here: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/ > > I do not think that those function should work with floating point types, > since the arithmetic is completely different because of rounding, infinity > values, and nan. > The arithmetic of integral types, if no overflow occurs, is error-free, > and the comparison operators behave well to each other, for example 'a is equivalent to '!(b<=a)' for every a and b, unfortunately for floats this > is not true. > I would therefor prefer not to supply overloaded functions for floating > types, but only for integral types, this way we can eventually add them > afterward. > I also think that situations where you need to compare different float > types are not so common as with integral types. And since all float types > are signed, there are usually no unsafe conversions. > > That all makes sense. At least leaving the door open seems wise. > > I didn't think about user-provided types. > > Since users can't add types that will pass the "std::is_integral" test, > everyone if free to add his own overload in the global or in a separate > namespace without risking to pick the wrong function. > I think you can provide overloads in the std::namespace, but I do not know > exactly on which situations. But I'm unsure if it would be really useful. > > In my mind, there are two situations where you may want to provide your > function > > 1) A custom comparison operator takes the user provided class as a > parameter and a integral. > 2) The class is implicitly convertible to some integral type. > > Maybe it would make sense if you do not want to make the conversion > explicit, I need to think about it. > I'm not sure what the best way is to provide customization points but making user-defined types work with existing APIs seems achievable and of potential benefit. Cheers John -- 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/dba2f844-8b2f-45ed-875f-2a85460056e8%40isocpp.org. ------=_Part_978_395160080.1500267478167 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Sunday, July 16, 2017 at 12:34:15 PM UTC-7, federico...= @gmail.com wrote:
I think the changes were just minor fixups (add references, make some s= entences more clear), but to be honest I didn't give the version number= a thought. I'll probably increase it.

U= ntil publication, it should use D, not P.=C2=A0 Here are some guidelines: h= ttps://isocpp.org/std/standing-documents/sd-7-mailing-procedures-and-how-to= -write-papers

I'm unaware of P0105, I've only found this discussio= n: https://groups.google.com/a/isocpp.org/forum/#!topic/std-= discussion/TDSkjdJS1M0

You can use &quo= t;http://wg21.link" to look up papers, e.g. wg21.link/P0105
A list of published papers can be found her= e: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/

I do not think that = those function should work with floating point types, since the arithmetic = is completely different because of rounding, infinity values, and nan.
T= he arithmetic of integral types, if no overflow occurs, is error-free, and = the comparison operators behave well to each other, for example 'a<b= ' is equivalent to '!(b<=3Da)' for every a and b, unfortunat= ely for floats this is not true.
I would therefor prefer not to supply o= verloaded functions for floating types, but only for integral types, this w= ay we can eventually add them afterward.
I also think that situations wh= ere you need to compare different float types are not so common as with int= egral types. And since all float types are signed, there are usually no uns= afe conversions.

That all makes s= ense.=C2=A0 At least leaving the door open seems wise.

I didn't think about user-pr= ovided types.

Since users can't add types that will pass the &qu= ot;std::is_integral" test, everyone if free to add his own overload in= the global or in a separate namespace without risking to pick the wrong fu= nction.
I think you can provide overloads in the std::namespace, but I d= o not know exactly on which situations. But I'm unsure if it would be r= eally useful.

In my mind, there are two situations where you may wan= t to provide your function

1) A custom comparison operator takes the= user provided class as a parameter and a integral.
2) The class is impl= icitly convertible to some integral type.

Maybe it would make sense = if you do not want to make the conversion explicit, I need to think about i= t.

I'm not sure what the bes= t way is to provide customization points but making user-defined types work= with existing APIs seems achievable and of potential benefit.

Cheer= s
John

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
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/dba2f844-8b2f-45ed-875f-2a85460056e8= %40isocpp.org.
------=_Part_978_395160080.1500267478167-- ------=_Part_977_1046310725.1500267478166-- .